Clypeocaenis malzacheri Srinivasan, Sivaruban, Barathy & Isack 2022, sp. nov.

Clypeocaenis malzacheri Srinivasan, Sivaruban, Barathy & Isack sp. nov.

(Figs. 1–8)

Materials Examined. Holotype (in ethanol): Male larva (Reg. No. ZSI–SRC/I/E/599), South India, Tamil Nadu, Theni district, Kurangani, Kottakudi River, 10°08′09″N, 77°25′52″E; 632 m; 28.x.2020, Pandiarajan Srinivasan & Rajasekaran Isack. Paratypes (also in ethanol): 1 male larva (Reg. No. ZSI–SRC/I/E/600), 2 male larvae (AMC / ZN/192), 4 female larvae (AMC /ZN/193), same data as holotype.

Descriptions.

Final larval instar. Body length (without cerci): 2.5–2.7 mm (male) and 2.9–3.1 mm (female); cerci lengths about 1.15 mm; antennae lengths 0.81–0.85 mm. General body coloration usually dark brown dorsally and pale yellow ventrally, though sometimes lighter dorsally. Head: General color brownish, with vertex darker with branch-like pigmentation (Fig. 1); epicranial sutures dark. Compound eyes black, ocelli whitish. Scape and pedicel chagrined without any setae; pedicel length 1.6 times length of scape. Frons distinctly protruded to proximal margin of second flagellum segment (Fig. 2A), with two simple setae on anterior margin with lengths about ¼ length of antenna. Labrum (Fig. 2B) 2.3 times as broad as long; emargination without any setae; anterior margin with row of long and thin setae; dorsum with few, long and thin setae near anterior margin and lateral margin. Mandibles (Fig. 2C) with three denticles on outer incisor and two transversely arranged denticles on kinetodontium; basal area below mola chagrined and with no setae; two transverse row of simple setae on the dorso-lateral surface in which apical row bears 4 simple setae and basal row with numerous long, simple setae; basal half of mandible chagrined. Maxilla (Fig. 2D) with two-segmented palp with protuberance; segment II 3.1 times longer than segment I; distal 3/4 of segment II covered with long, thin setae; outer margin of segment I with row of 8 stout setae (n=4) and inner margin bare. Galea-lacinia with row of 5 long, thin setae in the inner margin. Apical margin of superlingua covered with long, simple setae; hypopharynx with very short spines at apical margin. Labium (Fig. 2E): glossae ovate with apical margins covered with thin setae; paraglossae bent towards glossae and bluntly pointed, covered with thin setae; palps three-segmented, with segment III longer than segments I and II, segment III with bluntly pointed tip (Fig. 2F), segment III with two transverse rows of five stout setae at distal margin, segment II with two bipinnate bristles at distal margin (Fig. 2G), and segment I with seven unipinnate bristles on outer margin (Fig. 2H). Thorax: Pronotum dark brownish, margins light brownish. Anterolateral areas of pronotum produced. Mesonotum dark brownish. Legs: Evenly covered with scales, coloration pale to medium brown; ovoidal cuticular blank located on the proximal half of ventral surface of each femur of all legs (Fig. 4A). Foreleg (Fig. 3A): lengths of femur/ tibia/ tarsus/ claw viz., 0.50/ 0.47/ 0.49/ 0.15 mm. Coxa denticulate with thin setae on inner and outer margins. Femur (Fig. 4B) with scattered spine-like setae along inner margin; outer margin with long, simple setae present on part of proximal half and row of spatulate setae present on part of distal half; dorsal surface with 3 or 4 stout setae (Fig. 4B & 4C). Tibia with two transverse rows of very long filtering setae on dorsal side, prolonged on ventral side in longitudinal direction (Fig. 4B). Tarsus with loose row of 6 long, simple setae extending nearly longitudinally; outer margin with scattered hair-like setae; 8–10 long, bipinnate setae on inner margin. Claw long and slender, with 4 denticles varying in size, basal denticle very small compared to others (Fig. 4D). Midleg (Fig. 3B): lengths of femur/ tibia/ tarsus/ claw viz., 0.53/ 0.35/ 0.31/ 0.13 mm. Coxa similar to foreleg. Femur (Fig. 5A) with rows of spatulate setae on outer and inner margins and two feathery setae near surface of distal half of outer margin. Tibia (Fig. 5B) inner margin with row of spines on the distal half and one large, monopectinate seta present; outer margin with scattered hair-like setae. Tarsus (Fig. 5B) inner margins with row of spine-like setae; outer margins with scattered hair-like setae; 4 bipinnate bristles present medially (Fig. 5C). Claw long and hooked with 3 denticles increasing in size distally (Fig. 5D). Hindleg (Fig. 3C): lengths of femur/ tibia/ tarsus/ claw viz., 0.73/ 0.48/ 0.38/ 0.17 mm. Coxa similar to foreleg. Femur (Fig. 5E) with row of feathered setae on outer margin and row of broadly spatulate and pinnate bristles on inner margin (Fig. 5F); outer margin with 2 simple setae in distal half (Fig. 5G). Tibia with row of spatulate setae on outer margin and row of simple setae with broad apices on inner margin. Tarsus and claw similar to midleg. A bdomen: Terga I, VIII, and IX brown; others whitish and laterally translucent. Tergum II (Fig. 6A) with upright, backwardly curved blunt medial projection; posterior margin with pointed spines; surface with scales. Terga VII and VIII with medial protuberances (Fig. 6C); posterior margin of tergum VII (Fig. 6C) with short, bifid setae medially and pinnate setae laterally; terga VIII –X with denticles on posterior margins. Sterna VII – IX light brown; others whitish; hind margin of sternum IX slightly concave and denticulate (Fig. 6B). Tergalii: tergalius I bluntly pointed, two-segmented; segment II three times as long as segment I. Tergalius II quadrate (Fig. 6D, 7A), pale brown, evenly covered with scales (Fig. 6D); posterior margin with stout, multi-branched bristles; inner margin with row of small, simple setae; outer margin with stout, multi-branched bristles. Tergalii III– VI subtriangular (Fig. 7B), fringed with some bifid fimbriae. Tergalii III– VI with 45–50 filaments (only 13 filaments with 2 branches, all other filaments simple). Cerci translucent.

Egg. Length: 115–120 μm; width: 60–65 μm. Elongate, about twice as long as wide (Fig. 8A); chorion smooth without any epithema (Fig. 8B); micropyle of moderate length; mouth not broadened with circular sperm-guide (Fig. 8C).

Imago. Unknown.

Larval Diagnosis. The new species has a unique combination of features: (i) frons strongly protruding up to the proximal margin of the second flagellum segment (Fig. 2A); ii) ovoidal cuticular blank located on the proximal half of ventral surface of each femur of all legs (Fig. 4A); iii) forefemora lack long setae in the middle of the inner margin (Fig. 4B); iv) claws with 4 denticles in the foreleg varying in size, basal denticle very small compared to others and, 3 denticles increasing in size distally in the mid and hindleg (Fig. 4D & 5D); v) abdominal tergum II with upright, backwardly curved blunt medial projection (Fig. 6A); and vi) hind margin of abdominal sternum IX slightly concave and denticulate (Fig. 6B).

Etymology. This species is named after Dr. Peter Malzacher (Ludwigsburg, Germany), in honor of his dedication to caenid mayflies. The epithet “malzacheri” is used as a nomen in the genitive case.

Distribution. Kurangani hills, Tamil Nadu, India.

Biology. The larvae of Clypeocaenis malzacheri sp. nov. show a significant level of languor in their activity. They live on cobble and pebbles in areas with slow current. They were found in water with temperature ranging between 21°C–23°C and pH ranging between 7.1–7.3.