Karkata, Pati & Rajesh & Raj & Sheeja & Kumar & Sureshan, 2017

Pati, S. K., Rajesh, L., Raj, Smrithy, Sheeja, V. U., Kumar, A. Biju & Sureshan, P. M., 2017, Karkata, a new genus of gecarcinucid freshwater crab with two new species, and four new species of Pilarta Bahir and Yeo, 2007 and Cylindrotelphusa Alcock, 1909 (Decapoda: Brachyura) from Kerala, India, Journal of Natural History (J. Nat. Hist.) 51 (23 - 24), pp. 1295-1330 : 1297-1301

Karkata gen. nov.

Type species

Karkata ghanarakta sp. nov., by present designation.

Diagnosis

Carapace slightly broader than long (cw/cl = ca. 1.3), deep (ch/cl = ca. 0.6–0.7); dorsal surface slightly convex in frontal view, smooth except epigastric and postorbital cristae, and lateral margins; frontal margin almost straight, slightly broad (fw/cw = ca. 0.3); epigastric and postorbital cristae well developed; external orbital angle acutely triangular, with short outer margin, ca. 2 times length of inner margin; epibranchial tooth small, blunt; cervical grooves distinct; H-shaped groove deep; frontal median triangle incomplete, with cristate dorsal margin only; epistome posterior margin with prominent, triangular median lobe ( Figures 2 (a,b) and 4(a,b)). Chelipeds with outer surface of carpus rugose. Ambulatory legs with scattered setae ( Figures 2 (a,f) and 4(a,f)). Sutures between male thoracic sternites s2/s3 and s3/s4 prominent as deep grooves ( Figures 2 (c,g) and 4 (c,g)). Male abdomen T-shaped; sixth abdominal somite nearly as long as broad, longer than telson; telson as long as broad ( Figures 2 (c,h) and 4(c,h)). Mandibular palp with 2 segments, terminal segment bilobed. Third maxilliped exopod longer than ischium, lacking flagellum ( Figures 2 (i) and 4(i)). G1 almost straight; terminal segment coneshaped, very short, ca. 0.2 times length of subterminal segment; subterminal segment with almost straight inner margin ( Figures 3 (a–c) and 5(a–c)). G2 with short distal segment, ca. 0.3 times length of basal segment ( Figures 3 (d) and 5(d)).

Etymology

The genus name, Karkata , means ‘crab’ in Sanskrit and Malayalam. Gender feminine. Used as a noun in apposition.

Remarks

Karkata gen. nov. is distinguished from all other Indian gecarcinucid genera by the following suite of carapace and gonopod characters: a moderately arched, smooth carapace, a broad frontal margin (fw/cw = ca. 0.3), well developed epigastric and postorbital cristae, an acutely triangular external orbital angle, a prominent suture between the male thoracic sternites s2/s3 and s3/s4, the absence of a flagellum on the third maxilliped exopod, a very short G1 terminal segment, ca. 0.2 times the length of the subterminal segment, and a short G2 distal segment, ca. 0.3 times the length of the basal segment ( Figures 2 (a–c,g,i), 3(a,d), 4(a–c,g,i) and 5(a,d)).

Karkata lacks a flagellum on the third maxilliped exopod like that of Globitelphusa Alcock, 1909 , Liotelphusa Alcock, 1909 , Arcithelphusa Pati and Sudha Devi, 2015a , Ghatiana Pati and Sharma, 2014 , Gubernatoriana Bott, 1970 , Inglethelphusa Bott, 1970 , Pilarta Bahir and Yeo, 2007 and Snaha Bahir and Yeo, 2007 . Karkata , however, is differentiated from Globitelphusa and Liotelphusa mainly by the inner margin of the G1 subterminal segment that is not angled and is not sharply tapering ( Figures 3 (a–c) and 5(a–c)) (vs distinctly angled and sharp tapering of the inner margin of the G1 subterminal segment; see Bott 1970, pl. 33, fig. 15 for Globitelphusa ; pl. 27, fig. 28 for Liotelphusa ). The new genus can be distinguished from Arcithelphusa by its moderately arched carapace, relatively broad front and almost straight G1 terminal segment ( Figures 2 (a,b), 3(a–c), 4(a,b) and 5(a–c)) (vs highly arched carapace, relatively narrow front and prominently curved G1 terminal segment; see Pati and Sudha Devi 2015a, figs 2(a,b,d–f) and 3(b,f,h)). Karkata is differentiated from Ghatiana , Gubernatoriana , Inglethelphusa and Pilarta by the prominent suture between the male thoracic sternites s2/s3 and s3/s4 ( Figures 2 (c,g) and 4(c,g)) (vs undiscernible suture between the male thoracic sternites s2/s3 and s3/s4; see Bott 1970, pl. 34, fig. 26 for Inglethelphusa ; Bahir and Yeo 2007, fig. 25(c) for Pilarta ; Pati and Sharma 2014, fig. 3(a) for Ghatiana , fig. 7(a) for Gubernatoriana ). The new genus can also be distinguished from Pilarta by a significant suite of characters: well developed epigastric and postorbital cristae, acutely triangular external orbital angle, with short outer margin, ca. 2 times the length of the inner margin, deep H-shaped groove, ambulatory legs lacking dense setae on the external surfaces of the dactylus, propodus and carpus, very short G1 terminal segment, ca. 0.2 times the length of the subterminal segment, and short G2 distal segment, ca. 0.3 times the length of the basal segment ( Figures 2 (a,f), 3(a,d), 4(a,f) and 5(a,d)) (vs visible, but not well developed epigastric and postorbital cristae, broadly triangular external orbital angle, with long outer margin, ca. 3–4 times the length of the inner margin, shallow H-shaped groove, ambulatory legs with dense setae on the external surfaces of the dactylus, propodus and carpus, relatively long G1 terminal segment, ca. 0.3 times the length of the subterminal segment, and long G2 distal segment, ca. 0.4–0.5 times the length of the basal segment; see Bahir and Yeo 2007, figs 25 (a,e,f,h) and 26(a)).

Karkata and Snaha have many similarities in carapace morphology, particularly in lacking dense setae on the ambulatory legs and having a prominent suture between the male thoracic sternites s2/s3 and s3/s4 ( Figures 2 (c,f,g) and 4(c,f,g); see Bahir and Yeo 2007, figs 28(a,c), 29(a) and 30(a,c)). However, Karkata can be easily differentiated from Snaha by its well developed epigastric and postorbital cristae, acutely triangular external orbital angle, with short outer margin, ca. 2 times the length of the inner margin, distinct cervical grooves, deep H-shaped groove, very short G1 terminal segment, ca. 0.2 times the length of the subterminal segment, almost straight inner margin of the G1 subterminal segment, and short G2 distal segment, ca. 0.3 times the length of the basal segment ( Figures 2 (a), 3(a,d), 4(a) and 5(a,d)) (vs indistinct epigastric and postorbital cristae, broadly triangular external orbital angle, with long outer margin, ca. 3–4 times the length of the inner margin, indistinct cervical grooves, shallow H-shaped groove, relatively long G1 terminal segment, ca. 0.3 times the length of the subterminal segment, sinuous inner margin of the G1 subterminal segment, and long G2 distal segment, ca. 0.4–0.5 times the length of the basal segment; see Bahir and Yeo 2007, figs 27(c,g), 28 (a), 29(c,e) and 30(a)).

Karkata gen. nov. comprises two new species: K. ghanarakta sp. nov. (type species) and K. kusumbha sp. nov.

Ecological notes

Crabs of the genus dwell under cobblestones of small streams as well as in loose soil burrows in riparian habitats or underneath boulders of rocky terrain. Crabs were collected at different altitudes ranging from 58 to 793 m.

Geographic distribution

The genus is endemic to the Western Ghats of Kerala . The type species, Karkata ghanarakta sp. nov., is found in a protected area (i.e. the Thattekkad Bird Sanctuary of Ernakulam district) whereas Karkata kusumbha sp . nov. is known only from its type locality, Thaalumkandam of Idukki district .

Figures

Figure 2. Karkata ghanarakta gen. et sp. nov., holotype male (ZSI, WRC-C.1523). (a) Dorsal view; (b) frontal view; (c) ventral view; (d) right or major cheliped; (e) carpus of major cheliped; (f) right ambulatory leg (p3); (g) anterior thoracic sternites (s1–s4); (h) abdominal somites 5, 6 and telson; (i) left third maxilliped. Scale bars: a–c = 10 mm; d, f = 5 mm; e, g–i = 2 mm.

Figure 3. Karkata ghanarakta gen. et sp. nov., holotype male (ZSI, WRC-C.1523). (a) Dorsal view of left G1; (b) dorsal view of left G1 terminal segment; (c) ventral view of left G1; (d) left G2. Scale bars: a, c, d = 1 mm; b = 0.5 mm.