Teretamon spelaeum Absar, Mitra and Kharkongor, 2017 : holotype ♂, India , Meghalaya, East Jaintia Hills district, Krem Khung Cave, Larket village (25.389°N, 92.580°E), altitude 871 m ASL, 29-iii-2017, coll. P.F. Absar ( ZSINERCIV /CRU/312);

Mitra, Santanu & Pati, Sameer Kumar, 2021, A new species of freshwater crab, Teretamon kapota sp. nov. (Decapoda: Brachyura: Potamidae) and a new record from Arunachal Pradesh, North-Eastern India, Records of the Zoological Survey of India 121 (1), pp. 1-9 : 2-6

Teretamon spelaeum Absar, Mitra and Kharkongor, 2017: holotype ♂, India, Meghalaya, East Jaintia Hills district, Krem Khung Cave, Larket village (25.389°N, 92.580°E), altitude 871 m ASL, 29-iii-2017, coll. P.F. Absar ( ZSINERCIV /CRU/312); paratype ♀ (19.40 × 15.00 mm), same collection data as holotype (ZSI-NERC IV/CRU/313) .

Diagnosis: Carapace transversely ovate (CW/CL =

1.3–1.4), dorsal surface strongly convex in frontal view, glabrous, pitted; epigastric cristae visible as 2 low, broad protuberances; postorbital cristae visible, rugose; external orbital angle indistinct, low; epibranchial tooth only slightly visible; cervical grooves narrow, very shallow; eyes relatively small as compared to orbital space, with cylindrical eyestalk and relatively large cornea; chelipeds with relatively broad subdistal spine on carpus; male telson relatively narrow, proximal width ca. 1.1 times medial length, with gently concave lateral margins; G1 with acute and upcurved tip; terminal segment distinctly curved, short, ca. 0.5 times length of subterminal segment, distal part distinctly narrow, proximal part constricted, with overall structure resembling head of pigeon due to presence of very high, strongly convex, semicircular dorsal flap; vulvae on S6 closely located, transversely ovate, very large, touching and pushing suture S5/S6 anteriorly.

Description of male (Holotype): Carapace transversely ovate, distinctly broader long (CW/CL = 1.4), deep ( CH / CW = 0.5), glabrous, smooth except for few oblique striae on branchial regions; dorsal surface strongly convex in frontal view, glabrous, pitted; anterolateral margins convex, with very low granules, distinctly shorter than posterolateral margins; posterolateral margins long, medially gently concave, distinctly convergent, joining straight posterior margin; front sloping downwards, with sinuous, broad frontal margin (FW/CW = 0.3); epigastric cristae visible as 2 low, broad, rugose, protuberances, located slightly anterior to postorbital cristae; postorbital cristae visible, rugose; external orbital angle indistinct, low; epibranchial tooth only slightly visible; postorbital region shallow; mesogastric groove deep, long, bifurcated posteriorly; cervical grooves narrow, very shallow; H-shaped groove distinct; branchial regions gently inflated; frontal median triangle incomplete; epistome posterior margin with well-developed, broadly triangular medial lobe, outer parts gently sloping downwards ( Figures 2A, B ).Orbits narrow as compared to carapace size, longitudinally broad, subovate; supraorbital margin smooth; suborbital margin strongly concave, joining with supraorbital margin ( Figures 2A, B ). Eyes relatively small as compared to orbital space with cylindrical eyestalk and moderately large cornea ( Figures 2B ).

Antennules long, folded in longitudinally broad fossae; antennae very short, reaching slightly beyond base of eye stalk ( Figures 1B ). Mandibular palp 3-segmented; terminal segment simple, undivided. Third maxillipeds cover most of buccal cavity when closed; ischium rhomboidal, ca. 1.5 times as long as broad, with narrow, deep, oblique medial groove; merus subrectangular, slightly broader than long; exopod longer than ischium, reaching proximal half length of merus, with long flagellum, subequal to merus width ( Figures 2B, C ).

Chelipeds unequal, right chela larger ( Figures 2A, C ). Major chela with 2 or 3 large teeth on each finger, remaining teeth small, conical, distinct gape when fingers closed; dactylus gently curved, slender, longer than upper margin of palm; palm longer than high, with rugose outer surface; carpus rugose, with relatively broad, blunt subdistal spine; merus lacking subterminal spine ( Figures 2A, C , 3A ).

Ambulatory legs slender, long, P3 longest, slight shorter than major cheliped, P5 shortest, subequal to carapace width, generally glabrous; merus (P2–P5) elongated; propodus (P3) ca. 2.8 times long as broad; dactylus (P2–P5) gently recurved, slightly longer than propodus, with fine setae and sharp chitinous spines on margins ( Figures 2A, C ).

Thoracic sternites smooth, pitted; suture S2/S3 distinct as narrow groove, reaching lateral margins; suture S3/S4 only visible as2 short, shallow lateral grooves; sutures S4/ S5,S5/S6, S6/S7 narrow, shallow, medially interrupted; suture between S7/S8 shallow, narrow, interrupted by longitudinal medial groove, lacking transverse ridge ( Figures 2C , 3B ). Pleonal locking mechanism with prominent tubercle on submedial part of S5 ( Figures 3B ). Sternopleonal cavity deep, long, reaching to imaginary line joining bases of third maxillipeds ( Figures 2C ).

Pleon smooth, narrowly triangular, with gently concave, setose lateral margins; pleonal somite 1 shortest, narrowest; pleonal somites 2–5 progressively longer; pleonal somite 6 trapezoidal, relatively broad (medial length nearly two thirds of proximal width), distinctly longer than preceding somites, equal in length to telson, with straight, strongly converging lateral margins ( Figures 2C , 3C ). Telson triangular, narrow, proximal width ca. 1.1 times medial length narrow, with gently concave lateral margins and rounded apex ( Figures 2C , 3C ).

G1 strongly sinuous, moderately stout, with acute and upcurved tip, reaching beyond pleonal locking tubercle in situ; terminal segment medially curved outwards at angle of 45°, slender, short, ca. 0.5 times length of subterminal segment, distal part distinctly narrow, proximal part constricted, with overall structure resembling head of pigeon due to medially located, very high, strongly convex, semicircular dorsal flap; groove for G2 marginal; subterminal segment stout, strongly sinuous ( Figures 3B, D, E , 4A, B ). G2 slightly longer than G1, ca. 1.1 times G1 length; distal segmentextremely long, ca. 0.7 times length of basal segment; basal segment moderately stout at proximal third ( Figures 3F , 4C ).

Colour in life: The crab has a reddish-brown colouration ( Figure 1 ) except for the dark brown pleon.

Paratype: The male paratype (ZSI-WRC C.1981) is a subadult male, but resembles the holotype in most of the carapace features and gonopod structure, including the diagnostic characters ( Figures 5A–E ).

Female: The examined female specimens include a juvenile, a subadult, and an adult crab. The adult female (ZSI-WRC C.1906) possesses most of the non-sexual character states as in the males. Its pleon is ovate in outline and covers the thoracic sternum except for S1–S3, lateral edges when closed ( Figure 6A ). The pleonal somite 1 is the shortest; the pleonal somites 2–5 are progressively longer; and the pleonal somite 6 is the longest, much broader than long, slightly shorter the telson, with the gently convex lateral margins ( Figure 6A ). The telson of the adult female is broadly ovate, broader than long, with gently convex lateral margins and round apex ( Figure 6A ). The vulvae on S6 of the adult female are very closely located (VD/SW = ca. 0.1), open laterally, transversely

ovate, very large, occupying ca. 0.8 times the length of S6, deep, touching and pushing suture S5/S6 anteriorly, and partially covered by a soft operculum ( Figure 6B ).

Etymology: The species epithet used here as a Latin noun in apposition, ‘kapota’, the name in Sanskrit for pigeon. The terminal segment of the male first gonopod of species most resembles a pigeon’s head.

Habitat: The holotype specimen was collected from a shallow hill stream following through a secondary forest ( Figure 7 ). The hill stream joins with the Sibyia River. The crab was found under a large boulder in the stream bed. Two other potamid crabs viz., Acanthopotamon fungosum ( Alcock, 1909) and A. horai Pati, Mitra and Yeo, 2019 also dwell in the same stream bed.

Geographic distribution: Teretamon kapota sp. nov. is currently known from the East Siang and Lower Dibang Valley districts of Arunachal Pradesh state in the north-eastern India.

New State Record

Figures

Figure 1. Teretamon kapota sp. nov., holotype male (26.50 × 18.42 mm) (ZSIK C.8541/2): colouration of freshly preserved specimen.

Figure 2. Teretamon kapota sp. nov., holotype male (26.50 × 18.42 mm) (ZSIK C.8541/2): A. Overall dorsal view; B. Frontal view of cephalothorax;C. Overall ventral view.

Figure 3. Teretamon kapota sp. nov., holotype male (26.50 × 18.42 mm) (ZSIK C.8541/2): A. Outer view of right or major chela; B. Right G1 terminal segment in situ; C. Pleon and telson; D. Dorsal view of left G1; E. Ventral view of left G1; F. Left G2.

Figure 4. Teretamon kapota sp. nov., holotype male (26.50 × 18.42 mm) (ZSIK C.8541/2): A. Dorsal view of left G1; B. Ventral view of left G1; C. Left G2.

Figure 5. Teretamon kapota sp. nov., paratype male (15.88 × 11.83 mm) (ZSI-WRC C.1981): A. Overall dorsal view; B. Frontal view of cephalothorax; C. Overall ventral view; D. Dorsal view of left G1; E. Left G2. Scale bars = 10 mm (A–C), 1 mm (D, E).

Figure 6. Teretamon kapota sp. nov., female (23.13 × 16.83 mm) (ZSI-WRC C.1906): A. Pleonal somites 4–6 and telson; B. Thoracic sternites showing vulvae. Scale bar = 2 mm.

Figure 7. View of the type locality of Teretamon kapota sp. nov.