Gurumon gurumayum, Pati, 2022

Pati, Sameer K., 2022, Gurumon gurumayum, a new genus and new species of freshwater crab (Decapoda: Brachyura: Potamidae) from Arunachal Pradesh, northeastern India, European Journal of Taxonomy 847, pp. 28-45 : 38-42

Gurumon gurumayum sp. nov.

urn:lsid:zoobank.org:act:766FC0A2-3E63-4089-9949-CD72800E492F

Figs 1–4 , 6

Diagnosis

As for new genus.

Etymology

The species epithet is the family name of Dr Shantabala Devi Gurumayum, an Indian zoologist who kindly collected and provided the crab specimens for the present study. The species name is treated here as a Latin noun in apposition.

Material examined

Holotype INDIA – Arunachal Pradesh State • ♂, adult, CW 10.9 mm, CL 8.8 mm, CH 4.7 mm, FW 3.9 mm; Lower Dibang Valley District: Mayodia, Mehao Wildlife Sanctuary ; 28.233° N, 95.909° E; alt. 2473 m; 17 Oct. 2015; S.D. Gurumayum leg.; ZSI-WRC C.2170.

Paratypes INDIA – Arunachal Pradesh State • 1 ♂, adult, CW 13.3 mm, CL 9.9 mm, CH 5.6 mm, FW 4.6 mm; same collection data as for holotype; ZSI-WRC C.2171 • 1 ♀, adult, CW 12.7 mm, CL 10.0 mm, CH 5.9 mm, FW 4.4 mm; same collection data as for preceding; ZSI-WRC C.2171 • 1 ♀, adult, CW 13.1 mm, CL 9.9 mm, CH 5.6 mm, FW 4.2 mm; same collection data as for preceding; ZSI-WRC C.2172 • 1 ♀, adult, CW 12.6 mm, CL 9.5 mm, CH 5.7 mm, FW 4.0 mm; same collection data as for preceding; ZSI- WRC C.2172 .

Additional material

INDIA – Arunachal Pradesh State • 3 ♂♂, 4 ♀♀; Lower Dibang Valley District: near Mayodia Inspection Bungalow, Mehao Wildlife Sanctuary ; 28.235° N, 95.917° E; alt. 2513 m; 5 Sep. 2016; S.D. Gurumayum leg.; ZSI-WRC C.2173 .

Description of male holotype

Carapace transversely ovate, broader than long (CW/CL = 1.2), low ( CH /CW = 0.4); dorsal surface generally smooth, glabrous, conspicuously arched; anterolateral surface gently inflated in frontal view; anterolateral margins almost straight, subcristate, shorter than posterolateral margins; posterolateral margins converging posteriorly, almost straight medially; front broad (FW/CW = 0.3), strongly deflexed anteriorly, almost rectangular, anterior margin smooth, cristate, gently concave medially in dorsal view; epigastric cristae low, visible as 2 broad, rugose protuberances; postorbital cristae indiscernible; external orbital angle indistinct, low; epibranchial tooth very low, with very small cleft; postorbital region gently concave; branchial regions inflated; cervical grooves very shallow, narrow; mesogastric groove moderately deep, narrow, long, bifurcated posteriorly; H-shaped groove distinct; subhepatic region smooth, glabrous; suborbital region smooth, glabrous; pterygostomial region generally smooth, glabrous; supraorbital margin cristate, smooth, straight; suborbital margin cristate with low granules, almost straight on mesial half, curved upwards on lateral half, continuous with supraorbital margin; frontal medial triangle incomplete, with dorsal margin only, lateral margins indiscernible ( Figs 1A– C , 3A ). Epistome posterior margin with well-developed, narrowly triangular medial tooth and gently sinuous lateral margins ( Fig. 1B ).

Eyes occupying most of orbital space; eyestalk short, stout; cornea moderately large, pigmented ( Fig. 1B ).

Antennules short, folded in longitudinally broad fossae; antennae vestigial ( Fig. 1B ). Mandibular palp 3 segmented; terminal segment simple, undivided. First, second maxillipeds each with short 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 stout, tapered, reaching beyond anterolateral angle of ischium, completely lacking flagellum ( Figs 1B– C , 3B ).

Chelipeds smooth, glabrous, unequal, right chela larger ( Fig. 1A, C ). Major chela with 5 low, blunt teeth on each finger, distinct gape when fingers closed; dactylus gently curved, moderately stout, shorter than palm, smooth; palm longer than high, smooth; carpus smooth, gently inflated, with low, blunt inner distal tooth; merus smooth, lacking subterminal spine ( Fig. 1A, C ).

Ambulatory legs generally smooth, glabrous, slender, short, P3 longest; merus (P2–P5) elongated, lacking subdistal spine; dactylus (P2–P5) gently recurved, slightly longer than propodus, with distinct, sharp chitinous spines on margins ( Fig. 1A, C ).

Thoracic sternites punctate, glabrous; s1 and s2 completely fused; s2/s3 prominent, deep, narrow, gently sinuous, reaching lateral margins; s3/s4 indiscernible; s4/s5, s5/s6, s6/s7 shallow, narrow, indiscernible towards sternopleonal cavity; s7/s8 shallow, narrow, medially interrupted by longitudinal groove of s7, lacking transverse ridge; s8 completely covered by pleon, narrowed medially, longitudinal medial groove indiscernible ( Figs 1C , 3C ). Pleonal locking mechanism with prominent tubercle on submedial part of s5. Sternopleonal cavity deep, long, reaching to imaginary line joining submedial part of cheliped coxae ( Figs 1C , 3C ).

Pleon broad, triangular; pleonal somites 1–2 almost rectangular, narrower than pleonal somite 3; pleonal somite 3 subrectangular, broadest; pleonal somites 4–5 trapezoidal; pleonal somite 6 trapezoidal, distinctly broader than long (proximal width ca 3 × medial length), slightly longer than preceding pleonal somites, shorter than telson, with convex lateral margins ( Figs 1C , 3C–D ). Telson tongueshaped, broader than long (proximal width ca 1.5 × medial length), with concave lateral margins, apex broad, rounded ( Figs 1C , 3C–D ).

G1 stout, long, tip reaching up to s4/s 5 in situ; flexible zone small; terminal segment stout, cylindrical, long, ca 0.6 × combined length of flexible zone and subterminal segment, curved outwards at angle of about 30° from longitudinal axis, distal half gently upcurved, tip broad, blunt, dorsal flap absent; subterminal segment almost straight, stout, broad at base, relatively narrow distally, outer margin sinuous, inner margin almost straight; groove for G2 median ( Figs 3E , 4A–B ). G2 slightly longer than G1, ca 1.1 × as long as G1; distal segment gently curved, cylindrical, long, ca 0.4 × as long as basal segment, with blunt tip; basal segment stout at proximal third, appearing narrowly ovate ( Figs 3F , 4C ).

Remarks

The male paratype (ZSI-WRC C.2171) of Gurumon gurumayum sp. nov. is an adult and slightly larger in size than the male holotype. The male paratype shares most of the morphological features with the holotype except for its relatively broader carapace, CW/CL = 1.3 ( Fig. 2A ) (vs carapace relatively less broad, CW/CL = 1.2 in the holotype; Figs 1A , 3A ) and the straight s2/s3 ( Fig. 2C ) (vs s2/s3 gently sinuous in the holotype; Figs 1C , 3C ).

The female paratypes (ZSI-WRC C.2171, 2172) of Gurumon gurumayum sp. nov. are adults and slightly larger than the male holotype. All the female paratypes possess most of the non-sexual character states as those in the male holotype. Their carapace, however, is relatively broader, CW/CL = 1.3 ( Fig. 2E, H ) like that of the male paratype. All the female paratypes have subequal chelipeds ( Fig. 2E, H ) unlike the unequal chelipeds of the holotype and paratype males ( Figs 1A, C , 2A ). The pleonal somites and telson of the female paratypes are ovate in shape, which cover the thoracic sternum except for lateral edges when closed ( Fig. 2F ). Their pleonal somite 1 is the shortest; pleonal somites 2–5 are progressively longer; and pleonal somite 6 is the longest, much broader than long, subequal in length to the telson, with the convex lateral margins ( Fig. 2F ). The telson in the female paratypes is broadly triangular, much broader than long, with convex lateral margins and narrow apex ( Fig. 2F ). The vulvae in female paratypes are located apart from each other (VD/SW = ca 0.25) on s6, each opens mesially, subovate, large, occupying three-quarters the length of s6, touching but not pushing s5/s6 anteriorly, and covered by soft membranous operculum ( Fig. 2G ).

Colour in life

The cephalothorax is dark purple; the chelipeds are generally reddish brown with dark purplish-brown upper surface; and the ambulatory legs are light brown with dark purple blotches ( Fig. 6 ).

Ecological notes

Gurumon gurumayum sp. nov. was found among the moss-covered stones in the shallow (ca 10 cm deep) and slow-flowing brooks of the subalpine forests of Mayodia during September and October. Located within the Mehao Wildlife Sanctuary, Mayodia is situated in the Mayu hills of the Lower Dibang Valley District of Arunachal Pradesh, which is about 56 km from the district headquarters at Roing. The new species is known to dwell at 2473–2513 m altitude and seems restricted to the high mountains. These crabs are very unlikely to be found during the winter season (Nov.–Feb.) as Mayodia experiences snowfall. Their activities, however, resume during the summer (Mar.–Jun.) (S.D. Gurumayum, personal communication).

Geographical distribution

Gurumon gurumayum sp. nov. is currently known only from two adjacent localities of the Mehao Wildlife Sanctuary in the Lower Dibang Valley District of Arunachal Pradesh State, northeastern India ( Fig. 5 ).

Figures

Fig. 1. Gurumon gurumayum gen. et sp. nov., holotype (ZSI-WRC C.2170), ♂ (CW 10.9 × CL 8.8 mm). A. Entire animal, dorsal view. B. Cephalothorax, frontal view. C. Entire animal, ventral view. Scale bars: A, C = 5 mm; B = 2 mm.

Fig. 2. Gurumon gurumayum gen. et sp. nov. A–D. Paratype (ZSI-WRC C.2171), ♂ (CW 13.3 × CL 9.9 mm). E–G. Paratype (ZSI-WRC C.2171), ♀ (CW 12.7 × CL 10.0 mm). C. Paratype (ZSI-WRC C.2172), ♀ (CW 12.6 × CL 9.5 mm). A, E, H. Entire animal, dorsal view. B. Mandibular palp, dorsal view. C. Thoracic sternites with G1 and G2 in situ. D. Posterior thoracic sternites (s5–s8). F. Pleonal somites 3–6 and telson. G. Thoracic sternites showing vulvae. Scale bars: A, E, H = 5 mm; C–D, F–G = 2 mm; B = 0.5 mm.

Fig. 3. Gurumon gurumayum gen. et sp. nov., holotype (ZSI-WRC C.2170), ♂ (CW 10.9 × CL 8.8 mm). A. Cephalothorax, dorsal view. B. Third maxilliped (left). C. Thoracic sternites (s1–s7), pleonal somites 3–6 and telson. D. Pleon and telson. E. G1 (left), dorsal view. F. G2 (left). Scale bars: A, C–D = 2 mm; B, E–F = 1 mm.

Fig. 4. Gurumon gurumayum gen. et sp. nov., holotype (ZSI-WRC C.2170), ♂ (CW 10.9 × CL 8.8 mm). A. G1 (left), dorsal view. B. G1 (left), ventral view. C. G2 (left). Scale bars = 1 mm.

Fig. 6. Gurumon gurumayum gen. et sp. nov., paratype (ZSI-WRC C.2171), ♂ (CW 13.3 × CL 9.9 mm), colour in life.

Fig. 5. Map showing India, China and distribution of the species of Gurumon gen. nov., Abormon Mitra, Pati & Ng, 2021, Pararanguna Dai & Chen, 1985, and Potamiscus Alcock, 1909.