Abormon praecalvum, Ng, 2021

Abormon praecalvum View in CoL sp. nov.

( Figs. 1–4 View Figure 1 View Figure 2 View Figure 3 View Figure 4 )

Zoobank: urn:lsid:zoobank.org:act:4A065E0E-059B-4E3F-A9D0-941976C53F7C

Type material. Holotype: male ( CW 12.9 mm, CL 10.5 mm, CH 6.2 mm, FW 4.6 mm), Dambung Stream , approximately 1.7 km from Hawa Camp , Mouling National Park , Abor Hills, Upper Siang District, Arunachal Pradesh, India (28.686°N 94.969°E), altitude 406 m a.s.l., 28 October 2017, coll. G. Maheswaran et al. ( ZSI-WRC C.1941) GoogleMaps . Paratypes: 1 male ( CW 13.3 mm, CL 10.6 mm, CH 6.6 mm, FW 4.7 mm) , 1 female ( CW 14.5 mm, CL 11.5 mm, CH 7.1 mm, FW 5.0 mm), Ramsing Guest House , Mouling National Park , Abor Hills, Upper Siang District, Arunachal Pradesh, India (28.656°N 94.976°E), altitude 601 m a.s.l., 26 October 2017, coll. G. Maheswaran et al. ( ZSI-WRC C.1942) GoogleMaps ; 1 male ( CW 12.3 mm, CL 10.7 mm, CH 6.2 mm, FW 4.5 mm) , 1 female ( CW 14.5 mm, CL 11.6 mm, CH 7.3 mm, FW 5.0 mm), Raecel , near Ramsing , Mouling National Park , Abor Hills, Upper Siang District, Arunachal Pradesh, India (28.652°N 94.986°E), altitude 785 m a.s.l., 27 October 2017, coll. G. Maheswaran et al. ( ZSI-WRC C.1943) GoogleMaps .

Other material. 1 male ( CW 10.1 mm, CL 8.1 mm, CH 4.6 mm, FW 3.8 mm) , 3 females ( CW 12.3–14.1 mm, CL 9.8–11.3 mm, CH 6.4–6.7 mm, FW 4.4–4.6 mm), same data as ZSI-WRC C.1942 ( ZSI-WRC C.1944) GoogleMaps ; 1 male ( CW 12.7 mm, CL 10.5 mm, CH 6.3 mm, FW 4.7 mm) , 3 females ( CW 9.2–13.7 mm, CL 7.1–10.8 mm, CH 4.4–6.5 mm, FW 3.5–4.9 mm), Gamta , near Ramsing , Mouling National Park , Abor Hills, Upper Siang District, Arunachal Pradesh, India (28.655°N 94.968°E), altitude 891 m a.s.l., 26 October 2017, coll. G. Maheswaran et al. ( ZSI-WRC C.1945) GoogleMaps ; 3 males ( CW 10.0– 14.2 mm, CL 8.2–11.7 mm, CH 4.8– 6.8 mm, FW 3. 6–5.0 mm) , 5 females ( CW 10.7–14.4 mm, CL 8.7–11.4 mm, CH 5.0– 6.7 mm, FW 3.9–4.9 mm), same data as ZSI-WRC C.1943 ( ZSI-WRC C.1946) GoogleMaps ; 1 male ( CW 13.1 mm, CL 10.6 mm, CH 6.2 mm, FW 4.7 mm), Ramsing , Mouling National Park , Abor Hills, Upper Siang District, Arunachal Pradesh, India (28.663°N, 94.989°E), altitude 444 m a.s.l., 3 November 2017, coll. G. Maheswaran et al. ( ZSI-WRC C.1947) GoogleMaps .

Diagnosis. Small species (CW <15 mm). Carapace ovate, broader than long (CW/CL= 1.2–1.3), relatively high ( CH /CW = 0.5); dorsal surface sparsely setose; epistome posterior margin with triangular medial tooth, sinuous lateral margins ( Figs. 1A, B View Figure 1 , 2A View Figure 2 , 4A View Figure 4 ). Chelipeds sparsely setose, with relatively broad inner distal major tooth on carpus ( Figs. 1A–C View Figure 1 , 2C View Figure 2 , 4A View Figure 4 ). Ambulatory legs sparsely setose ( Figs. 1A–C View Figure 1 , 4A View Figure 4 ). Male pleon broad, triangular, with gently sinuous lateral margins; pleonal somite 6 trapezoidal, with straight lateral margins ( Figs. 1C View Figure 1 , 2E View Figure 2 ). G1 relatively stout, with terminal segment relatively more curved outwards at angle approximately 30° from longitudinal axis; terminal segment relatively stout and short, approximately 0.5 times combined length of f lexible zone and subterminal segment, dorsal flap low, broadly rounded, medially located; subterminal segment gently sinuous, relatively stout, broader basally, distinctly narrow distally forming gentle shelf on outer margin, lacking protuberance on inner margin at distal end ( Figs. 2D View Figure 2 , 3A–C View Figure 3 ). G2 1.1 times G1 length; distal segment long, approximately 0.5 times length of basal segment, with blunt tip; basal segment stout at proximal third ( Fig. 3D View Figure 3 ). Female telson broadly ovate, with broad apex ( Fig. 4B View Figure 4 ). Vulvae located apart from each other (VD/SW = approximately 0.2); posterior sternal vulvar cover visible as slightly raised plate ( Fig. 4C View Figure 4 ).

Description of male holotype. Carapace small (CW 12.9 mm), transversely ovate, broader than long (CW/ CL = 1.2), moderately deep ( CH /CW = 0.5); dorsal surface gently convex in frontal view, rugose, punctate, sparsely setose; anterolateral surface gently inf lated in frontal view; anterolateral margins gently convex, cristate with low granules, approximately 0.4 times length of posterolateral margins measured in straight line; posterolateral margins converging posteriorly, concave medially; front sloping downwards, almost rectangular; frontal margin concave medially, smooth, cristate, broad (FW/CW = 0.35); epigastric cristae very low, visible as 2 broad, rugose protuberances; postorbital cristae indiscernible; external orbital angle triangular, with long outer margin, approximately 2 times length of inner margin; epibranchial tooth very low, with very small cleft; postorbital region gently concave; branchial regions gently inflated; cervical grooves barely visible; mesogastric groove deep, narrow, long, bifurcated posteriorly; H-shaped groove distinct; subhepatic region rugose, sparsely setose; suborbital region generally smooth, glabrous; supraorbital margin gently concave medially, cristate with low granules; suborbital margin concave, cristate with low granules, conf luent with supraorbital margin; pterygostomial region smooth except for anteriorly located low granules; frontal medial triangle incomplete, with dorsal margin only, lateral margins indiscernible; epistome posterior margin with distinct, narrow, triangular medial tooth, sinuous lateral margins ( Figs. 1A–C View Figure 1 , 2A View Figure 2 ). Eyes occupying most of orbital space; eyestalk short, stout; cornea moderately large, pigmented ( Fig. 1B View Figure 1 ).

Antennules long, folded in transversely broad fossae; antennae very short, reaching slightly beyond base of eyestalk ( Fig. 1B View Figure 1 ). Mandibular palp 3-segmented; terminal segment simple, undivided. First, second maxillipeds each with long f lagellum on exopod. Third maxillipeds cover most of buccal cavity when closed; ischium subrectangular, longer than broad, with deep, oblique medial groove; merus subpentagonal, broader than long, sunken; exopod moderately stout, distally blunt, longer than ischium, reaching proximal third of merus, without flagellum ( Figs. 1B, C View Figure 1 , 2B View Figure 2 ).

Chelipeds rugose, sparsely setose, unequal, right chela larger ( Fig. 1A–C View Figure 1 ). Major chela with 4 or 5 large, blunt teeth on each finger, distinct gape when fingers closed; dactylus gently curved, moderately stout, longer than upper margin of palm, with 2 longitudinal, parallel rows of 4 or 5 distinct but low dorsal granules; palm slightly longer than high, outer surface with widely spaced low granules, inner surface generally smooth; carpus rugose, gently inf lated, with broad, moderately sharp, triangular inner distal major tooth and very low, blunt sub-basal tooth; merus rugose on outer surface, without subterminal spine ( Figs. 1A–C View Figure 1 , 2C View Figure 2 ).

Ambulatory legs moderately stout, short, P3 longest, sparsely setose; P2–P5 merus without subdistal spine, longest merus (P3) approximately 0.5 times CW; P5 propodus relatively stouter than P2–P4 propodus; P2–P5 dactylus gently recurved, subequal in length to propodus, with distinct, sharp chitinous spines on margins ( Fig. 1A–C View Figure 1 ).

Thoracic sternites punctate, sparsely setose; S1/ S2 completely fused; S2/S3 distinct as deep, narrow, concave groove, reaching lateral margins; S3/S4 visible as shallow, broad groove, running from edge of sternopleonal cavity to lateral margins; S4/S5, S5/S6, S6/S7 shallow, narrow, indiscernible towards sternopleonal cavity; S7/S8 shallow, narrow, medially interrupted by longitudinal groove, lacking transverse ridge ( Figs. 1C View Figure 1 , 2D View Figure 2 ). Pleonal locking mechanism with prominent tubercle on medial part of S5 ( Fig. 2D View Figure 2 ). Sternopleonal cavity deep, long, almost reaching to imaginary line joining anterior part of cheliped coxae ( Figs. 1C View Figure 1 , 2D View Figure 2 ).

Pleon broad, triangular, with gently sinuous lateral margins; pleonal somites 1, 2 almost rectangular, narrower than pleonal somite 3; pleonal somites 3–5 trapezoidal; pleonal somite6 trapezoidal, broader than long (proximal width approximately 2.2 times medial length), distinctly longer than preceding pleonal somites, distinctly shorter than telson, with straight lateral margins ( Figs. 1C View Figure 1 , 2E View Figure 2 ). Telson tongue-shaped, broader than long (proximal width approximately 1.4 times medial length), with concave lateral margins, apex broad, rounded ( Figs. 1C View Figure 1 , 2E View Figure 2 ).

G1 stout, sinuous, with terminal segment bent outwards at angle approximately 30° from longitudinal axis, tip blunt tapering, reaching beyond pleonal locking tubercle up to S4/S 5 in situ; f lexible zone large; terminal segment very stout, conical, long, approximately 0.5 times combined length of flexible zone and subterminal segment, dorsal flap distinct but low, broadly rounded, medially located, not reaching proximal end; subterminal segment gently sinuous, stout, broad at base, distinctly narrow distally forming gentle shelf on outer margin, lacking protuberance on inner margin at distal end;groove for G2 median ( Figs. 2D View Figure 2 , 3A–C View Figure 3 ). G2 slightly longer than G1, approximately 1.1 times G1 length; distal segment gently curved, cylindrical, long, approximately 0.5 times length of basal segment, with blunt tip; basal segment stout at proximal third, appearing narrowly ovate ( Fig. 3D View Figure 3 ).

Paratypes. Both the male paratypes (ZSI-WRC C.1942, 1943) of A. praecalvum sp. nov. are adults and resemble the holotype in general carapace physiognomy and gonopod structure. The female paratypes (ZSI-WRC C.1942, 1943) are adults and resemble with the males in all non-sexual character states except for their relatively wider carapace (CW/ CL = 1.3) ( Fig. 4A View Figure 4 ). The pleon of the female paratypes is narrowly ovate, which covers the thoracic sternum except for S1, S2, and lateral edges when closed ( Fig. 4B View Figure 4 ). In the female paratypes, pleonal somite 1 is the shortest; pleonal somites 2–5 are progressively longer; and pleonal somite 6 is the longest, much broader than long, slightly shorter than the telson, with the gently convex lateral margins ( Fig. 4B View Figure 4 ). The female telson is broadly ovate, much broader than long, with almost straight lateral margins and rounded apex ( Fig. 4B View Figure 4 ). The vulvae on S6 are located apart from each other (VD/SW = approximately 0.2), open anteriorly, transversely ovate, relatively small, occupying half the length of S6, anterior margin touching S5/S6, with the posterior sternal vulvar cover visible as a slightly raised plate ( Fig. 4C View Figure 4 ).

Etymology. The species name is derived from the Latin ‘ praecalvus ’ for ‘becoming bald’, referring to the presence of only a few scattered setae on the carapace and pereiopods of the crab.

Remarks. Abormon praecalvum sp. nov. can be distinguished from its only congener, A. capillosum sp.nov., by the sparsely setose carapace and pereiopods ( Figs. 1A–C View Figure 1 , 2A View Figure 2 , 4A View Figure 4 ) (vs. densely setose carapace and pereiopods; Figs. 5A–C View Figure 5 , 6A View Figure 6 , 8A, B View Figure 8 , 9A View Figure 9 ); the relatively broader inner distal major tooth on the carpus of the cheliped ( Fig. 2C View Figure 2 ) (vs. relatively narrower inner distal major tooth on the carpus of the cheliped; Fig. 6C View Figure 6 ); and the straight lateral margins of the male pleonal somite 6 ( Figs. 1C View Figure 1 , 2E View Figure 2 ) (vs. gently convex lateral margins of the male pleonal somite 6; Figs. 5C View Figure 5 , 6E View Figure 6 ). The gonopods and vulvae are quite different. The G1 of A. praecalvum sp. nov. can be differentiated from A. capillosum sp. nov. by being relatively stouter ( Fig. 3A, C View Figure 3 ) (vs. relatively more slender; Fig. 7A, C View Figure 7 ); the G1 terminal segment is more strongly bent at an angle of about 30° from the longitudinal axis ( Fig. 3A, C View Figure 3 ) (vs. only slightly bent at an angle of about 10° from the longitudinal axis; Fig.7A, C View Figure 7 ); the G1 terminal segment is relatively stouter and shorter, approximately 0.5 times the combined length of the flexible zone and the subterminal segment ( Fig. 3A–C View Figure 3 ) (vs. relatively slender and more elongate G1 terminal segment, approximately 0.6 times the combined length of the flexible zone and the subterminal segment; Fig.7A– C View Figure 7 ); and the G1 subterminal segment is gently sinuous, relatively stouter, basally broader and distally more narrow that forms a gentle shelf on the outer margin, which lacks a protuberance on the inner margin at the distal end ( Fig. 3A, C View Figure 3 ) (vs. distinctly more sinuous, relatively more slender, basally less broad and distally gradually narrower G1 subterminal segment that has a low rounded protuberance on the inner margin at the distal end; Fig. 7A, C View Figure 7 ). The G2 has a blunt tip and a stout basal segment at the proximal third in A. praecalvum sp. nov. ( Fig. 3D View Figure 3 ), whereas in A. capillosum sp. nov., it has a bifurcated tip and a stout basal segment at the proximal two-fifths ( Fig. 7D View Figure 7 ). The vulvae in A. praecalvum sp. nov. are located further apart (VD/SW = approximately 0.2), and the sternal vulvar cover is visible as a slightly raised plate ( Fig. 4C View Figure 4 ), while in A. capillosum sp. nov., the vulvae are relatively closer (VD/SW = approximately 0.1), and the sternal vulvar cover is obvious, the posterior part being only a flat surface ( Fig. 8D View Figure 8 ). In addition, the female telsons are different, being broadly ovate with a broad apex in A. praecalvum sp. nov. ( Fig. 4B View Figure 4 ) but broadly triangular with a relatively narrower apex in A. capillosum sp. nov. ( Fig. 8C View Figure 8 ).

Color in life. The carapace is purplish brown on the dorsal surface and yellowish brown on the ventral surface. The chelipeds and ambulatory legs are yellowish brown with purplish blotches. The setae are greyish-white.

Habitat. Abormon praecalvum sp. nov. was collected from shallow burrows adjacent to hilly streams, most of which flow through dense forest, at a relatively lower elevation (406–891 m a.s.l.) than that of the congener. Anthropogenic threats to these crabs are less likely as they live in a protected area.

Type locality. Mouling National Park, Abor Hills, Upper Siang District, Arunachal Pradesh, India.

Geographical distribution. Abormon praecalvum sp. nov. is currently known only from the Mouling National Park in the Upper Siang District of Arunachal Pradesh State, northeastern India.