Taxonomical Keys for Morphological Identification of Coral-Associated Polychaetes from Great Nicobar Islands

The present study illustrates the insufficient taxonomy records and highlights the better knowledge of microscopic diagnostic tool in polychaete taxonomy. It leads to better understanding of coral-associated polychaete taxonomy in Great Nicobar Islands, India. Total 24 species under 14 genera, 7 orders, and 11 families were identified for the identification key purpose, in spite of 3 species of Phyllocidae, 8 species of Nereidae, 5 species of Eunicidae, 2 species of Spionidae, and 1 species of Opheliidae, Sabellariidae, Terebellidae, Polynoidae, Amphinomidae, and Sabellidae. The current status of taxonomic information varies greatly among taxa and among geographic areas within taxa. Problems include nomenclature, diagnoses, and determination of taxonomic relationships. We provide examples of a variety of these problems. Each species has distinct features of the particular families, and taxonomic section of this chapter to assists the polychaete identification is necessary to assess the biodiversity and taxonomy of at any levels. This chapter considers the importance of monitoring biological diversity, current morphological taxonomy of polychaetes and describes the approach developed for protected areas in Great Nicobar Islands.


Introduction
Generally, the taxonomy is essential for basic identification keys for animal kingdom to learn about the global biodiversity, in a better way, and gain the knowledge and understanding of bio-resources and its wise use. Correct identification of the organisms is necessary to analyze and assess the biological diversity of an ecosystem at all levels, namely, diversity among ecosystems, phyletic diversity or diversity of species, and their genetic diversity among species receiving increasing attention [1,2]. Polychaetes are a large group of segmented worms that display a wide range of morphological diversity [3]. Identifying organisms precisely at species level is fundamental to any ecological research and environmental monitoring. Generally, identification of polychaetes at species rank is quite difficult without illustrated monographs which may have been hampered by their morphological similarity to their fully marine counterparts [4]. Polychaetes vary widely from generalized pattern and can display a range of different body forms. The most generalized polychaetes are those that crawl along the bottom, but others have adapted many different ecological niches including burrowing, pelagic life, tube dwelling or boring, and commensalism and parasitism, requiring various modifications to their body structure.
In polychaete taxonomy, parapodia are the important organ for identification particularly segment of origin, shape, and structural composition in body regions. Special features of branchiae or occurrences of multiple cirri are also important.
A key morphological feature of seta construction, notopodia for the superfamilial and ordinal levels, and development of each ramus with the various parapodial lobes and cirri are very important at the generic and species levels. The presence of branchiae may not even be considered a specific character [5]. A number of pioneering conventional taxonomic studies on polychaetes were made by Fauvel [6,7], Day [8] and Fauchald [9]. There is yet a lag in making taxonomic information available in many ecological programs and databases for polychaetes. In early studies, all the characteristics were mainly featured by diagrammatic figures. The importance of accurate examination of the setae is still underestimated by most taxonomists; the precise observations must require close microscopic analysis to make proper identification, which should be followed for all taxonomic studies as a routine [9]. Thus, the present study was focused to analyze the taxonomical features of Great Nicobar Island polychaetes through advance magnification techniques to improve the quality and precision of identification through key characteristic features.

Study area
Great Nicobar Islands, the southernmost land piece of India, has the greatest length of about 55 km between North Murray Point and South Indira Point. It has a width of about 30 km in the north but narrows down to about 3 km at the southern tip (Figure 1). In the present study, samples were collected from 11 different stations in the intertidal region of the Great Nicobar Islands (Tables 1 and 2).

Sample collection
Samples collected from the intertidal areas, the dead coral material were broken down in to smaller fragments with the help of hammer and chisel. Polychaetes picked with the help of forceps were transferred to plastic containers, before fixation, into strong alcohol to have their pharynx everted, which will aide in the identification of the group. Samples were fixed with 10% formalin diluted with seawater and were later transferred to 70% ethanol the purpose of staining, Rose Bengal stain was used.

Examination of specimens
Stained specimens were placed in petri dish containing tap water to dissect the morphological features of parapodia and proboscis of the jaws and other features of all the family which were made into thin sections with a surgical blade (No. 2) and were mounted on slides to examine under a compound binocular microscope (Olympus CX41). Specimens were sorted up to genus level, and later detailed examination staining of specimens with Rose Bengal provided a useful diagnostic tool. The diagnostic tool in some families had good refractive qualities even at high magnification, and thickness of the mount was easily controlled. A thicker mount was necessary when viewing larger structures such as parapodia, cross sections, and the whole animal as such. The specimen was mounted in lactophenol and then heated carefully to avoid air bubbling. This procedure clears the tissue immediately making chitinized internal structures such as jaws and acicula more visible. Compound microscope was used to elucidate the small structures of setae and the permanent mounts of the parapodia and setae with polyvinyl lactophenol. All the characteristic features of the polychaetes focused in the light microscope and labeled image were done by correct pathway. All the species were identified with the help of the standard illustrated manuals of Fauvel [7] and Day [8].

Results
At all stations, polychaetes were found to be the dominant group with 24 species belonging to 2 major classes, 14 genera, and 7 orders with 11 different families selected for the morphological studies. Among these Polynoidae, Amphinomidae, Sabellariidae, Terebellidae, Sabellidae, and Opheliidae accounted for 1 species in their group, and the rest comprised of 3 Phyllocidae, 8 Nereidae, 5 Eunicidae, and 2 Spionidae. Each species has distinct features, and the taxonomic section serves as a key to genera, generic diagnoses, and species identification with their physiological characteristics. Each species description comprised several sections.

22.
Idanthyrsus pennatus (Peters, 1985) Hard tube formed with sand particles on corals and rocks  Habitat: Living in crevices of rocks and dead corals. Description: Body elongated, 10-15 mm wide, and dorsoventrally flattened; prostomium with pair of eyes having three antennae (Figure 2a). One pair of palps is color pale red with light brown branchiae and white setae. The caruncle terminates on the anterior part of the fourth setiger. Its lateral lobes are not very clear since they are hidden. Gills begin on the second setiger and extend to the end of the body (Figure 2b). The notosetae vary greatly and are long and white with a slender, elongated tip and a few serrations along the cutting edge together with a spur below the serrations; large, straight, and harpoon-shaped setae with recurved fangs (Figure 2d). The neurosetae are short forked with unequal prongs (Figure 2c), and slender setae have a small spur (Figure 2e) (Figure 3a). Prostomium is square deeply bilobed with two tentacles and four eyes (Figure 3b). Habitat: Crevices of dead corals and beach rocks of intertidal zone. Description: Body elongated, 400-460 mm long with numerous segments. Each segment is slender and yellowish with a dark crossbar on. Prostomium is oval or square with an occipital papilla in the posterior notch (Fig. 4a). Antennae are ovoid dorsally; first tentacular segments are not visible, but the second and third are distinct and separate. Tentacular cirri are cylindrical; others are tapered having long cirrophores and short swollen cirrostyles. Tentacular segments without setae. Dorsal cirri are reddish, oval, broader, and long (Figure 4b). Setigerous lobes are long and faintly bilobed. Ventral cirri are oval and uniramous, and parapodia have compound seta spinigers (Figure 4c and d).
Remarks: The present material agrees well with the descriptions of Day [8]. Habitat: Crevices of dead corals and beach rocks in intertidal zone. Description: Body long, slender with numerous segments. Prostomium is heart shaped with a pair of prominent black eyes (Figure 5a). Posterior margin of prostomium is notched and a small occipital tentacle is present. Four short subulate tentacles. The longest tentacular cirri reach back to the seventh setiger. Numerous irregular rows of short papillae at the base of the long proboscis. Feet are uniramous (Figure 5b). Dorsal and ventral cirri are foliaceous, lanceolate, nearly twice as long, and broad. Ventral cirri are small and broad (Figure 5c). Compound setae are minutely serrated (Figure 5d).
Remarks: The present material agrees well with the descriptions of Day [8].  fig. 5.3d-f. Habitat: Crevices of dead corals and beach rocks of intertidal zone. Description: Body is short with some red pigmentation; prostomium is bluntly triangular with four antennae (Figure 6a); no occipital tentacles. Tentacular segments are separated from the prostomium, but the first is often fused to the second, and only the third is separated dorsally and distinct. Proboscis is slender with covered small irregular arranged papillae. All tentacular cirri are short and spindle  shaped. The second and third tentacular segments with setae. Dorsal cirri are cordate and reddish, and setigerous lobes are bluntly rounded apically (Figure 6b). Ventral cirri are oval. Setae are few, with long shafts ending in truncate and strongly striated shaft heads. Blades are short and dagger-like (Figure 6c).
Remarks: In earlier description this species is the first record in Andaman and Nicobar waters.
Distribution: Australia, Japan, New Zealand, Ceylon, Read Sea, California, Tuticorin pearl bank, and India.
Ceratonereis mirabilis (Kinberg,  Habitat: Silty sand substratum under coral rubbles and surface of dead corals. Description: The prostomium is broad, more than twice as wide as long and has a deep cleft between the antennae. The basalia of palps is quite long, and terminalia is button shaped (Figure 7a). Two pairs of eyes in rectangular arrangement. The longest peristomialcirus extends back to the 17th setiger. Prostomium and dorsum of palps are light green, and dorsum of segment has distinct light green or greenbrown band, which becomes lighter toward posterior. The other parts of the body are white. Paragnaths are present only on maxillary ring of the proboscis: I = 0; II = 10-13 cones in 2 oblique clusters; III = 7-9 cones in 1 cluster; and IV = 10-14 cones.    Lateral teeth of the jaw are indistinct (Figure 7e). The first two pairs of parapodia are uniramous, the rest biramous. The dorsal cirrus is very long, three times as long as notoligule. Neuroligule is slightly shorter but thicker (Figure 7b and c). The dorsal and ventral cirri are digitate; acicular lobes are very small, only as a projection, shorter than ventral cirrus. The dorsal cirrus of anterior parapodia is five times long as notoligule, and notoligules digitate, while supra-notoligules are thicker.
The acicular lobes of neuropodium are short and distally obtuse; neuroligule is short but slightly longer than neuro-acicular lobe. The dorsal segments of middle and posterior cirrus are rather long. Anterior notoseate are homogomph spinigers. Indistinct heterogomph falcigers appear from the middle parapodium, and the end of terminal piece is beaked. Some posterior setigers bear homogomph falcigers in which the end of terminal piece is bifid. Notopodial falcigers are homogomph; neuropodial falcigers are homogomph (Figure 7d).
Remarks: The species is characterized by its cleft prostomium and the presence of notopodial falcigers on posterior setigers. Habitat: Found among oysters and dead coral crevices of low tide. Description: Body 50-60 mm long with three rows of brown marks, and prostomium is "V"-shape trapezoidal with deep median furrow anteriorly; tentacular cirri are short. Palps with robust, short palpophores, and globular palpostyles. Antennae two short, triangular longest tentacular cirri usually extend to third setiger. Peristomium is relatively long (Figure 8a). Anterior notopodia, subtriangular; notopodial ligules, conical; median ligules with small superior lobes (Figure 8b). Dorsal cirrus is as long as dorsal notopodial lobes on anterior setigers and slightly longer posteriorly (Figure 8c). Neuropodia with digit firm superior lobe; low, rounded inferior lobe; shorter post-setal lobe with straight border.
Remarks: The present materials agree well with the earlier descriptions. Description: Maximum length of specimen is 100 mm long and 6 mm wide. Prostomium is pyriform, with pairs of eyes in trapezoidal arrangement situated on the posterior part of prostomium (Figure 9a). Tentacles are short and small and distally slender; the palps are large, and the basalia is expanded; the terminalia is   very small and button shaped. The longest peristomial cirrus extends back to the seventh setiger.
Typical parapodia have all ligules conical with the dorsal longest ones (Figure 9b). Dorsal cirri are slender and extend distally somewhat beyond the tips of dorsal ligules (Figure 9c). The anterior setigers, more than 10 in a live specimen, are blue-black or green-black; the posterior region is pale-brown. Notosetae with homogomph spinigers and neurosetae with heterogomph falcigers (Figure 9d).
Remarks: The present materials agree well with the description of Fauvel [7]. Description: Body 120-125 mm long, eyes black in color. A prominent, circular depression present in anterior prostomium between the antennae. Antennae are one third long as prostomium. Tentacular cirri extend back to 2-4 setigers (Figure 10a   cones on each side close to area VI. Parapodia of first and second setigers are anteriorly directed. Anterior notopodia with two equal lobes (Figure 10c) and basal lobe becoming expanded from median setigers up to twice as long as ventral lobe with distally attached dorsal cirri. All notosetae are homogomph spinigers. Neurosetae are heterogomph spinigers and heterogomph falcigers in both supra-acicular and infraacicular positions. Neuropodial heterogomph spinigers are absent from anterior-most 24th-35th setigers. Anal cirri are as long as posterior-most fourth setigers (Figure 10d).
Remarks: The present material agrees well with the description of Wilson and Glasby [36]. In earlier collections as a new distribution record species in Andaman and Nicobar Islands [37].
Distribution: Australia and Philippines.
Anterior parapodia bear rounded supra-and infra-ligules (Figure 14b). Both dorsal and ventral cirri are digitate, and middle parapodia have almost the same size as notoligule; but the end of the supra-notoligule is slender. The dorsal cirri are longer than notopodial lobes slenderized toward the end. The ventral cirrus is very short, situated at the base of infra-neuroligule (Figure 14c). Beyond the 50th setiger, supra-notoligule expands toward the posterior end in rectangular shape; it is carrying the dorsal cirrus at the end; ventral cirrus is very short. The upper margin or supra-notoligule in posterior parapodia bears a gland. Notosetae are homogomph spinigers throughout, and neurosetae in anterior and middle parapodia are homogomph spinigers and heterogomph falcigers. Posterior neurosetal lobes with heterogomph spinigers and falcigers (Figure 14d).
Remarks: The present material agrees well with the description of Day [8]. Habitat: Boring into dead corals and beach rocks. Description: Body 30-155 mm long, prostomium is bilobed with five prostomial tentacles, pair of tentacular cirri on the second apodous segment, and the dorsal cirri and anal cirri are moniliform. The first apodous segment is about three and a half times as long as the second apodous segment (Figure 15a). The setae of the first foot are arranged in two bundles. A bundle of simple capillaries at the base of the dorsal cirrus (Figure 15b). Branchiae first start on the 6th setigerous segment well developed between the 10th and 25th segments, where they have 6th or 7th filaments, and decrease to two or three in median region; thereafter, the number increases again in posterior segments (Figure 15c). The anal segment bears two long anal cirri. Acicular setae are first present in the 19th setigerous segment; they are yellow, tridentate, and distally hooded. Other setae include slender capillary, bidentate compound falcigers with rounded hood, and pectinate setae with lateral, asymmetrical extensions (Figure 15d) fig. 158 h-n; [8]: 385, fig. 17.3a-e. Habitat: Boring into dead corals and living on cavity of dead corals and rocks. Description: Body 30-35 mm long, anterior segments with red bars which fade in alcohol, antennae and cirri are smooth without annulations, the longest or median one extends back to the sixth segment (Figure 16a). A pair of circular eyes at the outer bases of the median antenna, tentacular cirri are smooth and extend forward not quite to the front of the prostomium. Branchiae are first present from the third parapodium (Figure 16b and c) and continue back to 45th segment; they have 10-18 filaments. Acicula is yellow with blunt tips, slightly curved. Acicular setae are yellow and tridentate with small apical tooth. Compound setae are falcigerous and are distally bifid and covered with a pointed hood (Figure 16d).
Remarks: In earlier findings of Rajasekaran [37], this species is the first record from Indian waters. Habitat: Boring into beach rocks and dead corals. Description: Body 130-140 mm long, brown in color with dotted tiny white punctations on the anterior portion. Prostomial antennae are smooth, and peristomial cirri are long as the peristomial segment (Figure 17a). From the first segment, branchiae are absent (Figure 17b) Branchiae are starting from about 16th segment, with 2-4 filaments; they are pectinately divided and attain a maximum of 8 filaments at the 30th setiger; the last 10 segments lack them (Figure 17c). There are 2 acicula each of the first 28-30 parapodia and only 1 in others. Acicular hooks are first present in 30th segment; they are distally bidentate and subdistal tooth is directed laterally. Other setae are of three kinds: slender capillary (Figure 17d), pectinate (Figure 17f), and bidentate compound falcigers in which the hood is distally rounded (Figure 17e) fig. 17.8.a-f; [7]: 248, fig. 124a-g; [13]: 205; [14]: 78.
Habitat: Boring in dead corals and living on cervices of dead corals. Description: Prostomium is distinctly bilobed in front and has two reniform eyes located near the outer base of the paired antennae (Figure 18a). The three prostomial antennae are slender, and the second dental plate has three heavy teeth. In anterior segments the dorsal cirri are slenderer than ventral ones (Figure 18b  and c). In posterior segments the dorsal cirri become shorter. Setae include capillary setae (Figure 18d), bidentate composite falcigers, and comb setae, and bidentate  (Figure 19a). Prostomial antennae are short and three in number, and peristomial appendages and gills are absent. Each parapodium with bluntly conical dorsal cirrus, rounded ventral cirrus, and a broad setigerous lobe (Figure 19b). Setae include capillaries with pectinate setae, composite falcigers, and bidentate acicular hooks (Figure 19c). Acicula black with blunt tips. Bidentate sub-acicular hooks from the 22nd-25th setigers onwards.

Malacocers indicus
Remarks: In earlier findings 9 specimens are collected from station 2 and 10 and the first record of the genus is from Andaman and Nicobar Islands.   fig. 18.7c-h, [18]: 153.
Habitat: Silty sediments in sandy shore areas. Description: Body 55-60 mm long, prostomium is pointed anteriorly with 4-5 pairs of eyes in a row and a well-marked occipital keel reaching the second setiger (Figure 21a). A pair of long and stout coiled palps; branchiae start from the second setiger and continue to the posterior end and attached to the dorsal lamellae (Figure 21b). Only capillary setae are present in the first few segments (Figure 21c  and d). Bidentate hooded hooks in the neuropodia from the 30th-35th setigers onwards and in the notopodia from the 60th setiger (Figure 21e). A maximum of 12 neuropodial hooks, pygidial cushion is small, broader, and long.
Remarks: This is the first record of the genus from Andaman and Nicobar Islands [37].
Distribution: Mozambique, Madagascar, Atlantic Ocean, and Mediterranean Sea. India: Orissa coast, Rushikulya estuary, Visakhapatnam coast, Pulicat Lake, Vellar estuary, and Godavari estuary.   (Figure 22a). The gills arise from the second setiger to the last setiger. Eyes are lateral-spots on the 7th setiger to around the 18th setiger. The parapodia arise from the dorsal margin of the ventrolateral folds. Parapodia with short presetal lobe, short ventral cirrus (Figure 22b), and two bundles of capillary setae (Figure 22c). Anal funnel is long and obliquely truncate so that the anus opens upward. It has long ventral cirrus and 12 fine dorsal papillae.
Remarks: Aramandia leptocirrus is extremely specialized, being highly adapted to life within sandy sediments. The branchiae are directed backwards and are present from the anterior end of the ventral groove. Description: Body 30-60 mm long, prostomium covered by two large opercular stalks bearing modified setae in two rows, paleae of the opercular peduncle with a number of 19-32 pairs in the outer row and 15-18 pairs in the inner one (Figure 23a). Outer paleae with strongly curved shaft and slender denticles giving the general impression of a feather or a palm leaf (Figure 23c). Inner paleae smooth with tapering tips (Figure 23b). The middorsal line of the opercular peduncle has a  pair of nuchal hooks (Figure 23e) and a pair of long papillae. The second segment has a pair of branchiae. The three parathoracic segments are biramous. Thoracic uncini have eight teeth (Figure 23d). Caudal region is achaetous and apodous. Segments are numerous and indistinguishable.
Remarks: The present material agrees well with the description of Day [8]. Habitat: Soft tube forming on dead and live corals at 1 meter water depth. Description: Body 35-40 mm in length with long and coiled tentacles; tentacles are filamentous, numerous, and slender. Three pairs of arborescent gills are present on segments 2, 3, and 4 (Figure 24a). Lateral lobes are lacking. The peristomium has eye spots. Notosetae are first present from the fourth segment and continue posteriorly but are absent from the last 40 segments. Setae are very slender and distally serrated (Figure 24b). Uncini are in single rows on segments 5-10 and the last segment and in double rows on other segments. Each uncinus has 3-5 large teeth (Figure 24c).
Remarks: The present material agrees well with the original description. Distribution: Japan, China Sea, Burma, and Red Sea. India: Gulf of Mannar, Andaman and Nicobar Islands, Mahanadi River Estuary, and Gujarat.
Description: Body 35-40 mm long (Figure 25a). About 20-30 branchial radioles (Figure 25b) with the tips coiled inwards each bearing large subterminal eye. Collar is notched back dorsally to form two small and large lateral lobes, and palps are short. Thoracic notosetae of the 2nd-8th setigers include two types of setae: long slender winged capillaries (Figure 25c and d) and paleae with pointed tips (Figure 25e). Thoracic neurosetae include avicular uncini with long tails and striated crests, plus two rows of pick ax setae with symmetrical blades and tapering tips (Figure 25f).
Remarks: This is the first record of the species from Indian waters. Distribution: Red Sea, Madagascar, and Sri Lanka.

Discussion
The present study is an attempt to understand the basic polychaete taxonomical tools, diversity, and morphological identification of the common coral-reefassociated polychaetes of Great Nicobar Islands. Over 5400 species of polychaetes have been described so far worldwide. Many polychaete worms are beautiful and strikingly colored red, green, or pink or with a combination of different colors, and some are iridescent. The most common and visible polychaetes found on coral reefs are feather dust and Christmas tree worms. Hence, in the present survey, a total of 24 species belonging to 14 genera, 7 orders, and 11 families were identified for the taxonomical study purpose, in spite of 3 species Phyllocidae, 8 species Nereidae, 5 species Eunicidae, 2 species Spionidae, 1 species Opheliidae, Sabellariidae, Terebellidae, Polynoidae, Amphinomidae, and Sabellidae of coral-reef associate polychaetes are so far reported from Great Nicobar Island coastal waters. Fauvel [7]  gave about 450 species from the waters in and around India and rightly stated that this was probably half of the total number occurring in these waters. A total of 30 species of polychaetes belong to 8 families and 23 genera. Each species has specific features for the representative family, and all species were recorded for the first time from the Andaman and Nicobar Islands, of which 15 species are new to Indian waters. Prior to the study periods in Great Nicobar Islands, very less polychaete taxonomical study has been reported; the present study clearly highlights the polychaete taxonomical tools of Great Nicobar Island.

Conclusion
This chapter concludes the taxonomy status and identification tools of polychaete diversity in Great Nicobar Islands. Polychaeates are one of the best indicator species in marine environment. Coral associated polychaete identification is very difficult to identify. The study of polychaete taxonomy is a better tool for understanding the conventional taxonomy. In recent trends various molecular tools have been used for identification purpose. In spite of molecular techniques, conventional taxonomy is one of the basic important tools. Taxonomic identification is very difficult to identify in the coral-reef region could be solved by re-establishing species names at present regarded as subordinate synonyms, formerly the type or topotype resources are analyzed. Our hope is that the present list may prove useful for such a major reconsideration of this distinctive fauna and that it may encourage regional colleagues to expand our worldwide understanding of the polychaete diversity in Great Nicbar region, also this region region which may very well Islands ecosytems of the uppermost polychaete diversity in India. The results highlight the importance of the taxonomy key and evaluate the species information in around Great Nicobar Islands. In many of previous literature can used in line drawing only but the present data describe the clear illustration of digital snapshot animal parts. The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.