Abormon capillosum, Ng, 2021

Abormon capillosum View in CoL sp. nov.

( Figs. 5–8 View Figure 5 View Figure 6 View Figure 7 View Figure 8 , 9A View Figure 9 )

Zoobank: urn:lsid:zoobank.org:act:38569927-AFFE-42B3-991C-304C2D36F644

Type material. Holotype: male ( CW 10.2 mm, CL 8.5 mm, CH 4.4 mm, FW 3.5 mm), Tulung Village , near Tutting , Abor Hills, Upper Siang District, Arunachal Pradesh, India (29.006°N 94.897°E), altitude 1240 m a.s.l., 5 November 2019, coll. S. Mitra ( ZSIK C.8610/2) GoogleMaps . Paratypes: 1 male ( CW 12.2 mm, CL 10.1 mm, CH 4.9 mm, FW 4.2 mm), same data as holotype ( ZSIK C.8611/2) GoogleMaps ; 1 female ( CW 14.5 mm, CL 11.8 mm, CH 6.3 mm, FW 5.1 mm), same data as holotype ( ZSIK C.8612/2) GoogleMaps .

Diagnosis. Small species (CW <15 mm). Carapace ovate, broader than long (CW/CL = 1.2), relatively low ( CH /CW = 0.4); dorsal surface densely setose; epistome posterior margin with rounded to triangular medial tooth,concave lateral margins ( Figs. 5A, B View Figure 5 , 6A View Figure 6 , 8A, B View Figure 8 , 9A View Figure 9 ). Chelipeds densely setose, with relatively narrow inner distal major tooth on carpus ( Figs. 5A, C View Figure 5 , 6C View Figure 6 , 8A View Figure 8 , 9A View Figure 9 ). Ambulatory legs densely setose ( Figs. 5A, C View Figure 5 , 8A View Figure 8 , 9A View Figure 9 ). Male pleon broad, triangular, with gently concave lateral margins; pleonal somite 6 trapezoidal, with gently convex lateral margins ( Figs. 5C View Figure 5 , 6E View Figure 6 ). G1 relatively slender, with terminal segment gently curved outwards at angle approximately 10° from longitudinal axis; terminal segment relatively slender and long, approximately 0.6 times combined length of flexible zone and subterminal segment, dorsal flap low, broadly rounded, medially located; subterminal segment distinctly sinuous, relatively slender, less broad basally, gradually narrow distally, with low, rounded protuberance on inner margin at distal end ( Figs. 6D View Figure 6 , 7A–C View Figure 7 ). G2 1.2 times G1 length; distal segment long, approximately 0.5 times length of basal segment, with bifurcated tip; basal segment stout at proximal two-fifths ( Fig. 7D View Figure 7 ). Female telson broadly triangular, with relatively narrow apex ( Fig. 8C View Figure 8 ). Vulvae located close to each other (VD/SW = approximately 0.1); posterior sternal vulvar cover not raised, relatively flat ( Fig. 8D View Figure 8 ).

Description of male holotype. Carapace small (CW 10.2 mm), transversely ovate, broader than long (CW/CL = 1.2), low ( CH /CW = 0.4); dorsal surface gently convex in frontal view, rugose, punctate, densely 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 2.5 times length of inner margin; epibranchial tooth very low, with very small cleft; postorbital region gently concave; branchial regions gently inf lated; cervical grooves barely visible; mesogastric groove deep, narrow, long, bifurcated posteriorly; H-shaped groove distinct; subhepatic region almost smooth, setose; suborbital region generally smooth, sparsely setose; supraorbital margin gently concave medially, cristate with low granules; suborbital margin concave, cristate with low granules, confluent 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, broad, rounded medial tooth, concave lateral margins ( Fig. 5A–C View Figure 5 ). Eyes occupying most of orbital space; eyestalk short, stout; cornea moderately large, pigmented ( Fig. 5B View Figure 5 ).

Antennules long, folded in transversely broad fossae; antennae very short, reaching slightly beyond base of eyestalk ( Fig. 5B View Figure 5 ). Mandibular palp 3-segmented; terminal segment simple, undivided. First, second maxillipeds each with long flagellum 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 ( Fig. 5B, C View Figure 5 ).

Chelipeds rugose, densely setose, subequal, left chela slightly larger ( Fig. 5A, C View Figure 5 ). Major chela with 4 or 5 large, sharp teeth on each finger, small 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 inflated, with narrow, sharp, triangular inner distal major tooth and very low, blunt sub-basal tooth; merus slightly rugose on outer surface, without subterminal spine ( Fig. 5A, C View Figure 5 ).

Ambulatory legs moderately stout, short, P3 longest, densely 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. 5A, C View Figure 5 ).

Thoracic sternites punctate, sparsely setose; S1/S2 short; S2/S3 distinct as deep, narrow, straight 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 ( Fig. 5C View Figure 5 ). Pleonal locking mechanism with prominent tubercle on medial part of S5. Sternopleonal cavity deep, long, reaching to imaginary line joining anterior part of cheliped coxae ( Fig. 5C View Figure 5 ).

Pleon broad, triangular, with gently concave lateral margins; pleonal somites 1, 2 almost rectangular, narrower than pleonal somite 3; pleonal somites 3–5 trapezoidal; pleonal somite 6 trapezoidal, broader than long (proximal width approximately 2.3 times medial length), distinctly longer than preceding pleonal somites, distinctly shorter than telson, with gently convex lateral margins ( Fig. 5C View Figure 5 ). Telson tongue-shaped, broader than long (proximal width approximately 1.3 times medial length), with concave lateral margins, apex broad, rounded ( Fig. 5C View Figure 5 ).

G1 slender, sinuous, with terminal segment gently curved outwards at angle of about 10° from longitudinal axis, tip blunt tapering, reaching beyond pleonal locking tubercle up to S4/S 5 in situ; flexible zone large; terminal segment moderately stout, conical, long, approximately 0.6 times combined length of flexible zone and subterminal segment, dorsal flap distinct but low, broadly rounded, medially located, not reaching proximal end; subterminal segment sinuous, slender, broad at base, gradually narrow distally, with distinct, rounded protuberance on inner margin at distal end; groove for G2 median ( Fig. 7A–C View Figure 7 ). G2 longer than G1, approximately 1.2 times G1 length; distal segment straight, cylindrical, long, approximately 0.5 times length of basal segment, with bifurcated tip; basal segment stout at proximal two-fifths, appearing narrowly ovate ( Fig. 7D View Figure 7 ).

Paratypes. The male paratype ( ZSIK C.8611/2) is slightly larger ( CW 12.2 mm) than the holotype but agrees with it in all the diagnostic characters. The male paratype, however, has the dorsal surface of the carapace relatively less granulated, less punctate, and with fewer setae ( Fig. 6A View Figure 6 ). The S 2/S 3 in the male paratype is concave ( Fig. 6D View Figure 6 ) whereas it is straight in the holotype ( Fig. 5C View Figure 5 ). Also, the pleonal somite 6 in the male paratype is relatively broader (proximal width approximately 2.4times the medial length) ( Fig. 6E View Figure 6 ) against the relative narrower (proximal width approximately 2.3 times the medial length) pleonal somite 6 of the holotype ( Fig. 5C View Figure 5 ). The differences, however, are not substantial; their G1 structures being identical .

The female paratype (ZSIK C.8612/2) is larger (CW 14.5 mm) than the holotype and the male paratype but share most of the non-sexual characters. The medial tooth on the posterior margin of the epistome in the female paratype is relatively narrower and triangular ( Fig.8B View Figure 8 ), but this structure is relatively broader and rounded in the holotype ( Fig. 5B View Figure 5 ) and the male paratype. The pleon of the female paratype is narrowly ovate, which covers the thoracic sternum except for S1, S2, and lateral edges when closed ( Fig. 8C View Figure 8 ). 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. 8C View Figure 8 ). The telson of the female paratype is broadly triangular, much broader than long, with gently convex lateral margins and narrow apex ( Fig. 8C View Figure 8 ). The vulvae on S6 are close to each other (VD/SW= approximately 0.1), open anteriorly, transversely ovate, relatively small, occupying half the length of S6, anterior margin touching S5/S6, and the posterior sternal vulvar cover is not raised and relatively flat ( Fig. 8D View Figure 8 ).

Etymology. The species name is derived from the Latin ‘ capillosus ’ for very hairy, alluding to the dense setae covering the carapace and pereiopods of the crab.

Remarks. Abormon capillosum sp. nov. is easily distinguished from the only congener, A. praecalvum sp. nov. (see remarks for latter species).

Color in life. The carapace is light grey with dark purplish brown patches on the dorsal surface and yellowish brown on the ventral surface ( Fig.9A View Figure 9 ). The chelipeds and ambulatory legs are light brown with purplish blotches ( Fig. 9A View Figure 9 ). The setae are greyish-white ( Fig. 9A View Figure 9 ).

Habitat. Abormon capillosum sp. nov. is found in primary montane dipterocarp forests at a relatively high elevation (1240 m a.s.l.). Individuals were found in burrows of soft mud, next to eroded stones, adjacent to a narrow and almost dried stream that is connected to the Siang River ( Fig. 9B View Figure 9 ). The crabs retreated into their shallow burrows (depth up to 10 cm) when disturbed. The habitat is pristine and almost free from anthropogenic disturbances.

Type locality. Tutting, Abor Hills, Upper Siang

District, Arunachal Pradesh, India.

Geographical distribution. Abormon capillosum sp. nov. is currently known only from the type locality, i.e., Tutting in the Upper Siang District of Arunachal Pradesh State, northeastern India .