Water bugs (Insecta: Hemiptera: Heteroptera) of Himalayan and sub-Himalayan regions of West Bengal, India

The present study reports a total of 61 Species belonging to 34 genera and 14 families from Darjeeling Himalaya and Jalpaiguri sub Himalaya regions of West Bengal. The study documented 11 new species to science, which were already published, 15 new records to the state and one new record to India. The study showed that the Nepomorphan families are mostly restricted to the slow flowing or to the stagnant ecosystems like ponds or lakes and the running waters are dominated mainly by the Gerromorpha. The key to all family, genera and species of aquatic Hemiptera are provided with their distribution in India and globally. The description of all species with their detail photographs and distribution map were also presented here. The diagnostic characters supported with photographs for each species are also presented here.


INTRODUCTION
The Eastern Himalaya region (EH) is one of the 'Biodiversity Hotspots', and also physiographically diverse encompassing mountains, valleys and floodplains. This region is located at the junction of the Indo-Malayan, Palaearctic, and Sino-Japanese biogeographical realms (CEPF 2005) and is ecologically rich associated with diverse flora and fauna. In fact, the variation in altitude, landscape profiles, climatic condition and geographic complexity of EH region considerably affect formation of varied eco-regions that favour great assemblages of vegetation and unique fauna with a high proportion of endemism and diversity. A recent estimate describes 3,624 species of insects, 50 molluscs, 236 fishes, 64 amphibians, 137 reptiles, 850 birds, and 397 mammalian species from the northeastern states of India (Maheswaran 2012). The largely inaccessible landscape, however, makes biological surveys in this region extremely difficult. As a result, many floral and faunal groups in the unexplored vast forest ranges of this region are taxonomically understudied. Many small invertebrates like insects, in particular, have been neglected or virtually ignored except for the documentation of Lepidoptera (Mani 1986) and of Odonata (Mitra et al. 2010). As this region harbours numerous critical habitats and several protected areas, there is a high possibility to explore many unknown species of insects.
The diversity of aquatic and semi-aquatic Hemiptera comprises all lotic or lentic species that are found in different altitudes. The perennial water bodies ranging from rivers, torrential streams, and tiny steep streams in hilly montane areas, slow-flowing marshy streams, open marshes in valleys, stagnant pools or forested swamps, ponds, lakes, and ditches at lower altitudes, and seasonal ponds during the monsoon are the habitats of these bugs.They, commonly known as 'water bugs', are the integral components of freshwater ecosystems and play an important role in the food web of freshwater ecosystems as predators of other aquatic invertebrates or scavangers (Murdoch et al. 1984). Knowledge of their biology, feeding habits, pre-preadtor relationship is essential to study the fish biology and for proper management of hatcheries (Thirumalai 1999). Besides, they also serve as zoogeographical indicators due to their poor dispersal capabilities (Jordon 1951;Hungerford & Matsuda 1958a b;Thirumalai 1999) and proved as bio-indicators of long-term environmental changes. Knowledge about the diversity and distribution of this group helps in understanding the functional aspects of community structure of aquatic ecosystem and provides the baseline data required for developing strategies for the effective conservation and management of freshwater ecosystems. Some of them are efficient biocontrol agents of mosquito larvae (Saha et al. 2010). However, documentation of these bugs in the current study area is still insufficient. The present study, hence, focuses on the taxonomy, and distribution of aquatic and semi-aquatic Heteroptera in the Himalayan and sub-Himalayan regions of West Bengal.

Study Area
The present study was conducted in two regions of West Bengal-in Darjeeling region, a part of Eastern Himalayan Biodiversity Hotspots, and in Jalapiguri region that encompasses the Himalayan foothills of West Bengal (Fig. 1).
Description: Dorsally, colour varies from pale brown to dark brown. Head yellow with an inverted V-shaped marking towards the anterior margin, a more or less triangular fuscous spot posteriorly. Pronotum overall brown with a more or less rectangular yellow spot medially, lateral margin pale. Head dorsally, with fine punctures, slightly produced ahead of eyes. Head length 1.4mm. Eyes 2.3 times longer than broad. Interocular region three times as wide the eye width. Antenna glabrous, length of antennal segments 1-4: 0.12mm, 0.16mm, 0.22mm, 0.31mm. Pronotum's length 0.73mm, width 2.85mm, with dense punctures, denticulate laterally; posterior margin nearly straight. Hemelytra touching each other at mid-line (Image 3d), each 1.5 times longer than broad, with intense punctures, embolium with sparse, black, short hairs. Propleura rounded posteriorly, with blunt inner propleural projection. Metasternum weakly carinated, metaxipus small, laterally concave with apex more or less acuminate. Abdominal tergites with dense black short hairs, laterally on each side. Tergites II-IV symmetrical, sternum IV-VI with median protrusion, but without peg-like setae. Fore femora with prominent golden setae, mid and hind femora and tibia with dense long golden hairs, claws well-developed and curved.
Male Genitalia: Genital capsule broadly rounded (Image 4f), with scattered golden, prominent hairs. Parandria as in Image 4e, left parandrium much longer and more acuminated towards apex than the right one and right parandrium wide with truncated apex. Aedeagus (Image 4e) elongated and slender, well- sclerotized, its apex slightly acuminated. Left paramere distinctly wider than the right one. Left paramere (Image 4j) stout, gently curved, widened sub-basally and at distal two-thirds of length, slightly constricted near mid-length, tapering towards its narrowly rounded apex, seven spines arranged in two parallel rows. Right paramere (Image 4i) relatively slender, acuminated basally, with nearly uniform width and more concave apically, six stout spines located medially and bunch of setae arising from the concave margin.
Female Genitalia: Subgenital plate (Image 4h) narrowly triangular, with sub-apical and lateral setal tuft and extreme lateral long setal tuft on each side; a broad medial zone, clothed with golden setae.
all Diplonychus having the maximum length and width. Male of D. annulatus carries eggs on their back until they hatch. These predatory bugs feed on other aquatic insects, crustaceans, mosquito larvae (Saha et al. 2010) and even small fishes.

Figure 5. Distribution of D. rusticus
Description: Head length 0.452mm, width 0.71mm. Vertex with rows of obscure punctures throughout the posterior half, head roundly produced infront of eyes. Pronotum black with six yellowish transverse lines. Length of pronotum 0.99mm, width 1.72mm. Eye length 0.91mm and width 0.36mm. Pala of male simple with a curved row of 34 pegs, of which distal 10 pegs slightly more elongated than others. Clavus black with yellow transverse vermiculations which are broken, irregular, and narrower than the spaces. Corium black with fragmented yellow vermiculations. Mid femur with a few long swimming hairs. Fore femur with two pairs of small spines located distally. Strigil moderately large, oblong, consists of seven combs. In males, Figure 8. Distribution of S. promontoria (Distant) in the study area Image 9. a-e. Sigara (Tropocorixa) promontoria (Distant, 1910  2.93 mm. Maximum body width of male is 1.34mm and that of female is 1.31mm. Description: Head pale yellow, with an obscure central elongate orange spot on the anterior part of vertex. A pair of orange clouded spots nears the eyes. Pronotum grayish-brown with its margin yellowish. Base of clavus grayish, corium light brown with three very obscure fragmented dark brown longitudinal stripes continued upto the right membrane. Legs pale yellow with apex of tarsus slightly darkened Venter pale yellow. Head 2.4 times as long as wide (L/W=0.95/0.4). Interocular width 3.4 times wider than eye width (IW/EW=0.41/0.12). Eye length 0.32mm. Length of pronotum 0.33mm and width 0.90mm. Pronotum 2.3 times wider than head. Scutellum as long as wide (0.28mm). Pronotal disc is very finely granulose, anterior margin evenly convex, posterior margin convex but, rather flat centrally. Male fore femur with a single long basal hair on its inner margin, a row of four spines just within the inner margin. Mid femora longer than mid tibiae. Abdominal segments (4th to 8th) 1.04mm in length and 1.16mm in width.
Genitalia: Seventh segment wide and simply lobed on right side. Free lobe of eighth tergite welldeveloped, rectangular. Right paramere arcuate and rather wide, with a slightly button-like apex (Image 13i). Left paramere wide basally, narrows towards the apex (Image 13h).
Global distribution: India, Iran, United Arab Emirates, and Oriental Region.

Micronecta haliploides
Description: A large, elongated oval species. Pale in color with well-marked small black spots on yellowish hemelytra. Head length 0.35mm and width0.53mm. Interocular width 1.9 times as wide as eye width (IW/ EW=0.43/0.23). Eye length 1.5 times longer than width (L/W=0.35/0.23). Pronotum 1.5 times as wide as head width. Width of pronotum 0.79mm. Lateral pronotal margins obsolete.Yellowish hemelytra marked with distinct dark dots. Pronotum transverse and narrow, lateral margins very short. Lateral margins of elytra moderately convexly rounded. Abdominal segments are dark brown or black. Strigil present in male. Two bristles present on sixth sternite.

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Genitalia: Males are with a row of hairs on the right part of eighth segment. This row is absent in the left part of eighth segment bearing the free lobe. Male right and left paramere as in Image 15j & k respectively.

Remarks:
A widespread species. This species is attracted to light and can be caught in light trap.  Description: Light brown elongated species. Head length 0.27mm and width 0.67mm. Interocular width 0.38mm. Head pale yellow with one light reddish longitudinal line on vertex. Eye length 0.41mm and width 0.14mm. Pronotum brownish, length 0.95mm and width 0.36mm. Hemielytra with broken longitudinal stripes that is rarely absent. Lateral margins of hemielytra with four dark patches of which basal patch is the largest and elongated. Males with strigil on the left and the free lobe of eighth tergite on the right side. Length of wings 2.28mm. Male pala is distinct as in Image 16e. Genitalia: Male genital segment is asymmetrical. The free lobe of eighth tergite sigmoid in shape at left part (Image 16j). Male right and left paramere as in Image l & k.

Family Naucoridae Leach, 1815
Oval, flattened bugs with raptorial forelegs. The size varies from 2-15mm, and the colour from brownish to blackish, often marked with yellow or green. The members of this family are easily identifiable by threesegmented simple concealed antenna, absence of ocelli, three-segmented rostrum and with a distinct claw at hind tarsi. The respiratory tube is absent.

Genus Heleocoris Stal, 1876
Diagnosis: Body oval, elongated. Eyes with an external process between outer margin and the anterior angle of the pronotum. Eyes subparallel and anteriorly convergent. Disk of the pronotum regularly and uniformly convex, connexivum posteriorly visible, the corium a little obliquely narrowed from above middle to apex, membrane small. Fore tarsus with two claws. Males have two segments whereas females have only one. Male phallotheca is asymmetrical. Male paramere is greatly reduced. The female subgenital plate is roughly trapezoidal.  Habitat: Small streams and riffles. Remarks: Heleocoris bengalensis was described by Montandon (1910)

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requires further detailed study.

Family Nepidae Latreille, 1802
Body dorso-ventrally flattened or cylindrical (size ranges from 15-55mm) with long and slender legs, the anterior pair being raptorial. These bugs are characterised by single-segmented tarsi and by the absence of ocelli. The long slender, non-retractile respiratory siphon is derived from the 8 th abdominal tergum and has two spiracles at its base.

Subfamily Nepinae Latreille, 1802
Genus Laccotrephes Stal Diagnosis: Body long, dorsoventrally flattened and broad. Generally, brown or grey in colour. Head distinctly narrower than pronotum and partly enclosed in the anterolateral pronotal angles. Compound eyes prominently spherical, black, with rounded margin, eye width less than interocular width. Antennae three segmented, outer margin with numerous setae. Respiratory siphon long, vary in species, may or may not be longer than the body length. Fore leg raptorial with broad femora and sharp claws. Scutellum welldeveloped and wider than long. Fore wings with distinct clavus, corium and membrane, the membrane with distinct venation. Prosternum with a distinct keel.
Description: Smaller in size relative to other species. Head triangular, tapering anteriorly, 1.6 times as long as wide (L/W=1.8/1.1). Eyes oval, small, length 0.63mm. Interocular width 1.95 times wider than eye width (IW/ EW=0.94/0.48). Rostrum 1.36 times in length, stout, thick. Clypeus well-differentiated. Antennae hidden, three-segmented, with stout hairs. Pronotum distinct, almost rectangular. Length of pronotum 2.49mm and width 4.33mm. A transverse suture just above the posterior margin. Scutellum triangular, tapering posteriorly. Prosternum strongly acute along median line. Abdomen flattened, 2.2 times longer than wide (L/W=12.7/5.7). Base of sixth abdominal sternites with small tuft of hairs covering the sub-genital plate proximally. Hemelytra parallel, thick, membrane thin with numerous reticulate veins. Abdomen beneath wings bluish in colour. Fore femora 3.66mm in length and 1.21mm in width in male, with obtusely rounded tooth at base.
Genitalia: Male genital capsule anteriorly shallow, posteriorly broad. Parameres (Image 19f) symmetrical, slightly hooked and articulated in anterior region. Female genitalia triangular and armatured, two pairs of plate like structures forming slender ovipositor.
Remarks: This species is cosmopolitan in distribution. It is a very sluggish species often found under weeds or at the bottom of slow or stagnant water or edges of water bodies. This species possesses sexual dimorphism.

Genus Cercotmetus Amyot & Serville, 1843
Diagnosis: Body elongated, sub-cylindrical with a posterior respiratory siphon, which is usually shorter than the body length. Eyes large, outer margins reflexed downwards. Head with a prominent clypeus. Vertex raised above the eyes. Antenna three segmented, lie in ventral depressions beneath the eyes. Prothorax dorsally divided into two lobes by a transverse groove. Anterior lobe much longer than the posterior lobe. Humeral width always greater than anterior width. Scutellum small, triangular. Clavus and corium coriaceous. Membrane with many small veins. Abdominal tergites flat. Metasternum posteriorly emerginated. First abdominal sternite not visible, third to sixth sternite longitudinally carinate, seventh sternite with operculum. Fore femora irregularly annulated with light and dark brown colour, with one tooth about midway ventrally. Mid femora shorter than hind femora. All tarsi one-segmented.

Remarks:
The Cercotmetus Amyot & Serville is almost similar to Ranatra Fabricius, but can be distinguished by the presence of short and stout respiratory appendages. They are predatory in nature and feed on freshwater shrimps.

Genus Ranatra Fabricius, 1790
Diagnosis: Body elongated, sub-cylindrical, with a pair of posterior respiratory siphons. Head either with a prominent tubercle between eyes or only slightly rose between eyes. Eyes large and globular. Antennae concealed beneath head, not visible from above, three-segmented, second and third segment with numerous spines. Prothorax distally divided into two lobes by a transverse groove. Anterior lobe always longer than the posterior lobe, the posterior margin of posterior lobe always deeply emerginate. Ventrally, prosternum with a median longitudinal keel. Metasternum with a distinct modification or keel. Wing membrane small with many  Morphology: Size: Body length ranges between 19-22mm. Respiratory siphon always shorter than the body, length of respiratory siphon 14-16 mm.
Description: Head length 0.48mm, 1.3 times longer than interocular width (0.35mm). Eye length 0.30mm and width 0.34mm. Vertex rounded between eyes. Pronotum 3.1 times longer than the width (length/ width: 1.4/ 0.45). Posterior lobe of pronotum sparsely punctuate, smaller than the darker anterior lobe of pronotum. Antennal segments with many stout spines, distributed mainly in second and third antennal segments. Respective length of antennal segments 1-3: 0.06mm, 0.02mm, 0.14mm. Metasternum with a prominent median keel (Image 22g), almost flat. Wing length 5.46mm, almost covering the abdomen.  Morphology: Size: Adults may attain a length of about 18.5-23 mm. Respiratory siphon always shorter than body, length ranging between 14-18 mm.
Description: Brownish in colour. Eyes globular, red. Head length 1.45mm and width 0.83mm. Eyes 0.61mm in length and 0.68mm in width. Rostrum

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in Image 23g. Fore femora (Image 23e) broad with a distinct tooth. Hind femora in both sexes reaching upto the posterior margin of sixth sternite. Genital segment: Sixth sternite of female expanded distally distinctly. Operculum almost as long as connexivum. Female ovipositor 1.8mm in length.
Habitat: Fish ponds, lakes with floating vegetation at edges. Montandon (1903) described this species without mentioning the type locality. Lansbury (1972)  Morphology: Size: Male attains a length of 28-31mm, length of respiratory siphon 26.5-29.2 mm. Body length of female ranges from 28.5-33mm and length of respiratory siphon 27-29mm.

Remarks:
Description: Head length 1.30mm, vertex evenly rounded between eyes. Eyes globular, much greater than the interocular region, length of eye 0.98mm and width 1.11mm. Antennae with several stout spines. Anterior lobe much darker and slightly less than twice as long as posterior lobe, length of anterior lobe of pronotum 3.55mm and anterior width 1.68mm. Humeral width 2.43mm. Prothorax anteriorly tricarinate, central keel sharply carinated. Mesosternum rounded and shining, anterior margin emerginated, mesosternum with a 'V' shaped cleft between mid coxae. Metasternum flat, basally triangular, lateral margins concave as in Image  Description: Head length 1.35mm and width infront of eyes 0.89mm, vertex slightly raised between eyes, occasionally developed into a vestigial tubercle. Length of eye 0.65mm and width 0.61mm. Rostrum 0.87mm in length. Interocular width 0.76mm. Second and third segments of antennae mostly black with long, stout spines. Length of anterior lobe of pronotum 3.66mm and width 1.18mm. Length of posterior lobe of pronotum 1.25mm and width 1.77mm. Anterior lobe slightly darker than posterior lobe with an obtuse  Habitat: Ponds, slow-flowing streams, ditches, and puddles.
Remarks: This is one of the smaller species. This is widespread in India and commonly found species.

Family Notonectidae Latreille, 1802
They are truly aquatic forms which differ from all other aquatic bugs (except Pleidae and Helotrephidae) in the habit of swimming on their backs. The notonectids are small, medium-sized (15-20mm), oblong bugs, characterised by four segmented antennae, three to four segmented rostrum, absence of ocelli, nonraptorial legs, and flattened hind legs devoid of claws.

Genus Anisops Spinola, 1840
Diagnosis: Body usually small, slender, but some species are large and attain a length of about 12 mm. Eyes large, may or may not be holoptic. The interocular region with a median longitudinal depression anteriorly. Anterior end of hemelytral commissure with a definite hair-lined pit. The hemelytra not coriaceous. Ventrally,  Rostrum 0.77mm in length, rostral prong shorter than the third rostral segment. Fore femur greatly enlarged at base with pointed apex in male. In female, fore femur broad with numerous setae as in Image 26f.

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Genitalia: The male paramere is little excavate and the female ovipositor with numerous denticles as in Imaeg 26g. The length of ovipositor 0.72mm.
Global distribution: India. Distribution in India: Kerala, Maharashtra, Tamil Nadu, Uttar Pradesh, and West Bengal.
Habitat: Freshwater ecosystems such as rocky streams, rivers, ponds, etc.

Remarks:
The species description is written based on the female as male specimens are not collected.The male descriptions are based on the literature of Brooks (1951) and Thirumalai (1994). Morphology: Size: Body length of male 5.7-6.6 mm, maximum body width of male 1.2-1.6 mm. Body length of female 5.4-6.8 mm, maximum body width of female 1.2-1.7 mm.

Anisops breddini
Description: Body pale in colour dorsally with the elytra pale-greyish. Abdominal sternum dark brown in colour with the keel reddish brown for the greater part and brownish black at the terminal end. Eyes holoptic posteriorly, dorsally lateral margins of eyes slightly convex giving the head an almost conical appearance; head as wide as pronotum. Eye length 0.76mm and width 1.10mm. Lateral margins of pronotum parallel. Hemelytra with reduced membranes. Rostral prong in males slightly longer than the third rostral segment. Fore femora of male strongly swollen. Fore tibia slightly more than one-and-half times as long as tarsus. Stridulatory comb on fore tibia consists of a few irregular teeth in male. Fore femora and tibia 0.87mm and 1.1mm in length, respectively. Mid tibia with a long claw, as long as the third tarsal segment. Abdomen 2.3mm in length and 0.80mm in width.
Genital segments: Male genital segments modified and little elongated. Male paramere as in Imaeg 27h. Female genital segments symmetrical and not modified.
Description: Dorsally stramineous in colour. Eyes brown. Hemelytra hyaline and appear darker due to dark brown body surface. Abdominal venter dark brown or black with keel.In male, the interocular space produced into a prominent cephalic horn with acuminated apex anteriorly as viewed from the above, lateral margins of head rounded. Synthlipsis narrow. Labrum short, apex acuminated, each basal angle bearing a tuft of erected hairs whose tips are curved medianly and form a loop with each other. Head is wider than pronotum. Pronotum with its humeral width more or less twice the median length, posterior margin of pronotum convex, emarginated medially. Rostral prong slightly shorter than the third rostral segment. Stridulatory comb of approximately 18 teeth. Mid tarsal claws strongly curved inward at base.
Genitalia: Male genital segment with tuft of a pair of setae laterally on both sides.Male left and right paramere as in Image 27h & i, respectively. Left paramere broad and right paramere apically curved.
Remarks: This species is a close relative of A. bouvieri Kirkaldy by the shape of the male cephalic horn. It can be differentiated by the presence of marginal row of prominent setae on the inner surface of fore tibia of male.

Genus Nychia Stal, 1860
Diagnosis: Body elongate, oval, whitish dorsally, mostly found in brachypterous forms. Head not as broad as pronotum. Eyes very large, inner margins converging dorsally and meeting each other in posterior third. Antennae three-segmented. Pronotum broader than long with antero-lateral margins distinctly foveate. Claval commissure of hemelytra continuous. Mid femur with a pair of stout bristles ventrally in basal half. Fore and mid tarsi two segmented in males and one segmented in female. Male parameres asymmetrical, small. Female with short gonapophyses. Morphology: Size: Males attain a length of 3.6-5.2 mm and females may attain a length of 4.6-5.8 mm. Maximum body width of male (across middle) 1.27mm and of female 1.43mm.

Nychia sappho
Description: Dorsally entirely white with dark reddish eyes. Females are wider than male. Males are slender in appearance. Head length 0.612mm, head with vertex a little raised. Antenna three-segmented, hidden inside a groove ventrally.Eyes holoptic, united basally, length of eye 0.71mm and width 0.59mm. Interocular region narrow, width 0.18mm.Rostrum 1.03mm in length, dark brown in colour. Males are with rostral prong in the second rostral segment. Pronotum 1.56 times wider than length (W/L=1.24/0.79), short and trasverse with concave angles. Hemelytra translucent. Scutellum small, 0.87mm in length and 0.59mm in width, hemelytra without clavus and sutures. In females, hemelytra fully covered the body, while in males, body remains uncovered. Length of abdomen 2.21mm, width 0.69mm.Ventral abdominal keel not extending upto the

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S. Basu, in wet preservation, Zoological Survey of India, Kolkata.
Description: Small, robust species, more or less dark species. Eyes reddish brown, vertex yellowish brown in colour. Pronotum medially with a pale transverse band, posteriorly hyaline appearing brown to black. Scutellum yellowish brown. Head dorsally rounded, 0.67mm in length and width infront of eyes is 0.48mm. Anterior width of vertex slightly produced. Synthlipsis just less than half the anterior width of vertex. Length of eye 0.97mm and width 0.84mm. Interocular width 0.58mm, less wide than eye width. Pronotum 0.66mm in length. Humeral width 2.21mm, lateral margins of pronotum diverging, posterior margin almost straigth. Rostrum 1.54mm in length. Both sexes have a slight depression on anterior surface of hind femur near to trochanter. Hind femur with a nodule distally. Mesotrochanter as in Image 31g. Ventrally, metaxyphus as in Image 31e. Abdomen 2.58mm in length, 1.58mm in width, tapering towards the end.
Genitalia: Male paramere pear-shaped, concave along outer margin. Female ovipositor long, stout, and sometimes reaching little beyond the end of abdomen. Morphology: Size: Female body length ranges from 6.7-7.5 mm. Male attains a length between 7.5-8.0 mm. In both sexes, maximum width ranges within 2.3- 2.75 mm. Description: Small pale species. Eyes pale reddish brown. Vertex with a black stripe along inner margins. Anterior part of pronotum yellowish brown, posteriorly appearing dark brown to black. Scutellum yellowish brown. Abdomen ventrally black. In dorsal view, head rounded. Anterior width of vertex slightly produced. Head length 1.1mm and width 0.81mm (infront of eyes). Pronotum 0.90mm in length. Humeral width 2.54mm. Scutellum 1.56mm in length, 1.67mm in width. Interocular width 0.72mm. Eyes 1.2mm in length, 0.83mm in width. Pronotal posterior margin convex, centrally emerginated. Hind femur (2.41mm) longer than the mid femur (1.43mm). Hind femur distally with two spines as in Image 32d. Mesotrochanter rounded. Claw of mid leg is curved, stout. Length of abdomen 2.85mm and width 1.94mm, ventrally hairy, and with a prominent keel. Metaxyphus as in Image 32g, elongated, apically convergent.
Genitalia: Male parameres short and triangular. Female ovipositor prominent and elongated.
Global distribution: Sumatra, Java, India Distribution in India: West Bengal Habitat: Small pools with rich vegetation and muddy bottom, and stagnant pools within forests.
Remarks: This species is a new record in India. It is almost distinguishable from Enithares mandalayensis, by the male chaetotaxy of mid leg, metaxyphus of both sexes, and male genitalia. It is quite possible that Enithares unicata is only a geographic race of E. mandalayensis.

Family Pleidae Fieber, 1851
Body minute (size 1.5-3mm), compact, with strongly condensed body, swimming upside-down, somewhat resembling miniature notonectids, having the head and thorax not fused. Because of their small size, they may escape notice of collectors. The head relatively large, directed ventro-caudad; rostrum short and threesegmented. The abdomen has a distinct midventral carina.  Description: General body color yellowish brown to dark brown. Eyes reddish brown. Scutellum yellowish white. On the vertex two pale brown oval spots present. Head pattern consists of two pairs of dots dorsally of the median stripe. The head marking pattern, however, may be vague or absent except for the median stripe. Frons and vertex finely punctuate. Interocular width almost twice the width of an eye. Pronotum wider than long, lacking the characteristic well-defined dots at humeral angles and posterior margin. Hemelytra with very fine hairs, coarsely reticulately punctuate. Metasternal keel with a more or less irregular anterior margin and a shallow depression at middle. Abdominal sterna with three distinct backwardly directed keel.
Genitalia: Male genital segments modified. Seventh male sternite obtuse or with a small notch. Male parameres as in Image 33h, with several setae. Seventh female sternite with small acute tip. Female ovipositor (Image 33g) with numerous spines, the number ranges from 14-17 in right ovipositor and in left ovipositor, the

Genus Ptilomera Amyot and Serville, 1843
Diagnosis: Large, robust, stout water striders. Body colouration dark brown to yellowish brown or dark green, with areas of black markings covered by silvery pubescence, ventrally pale yellow to white. Head anteriorly widened infront of eyes with antennal tubercles divergent anteriorly. Eyes large, reddish brown or black, broadly rounded. First antennal segment longer than the combined length of II-IV. Rostrum short with two long sensory setae on posterior margin of segment III, not reaching beyond the prosternum. Pronotum in apterous forms sub-quadragular in shape, wider than long, posterior margin of pronotum straight to weakly concave. Metanotum shorter than mesonotum, with median longitudinal depressed black midline. In macropterous forms, pronotum is greatly enlarged. Fore wing with distinct venation. Forelegs enlarged with femur straight, weakly incrassate, longer than tibiae, fore tibiae slender, with spur on inner margin at apex, fore femur and tibia with a few small black tubercles along inner margin. Male mid femur bearing a fringe of stiff black setae, which is absent in females. Male abdominal tergite VIII greatly enlarged and conspicuous. Proctiger expanded, often with lateral wings. Pygophore elongated.Parameres large, curved, bearing fringe of long setae. Female genital segments with well-developed connexival spines. Description: Length of head 1.16mm, width across eyes 1.52mm, interocular width (0.75mm) 1.66 times wider than the eye width (0.45mm). Eyes 1.7 times as long as width (L/W=0.78/0.45), head infront of eyes little swollen, with a few trichobothrial setae. Vertex with a pair of backward angling dark spots on either sides of midline, interocular region with a pair of vertical dark band parallel to the margin of eyes, and with a few silvery setae. Antenna dark brown with silvery pubescence, first antennal segment longer than the length of rests together, length of antennomeres, 1-4: 5.29mm, 1.16mm, 2.01mm, and 1.32mm. Rostrum 1.55mm in length, extending upto the margin of fore coxa, third segment of rostrum covered with short recumbent silver setae. Pronotum 1.1mm in length and 1.7 times wider than length (width 1.91mm), with a cavity-like dark patch present medially, a shallow transverse sulcus starting from posterior margin of pronotum reaching up to the margin of humeri. Humeral width 2.76mm, posterior margin narrowly flattened, evenly curving, demarcated by a shallow curving sulcus. Wings uniformly pale brown with prominent dark venation, extending beyond the posterior tip of abdomen. Abdominal tergites 2.8 times longer than the width (L/W=4.36/1.53), tergites II-VII dark brown with small silvery setae and a median yellowish patch. Connexiva prominent, dark brown, about one fourth as wide as abdominal tergites. Fore trochanter with four prominent setae, fore leg 6.01mm in length and 0.71mm in width, with a dense hairy black patches towards its inner margin basally and with a few setae distally, two small tooth present near tibial margin. Fore tibia with two small tooth followed by a small curvature, marked with another small tooth towards its anterior margin; outer and inner margin with rows of hairs. Fore tarsae two-segmented, hairy with a pair of sharp, curved claws. Mid and hind legs with thick upright black

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setae throughout, mid femur with swimming hair fringe posteriorly. Metacoxal spine absent. Genitalia: Abdominal sternite VIII broadly elongated, clothed with short black recumbent setae dorsally, length 1.65mm and width 0.95mm. Seventh abdominal segment of male short. Pygophore (Image 35l) small, simple and broad, the lateral lobes of pygophore slender and hidden inside except their tips, without dorsolateral projections. Male proctiger as in Image 35k. Paramere as in Image 35m, apex sharp, but ends bluntly. In female, seventh abdominal segment simple, without prominent connexival spines.

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of female with rear margin not broadly rounded. Base of connexival spine arising from beneath the dorsal edge of seventh connexivum, the transverse base of connexival spines overlapping the rear margin of seventh abdominal segment on either side. Connexival spines long, their tips attaining the tips of dorsolateral lobe.
Global distribution: Nepal and India. Distribution in India: Sikkim, West Bengal, Assam, and Himachal Pradesh.
Habitat: Hill streams, rivers, and waterfalls. Remarks: During monsoon in North Bengal, this species is found abundantly in hilly areas.

Genus Heterobates Bianchi
Diagnosis: Dorsally dark black, clothed with short silvery pubescence. Head with a median black spot and marginal yellowish area. Pronotum with or without median longitudinal yellow stripe. Antenna about as long as body length in male, but shorter than body in female, first segment longer than the rests together. Rostrum stout and densely clothed with hairs. Mesonotum has distinct median longitudinal sulcus. Fore femur sparsely clothed with long hairs on inner margin, fore tibia with a conspicuous process at inner apical angle. Mid tibia with fringed hairs basally, first mid tarsal segment longer than the second, without claws. Hind tibia strongly curved apically, with inconspicuous fringe of hairs on entire inner margin. Male genital segment VIII with dorsal apical margin rounded. Pygophore well-exposed, narrowly rounded on apical margin. Connexivum slanting towards middle basally in female, each abdominal tergites in female becoming progressively larger posteriorly. Seventh segment of female broadly rounded on dorsal apical margin.
Heterobates rihandi (Pradhan, 1950 Morphology: Size: Body length of male ranges from 6.8-7.1 mm and females may attain a length of 7.0-7.4mm. Description: Body black dorsally. Head pale brown with a central longitudinal spot extending from its anterior end to the vertex, the central spot at its posterior margin deeply emerginate. Antennal tubercles tipped with black. First antennal segment much longer than the other threesegments together. Head 1.9 times as long as wide (L/W=0.85/ 045). Eyes large, prominent and casteneous. Length of eyes 0.46mm, width 0.22mm. Rostrum 1.47mm in length, four-segmented, not passing beyond anterior coxae, third segment longest than others. Pronotum shining black with an inverted 'T'-shaped pale yellowish brown markings touching the posterior margin. Length of pronotum 0.58mm and width 1.02mm. Meso and metaotum shining black with silvery grey pubescence, provided with a central longitudinal yellowish brown marking at middle. Abdomen three times longer than wide (L/W=2.75/0.9). In male, abdomen black with yellowish brown genital segment. Fore femora pale yellowish brown, distinctly longer than tibia. Fore tibiae with a distinct apical spine-like protuberance. Mid tibiae fringed with long swimming hairs inwardly.
Genitalia: Male genital segment 0.62mm in length and 0.46mm in width and bluntly acuminated towards apex. Male paramere as in Image 39n. Male proctiger broad, lateral margin little pointed outward (Image 39k). Female genital segment elongated, more or less W-shaped. Sixth abdominal tergite widest, terminal segment pale ochraceous, short, with a few short fine bristles at its posterior margin. Female connexival spines long and pointed.
Global distribution: India. Distribution in India: Uttar Pradesh, Arunachal Pradesh, Himachal Pradesh, and West Bengal.
Remarks: This species is a new record to West Bengal. They are mostly found hiding between cobbles. They possess a distinctly demarcated flattened body ventrally, which helps them in adhering to the stones or in beds of fast-flowing hill streams.

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Fore femur dorsally with two broad black stripes, one on anterior margin and another about one-fifth from posterior margin, both confluent near apex (Image 40c), ventrally without prominent stripe, apically margined with piceous hue. Flexor side of femur with 9-11 setose spines, apex with three minute spines in addition to fringe of setae. Ventral region of mid trochanter with 2-5 denticles. Fore claws absent. Hind trochanter at posteroventral region with one to three thin short brown spines, femur at base of inner margin with three thin erect hairs, apex of femur with few stout spines. Dorsal length of abdomen of male 2.28mm, abdominal venter densely clothed with silvery white hairs. Anterior margin of tergite I distinctly convex and posterior margin distinctly concave (Image 40e), anterior region of sternum VIII with transverse depression. Genitalia: Proctiger very broad at base, suddenly narrowed beyond midlength, clothed with dense hairs (Image 40j). Pygophore with W-shaped median notch at base, its apical part produced into tongue-like lobe, clothed with minute hairs, posterolateral region of basal part blunt in lateral view (Image 40g). Paramere basally stout, curved before middle, outer margin beyond middle curved, apical part with pilosity, tip blunt and slightly bent to middle (Image 40h), visible externally at abdominal tip. Dorsal sclerite of endosoma deeply split anteriorly and basally (Image 40i). Connexival segment VI with long, tubular, yellowish brown process clothed with numerous short hairs, first gonapophysis (G-I) with several long setae basoventrally on both sides and with numerous medium-sized setae dispersed throughout ventral region; apically with a thorn-like blunt process, length of process I (GP-I).
Global distribution: India. Distribution in India: West Bengal.
Habitat: This species is found in the shady areas of slow-flowing rivers or streams.

Remarks:
The males of Pleciobates bengalensis Jehamalar, Basu & Zettel, 2014 can be easily distinguished from the most closely related species, P. expositus, by a prominent silvery white fascia on each side of the sublateral region of the mesonotum, the straight posterior margin of abdominal tergite VII, the concave posterior margin of tergite VIII, and the structure of endosomal sclerites.

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Genus Chimarrhometra Bianchi, 1896 Diagnosis: Body elongated, dorsally yellowish to reddish brown with black or brown markings. Venter pale in color. Head directed forward with small distinctly visible antenniferous tubercles. Eyes large, globular. Antennae slender, shorter than the body, first antennal segment distinctly longer than the other segments, without spine-like hairs. Rostrum stout, reaching hind margin of prosternum. Pronotal lobe completely reduced in apterous forms. Fore femora incrassate in male. Hind legs much shorter than the mid leg. Hind tarsae shorter than mid tarsae, claws long, Morphology: Size: Body length of male 3.12-3.3 mm and body length of female 3.46-3.52 mm. Max body width of male 0.95mm and of female 1.24mm.
Description: Body dark black with distinct yellowish orange markings. Length of head 0.61mm and width 0.39mm, head directed forward, with median lyreshaped markings and two sub-lateral streaks. Antennal tubercle small, but visible from above. Length of antennal segments 1-4: 0.68mm, 0.56mm, 0.63mm, 0.72mm. Interocular width 0.39mm. Eye length 0.32mm and width 0.18mm, eyes large and globular, red in colour. Length of pronotum 0.39mm and width 0.83mm, pronotum anteriorly with two median and two sublateral longitudinal stripes. Metanotum and abdomen dorsally dark, marked with yellow markings. Mesopleura with longitudinal dark stripe, venter pale yellow, marked with one median and two sublateral dark markings. Metasternal process is sub-triangular and centrally longitudinally sulcate. Male fore femur relatively slender, with two separate hair tufts beyond middle. Mid femur relatively long. Length of abdomen 1.11mm and width 0.69mm.
Genitalia: Length of female genital segment 0.58mm Habitat: Jungle streams, pools, puddles near river banks or stream beds.

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Bengal.The females are difficult to identify without associated males.
Description: Black with prominent yellowish orange markings and silvery dots dorsally. Head little broader than long, yellowish with a roughly V-shaped black mark medially, a pair of black elongated spots near the inner margin of eyes. Interocular region 2.4 times longer than eye width (interocular width/eye width=0.44/0.18). Antennal segments spiny, antennomere 1-3 almost equal in length, length of antennal segment 1-4: 0.78mm, 0.74mm, 0.75mm, 0.86mm. Rostrum 1.40mm in length, surpassing the fore trochanter. Pronotum with a roughly W-shaped yellow mark, laterally connected to the propleural stripes. Mesonotum and metanotum also with a prominent broad W-shaped yellow mark, wider than head.Certain individuals with middle arm of this 'W' disconnected from remainder of the two arms. Genital segments (tergite VIII) black with three triangular, small yellowish markings anteriorly. Mesonotum and metanotum 2.9 times longer than pronotum. Fore femur with three hairy black patches located almost equidistantly, followed by a shallow curvature distally. In some specimens, the last two black hairy patches connected with a median hairy zone distally, where as some lack this continuation. Fore leg of female relatively simple, without any markings (Imaeg 43c). Middle femur 2.5 times as long as fore femur and 1.1 times longer than hind femur. Fore tibia hairy, basally with an indentation. Tarsus with a pair of prominent curved claws. Abdomen including genital segment 1.3 times longer than the width (length/ width=0.91/0.72).
Genitalia: Sternite VIII of male, 1.3 times longer than width (length/width=0.96/0.7), almost rectangular with its curved lateral arm of proctiger projecting outward in some individuals, however, in others, this is hidden within the genital segment. Pygophore widened basally on ventral view, but tapering distally, with scattered long hairs medially and densely arranged hairs along its margin. Proctiger shaped as roughly arrow-shaped, outer margin curving inward. The lateral arms of proctiger long, slender curved at middle, distally almost straight, weakly narrowed towards truncated apex (
Description: Brownish black with yellow markings dorsally. Head yellowish with black markings, 1.2 times wider than long, length of head 0.57mm, width of head across eyes 0.71mm. Interocular width 0.42mm. Eye reddish brown. Antennae shorter than body-length, length of antennomeres 1-4: 0.76mm, 0.74mm, 0.78mm, 0.86mm. Pronotum 1.8 times wider than length (W/L=0.87/0.48), black with yellow marking as typical for the genus. Metanotum almost black, with silvery pubescence, posterior margin sinuate. Male fore femur (Image 45d & e) moderately incrassate, ratio of length and width 4.1 (0.99/0.24), with three black tuft of hairs, basal part with elongated patch of stiff sub-erect hairs, followed by one thin almost pointed patch of hairs and distally with one elongated patch of black, short hairs. Fore tibia modified with outer margin concave and inner margin with a prominent ridge near middle, covered with short dense pilosity. Fore tarsus with first segment shorter than second segment; claws sharply bent, curved. Fore leg (Image 45f) of female relatively slender, dorsally with a black stripe, ratio of length and width 5.9 (1.18/0.20), inner margin of fore femora with densely arranged black hairs and with golden hairs distributed throughout. Mid leg longer than the hind leg. Mid and hind femur, tibia, tarsus with scattered spines.Abdominal tergite II-IV entirely black, V-VIII black with a median yellow spot. Meso-and metaacetabula with silverish, shining, frosted areas, sterna II-VI combined; sternite VII little wider and longer than the rest.
Genitalia: Abdominal sternum VIII 1.4 times as long as wide (L/W=0.69/0.48), elongated, with silvery pubescence. Pygophore and proctiger as in Image 46m & n. Pygophore oval-shaped, basally more widened, with densely arranged long hairs and modified distally into an elongated narrow process. Proctiger semi-circular in shape, hairy below. The lateral arms of proctiger bifurcated at middle forming two slender arms, tip of these two bifurcations end bluntly. In dorsal view, it is widened anteriorly, and then gradually narrowed towards its posterior end (Image 46o & p). Female sternum VII 1.28 times as long as wide (L/W=0.73/0.57), basally broad, traphaezoid, hairy below. Ovipositors (Image 45j) are long with densely arranged spines on it. Proctiger of female round shaped, ends bluntly.
Global distribution: India.  Basu, Subramanian and Polhemus, 2014 is closely related to A. dentata Polhemus and Andersen, 1984, first described from Dehradun, Uttarakhand.

Genus Onychotrechus Kirkaldy, 1903
Diagnosis: Body small, elongated. Head typically with amedian, longitudinal yellowish brown stripe. Pronotum black with a median and two sub-lateral stripes. Venter pale yellowish. Head projected forwards with prominent antenniferous tubercles. Eyes large, globular. Antennae longer than body, first segment of antenna longer than the second with two closely set dark spine-like hairs in apical third and usually another two spine-like hairs beyond that. Pronotal lobe reduced in apterous forms, but macropterous forms having distinct humeri. Fore femora usually slender, may or may not be modified apically in male. Mid and hind legs sub-equal in length. First tarsal segment shorter than the second, with ventral row of spine-like hairs. Males with abdominal venter about one-fifth of body length and more or less distinctly grooved medially. Male genital segments small. Claspers relatively small, club-shaped with short setae. Endosomal sclerite welldeveloped with long lateral sclerite. Female sternum VII partly exposed ventrally.

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maximum body width across mesoacetabula 1.38mm. Description: Body dorsally black with yellow markings. Head with a median yellow longitudinal stripe, which ends in a blunt arrow head (Image 47c), head length 0.64mm, width 0.41mm. Interocular width two times as large as eye width (0.45:0.22). Eye length 0.44mm. Length of antennal segments 1-4: 0.96mm, 0.94mm, 0.89mm, 1.38mm, first antennomere with three spines distally, of which two spines are long, third one small and arising near base of first spine.Pronotum with two broad yellow sub-lateral stripes, a thin median yellow stripe, and two yellow curved lateral stripes. Pronotum length 0.53mm, width 0.79mm. Meso and metanotum with two thin lateral stripes, two broad sub-lateral stripes and an indistinct short yellow median line. Mesosternum (Image 48f) modified, with narrow median groove slightly widened posteriorly, depression with black, scattered setae directed to its centre. Forefemur (Image 48h) slender, widened basally, but almost evenly tapering apically, length of forefemur 1.17mm, width 0.25, apically with a few setae and with short dark stiff hairs distributed throughout, yellow with one broad dark band on dorsal side and one very slender dark brown band on extensor side. Foretibia (Image 48i) strongly curved, basally with patch of few short hairs on flexor side, a soft spinous structure protruded outwards from base of curvature; apical region with two prominent black spines that diverge from almost touching bases (forming a 'V'), and with four black spines and a row of short hairs towards extensor side. Mid and hind femora slender, both with distinct rows of short spines arranged equidistantly. Fore claws (Image 48k) sharply bent and slightly longer than mid and hind claws. Abdominal tergites completely black (Image 47d and Image 48l). Abdomen (Image 48l & m) short, only about one-third of body length. Length of abdominal sternites 1.01mm, width 0.90mm. Sterna II-VI visible as very narrow curved strips, sternum VII (Image 49p) much longer.
Genitalia: Pygophore sub-oval, little elongated, widened basally. Proctiger (Image 49r) short, widened distally, gradually tapering towards basal part, with long setae and medially with numerous punctures.   Subramanian, Basu & Zettel, 2014 is a close relative to Onychotrechus jaechi recently described from Bhutan. They share some common characteristics such as males of both species have almost identical pro-, meso-and metasternal markings, basally incrassate fore femora, similar mesosternal modifications and short abdominal segments.

Genus Gerris Fabricius, 1794
Diagnosis: Body small or medium in size, length varies from 5.0-15mm. Wing dimorphic species. Head elongated with prominent markings. Antennae are short and shorter than half of body-length, first antennal segment without spinous hairs, distinctly shorter than the second and third segment together. Fore femora usually pale and with longitudinal dark stripes, thickened. Metasternal scent orifice slit-shaped and tuberculated. Hind femora sub-equal or shorter than mid tibia. Posterior corners of abdominal connexiva triangular and pointed, but not spinous, except in a few females. Phallotheca of male well-sclerotised ventrally.
Genitalia: Abdominal segment VIII 1.7 times as long as wide (L/W=0.98/0.55). Ventrally, segment VIII with a pair of impression, furnished with silvery hairs. Endosomal sclerites in dorsal view as in Image 50i.

Distribution in India:
Arunachal Pradesh, Jammu and Kashmir, Sikkim, Uttar Pradesh, and West Bengal.
Habitat: Slow-flowing streams, stagnant water bodies with good vegetation.
Remarks: This species is most frequently encountered in apterous forms.
Description: First antennal segment nearly half in length than the remaining three segments. Small brownish yellow spots infront of each eye. Anterior lobe of pronotum distinct, a mid longitudinal carina present on pronotum, anterior margin of pronotum with a pair of prominences. Mesothorax with short, erect pubescence laterally. Abdominal sterna of male usually with a distinct longitudinal keel.
Genitalia: Abdominal segment VIII with paired, oval impressions usually furnished with silvery hairs ventrally. Dorsal plate of endosomal sclerite with subparallel sides, almost slightly prolonged beyond the dorsal sclerites (Image 51i). Hind margin rounded. Distal recurved part of dorsal sclerite shovel-shaped and widened. Ventral sclerites paired small, almost rudimentary. In female (Image 51g), connexival spines distinctly pointed, almost reaching posterior margin of last abdominal segment.
Global distribution: China, Japan, East of Russia, Korea, Bhutan, and Taiwan. Distribution in India: Sikkim, Uttar Pradesh, West Bengal, Arunachal Pradesh, and Assam.
Habitat: High altitudinal hill streams or stagnant pools within high mountainous forests.
Remarks: This species is mostly found in the high altitudinal area of northern India. They encountered mostly in macropterous forms.

Genus Aquarius Schellenberg, 1800
Diagnosis: Body large in size, ranges from 10. 4-26.5mm. Pronotum usually dark with median pale stripe anteriorly. First antennal segment long, sub-equal to or longer than second and third antennal segment together. Fore femora uniformly dark. Well-developed connexival spines at abdominal end. Hind tibia being more than four times as long as first hind tarsal segment. Male genital segment long. Pygophore large, sub-ovate. Proctiger tapering with more or less pointed apex. Parameres small, setose. Morphology: Size: In macropterous male, body length ranges from 11-12.5 mm, maximum body width (across mesoacetabula) 2.5-3.0 mm. Body length of macropterous female 11.9-12.2 mm and maximum body width 2.8-4.0 mm.Brachypterous male attains a length of 10.5-10.7 mm, maximum body width 2.5-2.6 mm.

Aquarius adelaides (Dohrn): Image 52. a-f and
Description: Dark brownish dorsally. Pronotal lobe with entire margin brownish yellow. Body elongated with distinctly visible connexival spines. Antennae 6.25mm in length, third segment much shorter than the second and a little shorter than the fourth segment, first antennal segment nearly as long as remaining three segments together. Pronotum with a distinct black carina on posterior lobe of pronotum. Rostrum reaching the posterior margin of prosternum. Fore femora almost straight and slightly constricted before apex, terminated by two distinct spines. Mid femur ventrally with pilosity and numerous spines. Hind femora distinctly longer than the body length. Metasternum slightly depressed posteriorly, with slit-shaped scent orifice. Abdomen moderately slender.
Genital segment: In male, connexival spines stout and long, almost reaching abdominal end. However, in female, the connexival spines are stout and surpass the abdominal end. Second abdominal sternum long, whereas 3-7 sterna sub-equal in length, slightly depressed. Posterior margin of seventh sternum deeply emarginated with a broad, triangular impression in middle. Genital segment VIII sub-cylindrical with prominent triangular tubercle ventrally. Pygophore large, paramere with setae and conate. Dorsal plate of

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Tamil Nadu, Uttar Pradesh, and West Bengal. Habitat: Fresh water habitats like fish ponds, lakes, temporary pools, and flooded paddy fields.
Remarks: This species is widely distributed. They can be collected from larger stagnant waterbodies. This species is closely related to Aquarius paludum, but can be distinguished by male genital segment with a very prominent triangular tubercle on ventral surface and the structure of endosomal sclerite.

Genus Neogerris Matsumura
Diagnosis: Body elongated. Dorsally dark black, venter pale. Head typical with U-shaped yellow band. Pronotum with yellow oval or round spot anteriorly, pronotal lobe dark with yellow margins. Head directed forward. Eyes large, globular with two short trichobothria. Antennae short and robust, first segment shorter than or sub-equal to the second and third segment together, fourth little longer than the third. In macropterous forms, pronotal lobe wider than long. Forewings with two closed cells apically, without any distinct vein. Fore femur with diversified ventral pubescence comprising of short, dense hairs and with long bristles. Fore pretarsal claws well-developed, mid and hind claws totally reduced. Abdomen moderately shortened in most species. Connexivum not terminating in spine. Male genital segment slightly elongated than in female. Male pygophore simple, sub-rectangular. Proctiger narrow. Claspers very small, symmetrical, devoid of hairs. Female sternum VII with produced hind margin in middle.
Remarks: They are mostly found as winged individuals and are reported as the predators of the brown plant hopper and serves as bio-control agents.

Genus Rhagadotarsus Breddin
Diagnosis: Body black dorsally. Head along eyes reddish. Pronotum yellow to orange yellow at middle. Head with an obscure median longitudinal sulcus or sometimes without it; posterior margin of head concave. Antennae slender, first segment much longer than second, second shorter than the third, and fourth segment about as long as third or longer. Pronotum very short, basal margin concave laterally rounded. Metasternum slightly depressed anteriorly, posterior

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margin concave. Fore femur slender, without any modification in both sexes, apically slightly thickened. Abdomen long, nearly straightly narrowed posteriorly. Connexivum strongly reflexed. Male seventh sternite longer than sixth sternite, with a deep depression.

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modified; deeply excavate basally, depression deeper and hair free medially. Connexiva broad. Endosoma as in Image 57i. Proctiger (Image 57g) narrow and elongated. Pygophore as in Image 57h. Female genital segment with a median ridge, with a serrated ovipositor in seventh segment (Image 57f). Global distribution: Malaysia, Singapore, Java, Indonesia, Sri Lanka, Thailand, Vietnam, China, Myanmar, Taiwan, and India.

Remarks:
The food habits of Rhagadotarsus are almost same as most gerrids -any insects trapped in the surface film of water. They are feeble swimmers.

Genus Metrocoris Mayr, 1865
Diagnosis: Body colouration yellowish to light brown, with black markings on dorsum. A longitudinal marking on the interocular space of head. Males are usually larger than the females. Body dorsally subtriangular, dorso-ventrally flattened, covered with short dine sparse black hairs. Head blunt, projecting infront of eyes.Pronotum of macropterous forms enlarged. Propleura clothed with dark bristle-like hairs. Metasternum reduced to small, triangular sclerite. Abdominal tergites with some golden pubescence. Male abdominal sternum VIII longer, broadly concave. Female abdominal sternum VII strongly developed and apically modified. Male fore femur may be incrassate or moderately incrassate or sometimes slender, with or without indentations, constrictions and teeth. Female fore femur slender, without any modification. Male genital segment elongated and large. Parameres usually large and sometimes visible from outside in some species.

Morphology:
Size: Body length of apterous male 7.5-7.6 mm and width 3.35mm. Apterous female attains a length of 5.2mm and width 3.1mm.
Description: Interocular dark mark arrow-head shaped, bifid posteriorly. Head, pronotum with distinct markings. Antennae brown with the first segment yellowish basally. Abdomen blackish dorsally. Venter yellowish. Head 1.89mm in width. Interocular width 0.75mm. Pronotum bulbous in male, distinctly broader than head, width of pronotum 1.96mm. Male fore femur (Image 58c & d) strongly incrassate, apical third constricted but without ventral indentation, a bipartite sub-apical tooth. Inner margin of fore tibia with a sharp sub basal tooth-like elevation. Female fore femur slender. Mid femur longer than hind femur.
Genitalia: Male genital segment VIII (Image 58e & f) long, length 1.62mm and width 1.16mm. Pygophore prolonged ventrally, constricted before apex. Proctiger long and narrow. Paramere large and hook-like, extending beyond genital segments laterally and with blunt apex. Endosomal sclerite well-developed. Dorsal sclerite long and curved apically. Female genital segment VII large, apical half broadly lobed, and with a median notch, strongly curved upward.

Morphology:
Size: Body length of apterous male 4.9mm and body width across mesoacetabula 2.29mm. Apterous female attains a length of 4.1mm and body width across acetabula 2.18mm.
Description: Dorsal body coloration yellowish to orange with dorsal black markings. Interocular dark mark on head arrow-shaped, bifid posteriorly, posterior margin connected with dark margin of eye on each side. Head width subequal to pronotum width. Head length 0.68mm, width 1.46mm. Eyes 2.3 times longer than broad, length 0.72mm, width 0.31mm. Interocular width 0.56mm. Posterior half of eyes covering propleura by 0.32mm. Length of antennal segments 1-4: 2.09mm, 0.80mm, 0.57mm, 0.49mm, second segment slightly

Water bugs of Himalayan and sub-Himalayan regions of West Bengal
Basu et al.

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longer than third. Rostrum reaching upto forecoxa, length 1.32mm. Pronotum bulbous, 2.6 times broader than long. Pronotum length 0.54mm, width 1.44mm. Meso-and metanota 1.2 times broader than long. Male fore femur strongly incrassate, stout, broad, with dorsally broad black median elongated marking, in some individuals the markings extending attaching to the rectangular markings distally, marked with subapical indentation, bearing a more or less sharp subapical tooth followed by a bidentate tooth near distal margin, visible in both dorsal and ventral view. Fore femur hairy near distal margin, ratio of length/width 3.5 (length/ width=2.05/0.58). Fore tibia modified, with a strong curvature basally, bearinga small pointed tooth near

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distal margin. Fore trochanter with three long setae. Fore, middle, and hind tibiae and tarsi with dark pilosity. Abdomen length including genital segments 1.91mm (along midline). Genital segment 1.1 times longer than broad, covered with dense short hairs anteriorly and long hairs posteriorly. Genitalia: Segment VIII large and with dense pilosity, bearing two broad black semi-circular markings separated by distinct gap, almost covering genital segment. Length of genital segment VIII 0.92mm.

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segments 1-4: 2.48mm, 0.89mm, 1.16mm, 0.86mm. Rostrum length 1.72mm, reaching fore trochanter. Pronotum 3.3 times as broad as long (width 1.52mm, length 0.45mm). Pronotum slightly bulbous. Meso-and metanota slightly broader than long (width 2.78mm, length 2.53mm). Fore femur slender, ratio of length/ width 6.87, with slight curvature marked with small, prominent apical tooth and long hair fringe distally, two long setae basally, inner margin with a row of short hairs. Inner surface of tibia hairy, without indentation but with several small spines arranged equidistantly from base to apex. Genitalia: Male abdominal tergite VIII subquadrate, length 0.61mm, width 0.63mm, densely covered with black and golden short stiff hairs. Pygophore broader than long. Proctiger elongated, convex medially on both sides, with small, angular lateral lobes, clothed with dense hairs. Parameres symmetrical, projecting prominently from genital segment, sickle-shaped, outer margin sinuate, apex expanded to form small head, tip rounded. Female sternumV with medially invaginated apical margin, sternites II-IV with dense thick hairs medially and the density reduced laterally towards the margin. Sternum VII elongated, bilobed, laterally constricted basally, fringed with golden short hairs and with concave apical margin.
Description: Dorsally body yellowish orange with distinct black markings. Interocular area with broad arrow shaped marking medially. Head length of male 0.74mm and width 1.54mm.Pronotum wider than long, length 0.553mm and width 1.59mm. Fore femur strongly incrassate, ratio length/width=3.22(2.68mm/0.83mm), constricted in apical third, with bipartite apical tooth, without any ventral indentation. Fore femora of female slender, with long stout hairs at basal half. Length of abdomen 2.87mm and width 1.62mm, abdominal tergites black with dense golden pubescences.
Genitalia: Male genital segment VIII elongated, large, rectangular in dorsal view, length 1.45mm and width 1.04mm. Dorsally pygophore prolonged and sub apically constricted, with straight apical margin. Proctiger long distally narrowed. Paramere long, hook shaped, pointed apically. Female genital segment VII with large medial lobe, with longitudinal ridge laterally from anterior end of hind margin and with small wing shaped lobes, medial lobe sub-trapezoidal, with distinctly notched posterior margin. Description: Dorsal body coloration yellowish to orange with distinct black markings. Interocular dark mark on head rectangular, bifid posteriorly, posterior margin connected with dark margin of eye on each side. Head length 0.64mm, width 1.46mm. Length of antennal segments 1-4: 2.0mm, 0.77mm, 0.73mm, 0.61mm. Rostrum reaching beyond forecoxa, length 1.61mm. Pronotum slightly bulbous, 2.8 times broader than long. Pronotum length 0.51mm, width 1.45mm. Male fore femurslender and hairy, dorsally black and ventrally with black median elongated marking, basally yellow, without any modification, but with a slight invagination near middle. Fore tibia without any modification. Fore femur of female slender, elongated, without any modification. Female hind trochanter with a pointed apex bearing a distinct, tapering tuft of long hairs.
Genitalia: Segment VIII in male elongated and with dense pilosity, lateral margins with few long setae. Pygophore prolonged, broad and setiferous. Proctiger prolonged, truncated distally, with distinct dark long setae throughout. Parameres not visible externally, large, stout, curved distinctly in the middle, twisted medially, then broadened and finally tapering slightly towards the truncated apex and the posterior end, with 2-3 setae near middle and several white dots distributed up to apex. Endosoma poorly sclerotised, with dorsal sclerite long, expanded horizontally and recurved proximally; lateral sclerite apically bent a little upward, almost straight, ventral sclerite long, not extending beyond the dorsal sclerite, concave submedially. Abdominal sternum VII of female small, broad and rectangular, hairy, laterally little constricted and with a smooth caudal margin entirely covering rounded genital segments, laterally convex, hairy dorsally.  lateral margin of pronotum. Antennae slender and long, first segment always long, sparsely armed with black bristles. Rostrum short and transverse, both anterior and posterior margins concave, lateral margins rounded. Metanotum without median longitudinal sulcus. Fore leg relatively long and slender, femur with or without a small tubercle on inner margin, sparsely clothed with long hairs. Fore tibia with a narrow inner apical process defined by a depression on both surfaces, tarsus with distinct claws and with arolium. Mid femur armed with spinous bristles sparsely. Hind femora straightly narrowed apically, sparsely clothed with spinous bristles. Abdominal ventrites anteriorly strongly reduced. Seventh segment ventrally a little shorter or longer than all preceeding sternites together. Parameres well-defined. Endosoma with definitive dorsal plate turned black. Female seventh sternite concave on posterior margin. Morphology: Size: Body length of male 2.5-3.5 mm, maximum width across mesoacetabula 1.8-1.9 mm; female body length 2.65-3.7 mm, maximum width across mesoacetabula 1.9-2.1 mm.

Ventidius (Ventidius) sushmae Gupta Image 66. a-h
Description: Dorsally yellowish brown to greenish yellow with black markings. Head with a triangular median spot and a pair of lateral black stripes, head including eyes much wider than long. Eyes rounded on outer margin, covering lateral margin of pronotum. Rostrum short, surpassing hind margin of presternum. Pronotum short, lateral margin rounded and anterior and posterior margin concave. Metacetabulam broad, with postero-lateral angle simple. Metasterum highly reduced and represented by a small transverse subtriangular plate. Fore leg (Image 66d) relatively simple, long, not clothed with long hairs on inner margin. Morphology: Size: Body length of male ranges from 10.2-11.4mm. Female may attain a length of about 11.2-11.8mm. Maximum body width of male 0.53mm and maximum body width of female 0.65mm.
Description: The general colour of the body brownish yellow. In male, the venter darker in colour, while in female, the venter pale yellowish brown. A narrow white stripe extends along the median line of the body from the posterior margin of eyes to the posterior margin of pronotum. Head 15.9 times as long as the width (L/W=3.03/0.19). Clypeus bluntly conical. Rostrum reaches a length of 2.38mm, reaching beyond the eyes, but not surpassing the head. First antennal segment short, third antennal segmet longer than second. Length of antennal segments 1-4: 0.43mm, 1.10mm, 2.03mm, 0.94mm. Interocular width 0.09mm. Length of pronotum 0.64-0.66 mm and width 0.52-0.56 mm. Length of eye 0.22mm and width 0.12mm. Pronotum with an encircling row of pits parallel to the anterior margin, posterior lobe of pronotum with a median longitudinal row of pits. The hemelytra large and long, extending to the posterior margin of fourth abdominal segments in brachypterous forms. Abdomen 8.9 times longer than width (L/W=4.54/0.51). In male, the length of genital segment 0.59mm and width 0.24mm. In dorsal view, sides of seventh segment of abdomen almost parallel. Fore femora not surpassing the apex of head and hind femora not surpassing the tip of abdomen. The distance between fore and mid coxa 0.86mm.
Genitalia: Seventh sternite of male is transversely depressed and hairy as in the posterior half of sixth abdominal segment. Posterior dorsal margin of seventh segment is fringed with short stiff hairs. The terminal dorsal process of male sharp. In female, the last dorsal abdominal segment broader behind than in front and with a sharp ovipositor.

Genus Mesovelia Mulsant & Ray
Diagnosis: Body slender, attains a length of 2.0-4.0mm. Dorsally yellowish green in colour with some brownish patterns. Head usually distinctly prolonged and deflected infront of eyes. Head length distinctly less than thorax, with three pairs of cephalic trichobothria. Antennae long, slender, with third and fourth segment longer and thinner than first and second segments. Pronotum length shorter or subequal to mesonotum in apterous forms.Macropterous forms having a pair of ocelli on the posterior part of head, while the apterous forms lacking ocelli. The scutellum in macropterous form elevated, fore wings with three closed cells. Legs slender marked with spines and bristles, hind leg long. All tarsae three segmented with two apical claws. The scent gland orifice distinct and situated in tergite IV medially. Male genital segment large. Females are larger than males, with well-developed ovipositor. Description: Body light yellow to greenish in colour. The macropterous forms have two or three closed cells in the forewing, ocelli, while the apterous forms lack ocelli ad scutellum. Head length 0.3mm and width 0.36mm. Interocular width 0.192mm. Eye length 0.145mm and width 0.09mm. Length of pronotum 0.57mm and width 0.63mm. Rostrum long, surpasses the meso coxa and reaching upto midway of body and upto the meta coxa. Length of rostrum 0.82mm. Length of male fore femur 0.50mm and width 0.07mm. Mid femur hairy below and length 0.49mm. In female, mid femur with two, three, or four spines arranged ventrally at inner margin.

Mesovelia vittigera
Genital segment: Length of male genital segment 0.19mm and width 0.18mm, elongated, without any median spine, but with two lateral groups of spines as in Image 70g. The male paramere is prominently curved. Proctiger elongated, apex round. In female, the ovipositor is saw-like and projecting outward. Global distribution: India, Indonesia, Malaysia, Sri Lanka, Thailand, and Vietnam. Distribution in India: Tamil Nadu and West Bengal. Habitat: Freshwater ecosystems like ponds, pools, lakes, and slow-flowing streams with floating vegetation.
Remarks: They are small, slender, greenish bugs, carnivorous in nature, and feed on a variety of dead insects found on water surface. Apterous forms usually outnumber the macropterous forms.

Family Veliidae Amyot & Serville, 1843
Body small (1.8-18mm), oval or elongate bugs. The general colour varies from yellowish brown to grey or black, with dorsum often marked with yellow or brown or silvery spots. Wing polymorphism is common and apterous forms are the most commonly encountered morphs.Presence of pre-apical claws, short legs, and absence of ocelli.

Genus Microvelia Westwood, 1834
Diagnosis: Adults may be apterous or macropterous. Body usually elongate, oval or sub-oval. Colour varies from black or dark brownish above with yellowish brown markings. Body covered with relatively short pilosity. Head shorter than wide, shortly or moderately produced infront of eyes, with a shiny distinct median furrow and a pair of pseudocular pits at base. Antennae relatively long, with small tubercles situated closely to margin of eyes, fourth antennal segments longer than second and third. Pronotum usually longer than head, with large, transverse pale marking or paired spots anteriorly, concave anteriorly, bordered by dark punctures. Macropterous forms having pronotum with distinctly raised humeral angles, the wing reaching abdominal end, long, venation of fore wings forming four closed cells, black with whitish stripes and spots. Fore femora moderately thickened, not modified. Fore tibiae of male with a comb on inner surface near apex. Mid tibiae with long row of curved hairs on inner surface. Claws of mid and hind legs long, slender, with bristle-like arolia. Abdomen relatively long with evenly rounded laterally, depressed or with hair tufts and tubercles. Mid leg distinctly longer than fore leg and shorter than hind leg. Description: Body dull black dorsally with a grayish pubescence. Length of head 0.25mm and width infront of eyes 0.20mm. Head subglobosely arched. Interocular width 0.24mm. Rostrum 0.37mm in length, reaching beyond fore trochanter. Eye length 0.11mm and width 0.06mm, a marginal fascia to head continued inside eyes to base. Length of antennal segments 1-4: 0.07mm, 0.07mm, 0.10mm, 0.16mm. A reddish or yellowish brown marginal fascia on pronotum anteriorly, not reaching the anterior angles. Pronotum 0.39mm in length. Humeral width 0.59mm. Hemelytra spotted with grayish white, of which a large spot present at clavus, corium with two large basal marginal spots, three irregularly shaped spots in transverse series, a large sub-apical spot on membrane and a smaller sub-apical spot at inner margin, lateral margins of width 0.29mm. Length of antennal segment 1-4: 0.43mm, 0.27mm, 0.38mm, 0.35mm. Pronotum 3.68 times wider than long (W/L=0.70/0.19), anterior margin of pronotum black, bearing an orange brown transverse band medially, surrounded by black margins, posterior margin of pronotum either slightly concave or straight. Humeral width 0.84mm. Length of abdomen 1.46mm and width 0.64mm. Mid coxae slightly embrowned. Male mid femur (Image 73f) with three to four slender sharp spines ventrally onbasal half. Male hind femur with 14-18 basal teeth reaching to base of femur, distally followed by seven to nine teeth after the long, curved middle spine. Female hind femur (Image 73h) with three to six basal, one middle, and five to six distal teeth. Hind trochanter with four to six black denticles.

Microvelia (Microvelia) albomaculata
Genitalia: Male genital segment VIII 0.33mm in length and 0.28mm in width. Male paramere (Image 73) short, slightly curved with more or less bluntly pointed apex and with few scattered pegs. Pygophore (Image 73) elongated, broad. Dorsal sclerite as in Image 73. Remarks: It is a wide spread species and distribution ranges from North India to Indian Ocean islands.

Velia (Cesavelia) mitrai
Description: Body color black, with scattered silvery pubescent patches dorsally. Head black with a prominent median furrow, antennae, eyes and legs black. Head length 0.68mm, width 1.10mm. Length of first antennomere 2.2 times head length and 1.4 times head width. Head width 1.8 times as long as interocular space. Pronotum black, with broad patches of silvery pubescence laterally and a transverse orange patch anteromedially. Pronotum length 1.47 times as long as eye length (pronotum 0.59mm, eye 0.40mm). Mesofemur 2.0 times as long as pronotal width. Metatibia 1.0 times as long as metafemur, 1.8 times as long as metatarsus. Second mesotarsus 1.3 times as long as third tarsomere. Flexor side of meso-and metatibia with erect setae. Metatrochanter with eight denticles, fifth and sixth denticles somewhat longer than the remainder. Metafemur of male stout, 6.4 times as long as wide (Image 75 k & l), posterior margin bearing prominent spines (Image 75 k & l), starting with 12 small teeth, followed by two long diverging teeth, continued with 10 small teeth, then another larger tooth, followed by seven small teeth of progressively decreasing size to apex (Image 75l). Metafemur of female slender and slightly longer than in male, lacking spines. Abdominal tergites II, V, and VI with dense patches of silvery pubescence laterally, smaller patches of silvery pubescence present at anterolateral angles of tergites III and IV. Abdominal sternites II-VI dark orange-brown medially. Length of abdominal tergites 4.20mm, maximum width 1.50mm. Connexival spines in male short with apices pointed when viewed both dorsally and laterally. Posterior connexival apices longer than in male, pointed when viewed both dorsally and laterally (Image 74f), covered with short hairs. Genitalia: Male genital segment VIII 1.1 times as long as wide, elongated and hairy below (Image 74g & Image 75i). Proctiger of moderate length, slightly expanded distally with posterior margin broadly rounded, bearing long setae laterally and medially, basal lobes small (Image 75m). Male paramere evenly curved, slightly twisted medially, apex moderately rounded. Endosoma with lateral sclerite relatively slender, expanded centrally, broadly curved along its length (Image 75n).
Ovipositor of female as in Image 75. Global distribution: India. Distribution in India: West Bengal. Habitat: Small, unpolluted, shaded high mountainous streams flowing through forests.
Remarks: This species is closely related to Velia tomokunii Polhemus and Polhemus from Nepal.

Diversity assessment
Estimation of Species richness (Fig. 62) Figure 62 depicts the observed and estimated species richness for the 86 sampling sites of the present study area. Species accumulation curves plotted against sites showed that the slope of the curve rapidly increases in the beginning as new taxa were recorded with increasing number of sites. According to Chao1 mean, a total of 82 species (of which 61 species were identified upto the species level as only nymph or females found in collection) were estimated from the study sites, whereas Jack1 mean and Jack2 mean indicate that the species richness would have exceeded 110 and 122, respectively. This estimated species richness is slightly higher than the observed richness as many of the species of aquatic and semi-aquatic Hemiptera are cryptic in habit and hence might not have been collected during the survey. This trend indicates that there might be a possibility of a few taxa that were missed during the collection because of their ambiguousness or infrequency. The gradual flattening of the curves, however, shows that most of the common and existing taxa would have been sampled and hence can be used as a reasonable estimate of the total species richness for the study sites sampled.

Species richness mapping across the study area (Fig. 63)
Species richness is simply the number of species of a given taxon in unit study area or in the chosen assemblage. This richness measure in ecological study is the most intuitive measure of biodiversity.The current study using GIS mapping tools shows that the Gorumara National Park and Chapramari Wildlife Sanctuary areas of Jalpaiguri are the richest zones as maximum number of species (21-26) occurred in this area. This region is free of human disturbances and is under protected areas. The Lataguri-Kalmati-Baradighi of Malbazar andAlipurduar region is the second highest richness zone showing 16-20 species occurrence. Most of the areas of Darjeeling, including Kalimpong, Rishikhola, Pedong, Mongpu, Mirik, Ghoom, Sonada, Sevoke, Kalijhora, and Gorubathan except Phansidewa-Kharibari-Naxalbari region, shows lowest species richness and only 1-5 species were recorded from this mostly hilly region. The areas of Gajaldoba, Raimatang, Madarihat and Jayanti of Alipurduar region also represents the lowest species richness zone, which may be attributed to the greater degree of anthropogenic disturbances like grazing, pisciculture, dam construction, etc. in the area.

DISCUSSION
The Eastern Himalayan region recognized by the international community as biodiversity hotspots is well represented by a large number and variety of flora and fauna with high degree of endemism. The knowledge on aquatic and semi-aquatic Hemiptera is limited to the taxonomic preliminaries, recording few species from different parts of this region. Little attention has been paid to the faunal documentation of water bugs from the Eastern Himalayan States except the works on the State of Meghalaya (Bal & Basu 1999), Tripura (Bal & Basu 2000), Arunachal Pradesh (Thirumalai 2002), Sikkim (Bal & Basu 2003), Manipur (Bal & Basu 2004), and West Bengal (Bal & Basu 1994) by Zoological Survey of India as a part of their routine survey. In this context, the present study was a pioneer effort and conducted through surveying various wetlands including ponds, lakes, streams, rivers, waterfalls, roadside seeps, etc. across the Darjeeling Himalayan and Jalpaiguri sub-Himalayan regions of West Bengal.The survey methods consisted of repeated collection of mainly adults at 86 different sampling sites from March 2011 to October 2013 as adults are required to make species-level determinations in most cases. In order to investigate faunal diversity from a wide array of habitats of the study area, collections were carried out at headwaters of different rivers as well as at various points downstream.
The survey focusing on species identification and documentation resulted in a total of 2003 examples belonging to 61 species under 34 genera and 14 families of which15 species are new records to the State of Bengal and one species of Enithares unicata Lundblad is a new report to India. Bal & Basu (1994) reported a total of 22 species from both Darjeeling and Jalpaiguri Districts. The current study further adds a total of 40 different species to the checklist of Darjeeling and Jalpaiguri region. Further, the present study also addressed the diagnosis of common and existing species with detail photographs and genitalic structures, which are not discussed earlier and a special approach was to prepare a key for identifying the family, genera, and species of aquatic and semi-aquatic Hemiptera of Darjeeling and Jalpaiguri region of West Bengal. During the survey, 11 species were already described new to science and published in reputed journals, which indicates that the Himalayan and sub-Himalayan regions of West Bengal harbour rich diversity of aquatic and semi-aquatic Heteroptera. Though, due to inaccessibility to many regions and climatic harshness of this region, many areas remain unexplored. Two families, Ochteridae

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and Gelastocoridae were not encountered during the present study as they are cryptic in nature and hence might have been overlooked during the survey. The present study highlights that genera like Velia, Amemboa, Micronecta, Heleocoris, Aphelocheirus, Ventidius, Metrocoris, Sigara, Tiphotrephes, etc. are poorly documented within West Bengal, and more extensive field surveys are required to understand the distribution and diversity of this group. It is also expected that other Eastern Himalayan states of India, including the northern parts of West Bengal, may also harbour more new species or new genus, which might have easily gone undetected in this underexplored region because of their cryptic habits. The majority of threats to freshwater biodiversity are linked to human population growth and development and also the increasing demand for natural resources. The Darjeeling Himalaya and Jalpaiguri Sub-Himalaya are famous for tourism being its major source of revenue. The area is under severe pressure due to rapid urbanization as a consequence of growing tourism business and these emerging threats have made this area ecologically fragile. Many macroinvertebrate fauna including aquatic and semi-aquatic Heteroptera are increasingly at risk due to anthropogenic threats imposed in the streams and all other water bodies in Eastern Himalayan region. The contribution to the knowledge on water bugs to the structure and function of freshwater ecosystems has emphasized the need for the study of the local, regional, and global diversity profiles and also to formulate relevant conservation strategies for these bugs. The observed and estimated species richness in the current study clearly shows that the sampling was adequate to address diversity of water bugs in the study area.
The current research also highlighted the gap areas and the areas with rich biodiversity by using GIS applications. Mapping of species is important for management of biodiversity, species protection, and prediction of possible impacts of landuse or climate changes, which require detailed information on the distribution of organisms and the relationship between organisms and environmental variables. Once spatial distribution is mapped, the distribution and abundance can be monitored efficiently with respect to time and future changes as opinioned by Qamar et al. (2011).The fundamental need is for extensive and good quality field surveys over the study area. These surveys, however, have serious constraints such as lack of fundings for carrying out fieldwork, need of experts in taxonomy, and regulations set by the existing legislation in some parts, especially in the protected areas of West Bengal.