Typhlocarcinus kerala, Ng, Peter K. L., Devi, Suvarna & Kumar, Appukuttannair Biju, 2017

Ng, Peter K. L., Devi, Suvarna & Kumar, Appukuttannair Biju, 2017, Typhlocarcinus kerala, a new species of rhizopine crab from southwestern India, and the identity of T. craterifer Rathbun, 1914 (Crustacea: Brachyura: Pilumnidae), Zootaxa 4272 (1), pp. 131-141 : 132-138

Typhlocarcinus kerala sp. nov.

( Figs. 3–6 , 7 D–I)

Material examined. Holotype: male (17.0 × 11.4 mm) (ZSI/ WGRC /IR-INV 8237) off Kerala coast, Kollam port, Thiruvananthapuram , Kerala , India, from trawls, coll. A.B. Kumar, 22 February 2013. Paratypes: 2 males (19.4 × 14.0 mm, 18.3 × 13.0 mm) , 2 females (19.6 × 13.0 mm, 13.2 × 9.0 mm) (DABFUK), same data as holotype.

Diagnosis. Carapace transversely subovate, male width 1.38–1.51 times length, female width 1.51 times length; dorsal surfaces smooth, covered with short pubescence on surface, with longer plumose setae on lateral and frontal margins, regions demarcated, H-shaped gastric and cardiac grooves deep, distinct, surface adjacent appears crenulated in adults; anterolateral margin strongly convex, lined with small granules, appears entire throughout length, granules at junction with posterolateral margin appear separated by very short groove but no clear tooth visible; posterolateral margins subparallel, straight, margin and surface evenly covered with small rounded granules ( Figs. 3 A–D, 4A–D). Frontal margin deflexed downwards, barely visible from dorsal view; bilobed with distinct median cleft, margin of each lobe distinctly convex ( Figs. 3 D, 4A–D). Orbit ovate; eyes small, with stout peduncle, small cornea, fused to carapace, immovable in male, mobile in female, tip with small spot of pigment ( Fig. 4 A–C). Posterior margin of epistome gently convex, not clearly divided into lobes ( Fig. 4 D). Outer surface of ischium, merus and exopod of third maxilliped with numerous small granules; anteroexternal angle of merus rounded; exopod slender ( Fig. 7 D). Chelipeds stout, inner angle of carpus with low or sharp granules; margins of carpus and merus with numerous granules and dense setae; chela stout, dorsal and ventral margins with numerous rounded granules and dense setae; cutting edges of propodal finger with prominent broad teeth ( Figs. 3 A–C, 4E, F, 5D, E). Ambulatory legs moderately short; propodus of last leg relatively short; dactylus of last leg straight from dorsal view, slightly curved on mesial view ( Figs. 3 B, C, 5A–C). Male pleonal locking tubercle peg-like, near anterior edge of sternite 5. Male pleon relatively narrow, telson triangular ( Fig. 6 A). Female pleon ovate; telson broadly triangular ( Fig. 6 D). G1 distinctly sinuous, distal part slender, curved, tapering to rounded tip ( Fig. 7 E–H). Vulva relatively large, ovate ( Fig. 6 F).

Variation. The carapace proportions of the five specimens vary rather substantially. The holotype male has a width to length ratio of 1.49, which is similar to that of two paratype females (1.46 and 1.51). The two paratype males (both larger than the holotype) are distinctly less broad, with a width to length ratio of 1.38 and 1.41, respectively. They, however, agree in all other characters, with the two males possessing the same structures of the front, anterolateral margin, pleon and G1. As such, we are confident they are conspecific. The H-shaped gastric and cardiac grooves are deep in the adult specimens but in the smallest female (13.2 × 9.0 mm) which is still subadult, these grooves are relatively shallower and less distinct. The condition of the eyes has been described as fused in many rhizopines but it is not easy to determine the condition in some. In T. kerala sp. nov., the eyes are immovable in one paratype male (18.3´13.0 mm) but slightly mobile in the holotype and other paratypes, and we are not sure if its due to the preservation as the specimens had been preserved in formalin which has made the carapaces relatively softer. The tip of the cornea, however, appears to have a tiny spot of pigment in all the specimens. Colour. In life, the carapace and appendages are white, with the fine pubescence and setae light brown. Etymology. The species is named after the state of Kerala in India. The name is used as a noun in apposition. Remarks. The specimens collected were light brown and covered with a fine brown sediment; suggesting that like many rhizopines, they are luteophilous in habits, i.e. living in mud and fine sediment, with the waters usually turbid (see Ng 1987b, 1990).

See General Discussion for taxonomic comments.

Figures

FIGURE 3. Typhlocarcinus kerala sp. nov. A, holotype male (17.0 × 11.4 mm) (ZSI / WGRC / IR-INV 8237); Kerala, India; B, D, paratype male (18.3 × 13.0 mm) (ZSI), Kerala, India; C, paratype female (19.6 × 13.0 mm) (DABFUK), Kerala, India. A – C, overall dorsal view; D, dorsal view of carapace right side (denuded).

FIGURE 4. Typhlocarcinus kerala sp. nov. A, E, paratype male (18.3 × 13.0 mm) (DABFUK), Kerala, India; B – D, F, paratype female (19.6 × 13.0 mm) (DABFUK), Kerala, India. A, C, D, frontal view of cephalothorax; B, right dorsal surface of carapace (denuded); E, F, outer view of chelae.

FIGURE 5. Typhlocarcinus kerala sp. nov., paratype male (18.3 × 13.0 mm) (DABFUK), Kerala, India. A, right last ambulatory leg; B, right second or third ambulatory leg; C, ventro-mesial view of second and fourth ambulatory dactyli and propodi; D, dorsal view of right cheliped; E, outer view of merus and carpus of right cheliped.

FIGURE 6. Typhlocarcinus kerala sp. nov. A – C, paratype male (18.3 × 13.0 mm) (DABFUK), Kerala, India; D – G, paratype female (19.6 × 13.0 mm) (DABFUK), Kerala, India; G, H, holotype male (17.0 × 11.4 mm) (ZSI / WGRC / IR-INV 8237), Kerala, India. A, anterior thoracic sternum, telson, and pleonal somites 5 and 6; B, E, thoracic sternum and pleonal somites 1 – 6; C, posterior thoracic sternum and pleonal somites 1 – 5; F, thoracic sternum and vulvae; G, lateral side of carapace showing granules; H, posterior thoracic sternites and sternopleonal cavity showing G 1, G 2 and pleonal locking tubercle on sternite 5.

FIGURE 7. A – C, Typhlocarcinus craterifer Rathbun, 1914, holotype female (13.4 × 9.5 mm) (USNM 46397), Philippines; D – I, Typhlocarcinus kerala sp. nov., paratype male (18.3 × 13.0 mm) (DABFUK), Kerala, India. A, right side of carapace (denuded); B, frontal margin (denuded); C, left third maxilliped (denuded); D, right third maxilliped (denuded); E, ventral view of left G 1; F, dorsal view of left G 1; G, ventral view of distal part of left G 1; H, dorsal view of distal part of left G 1; I, left G 2. Scales: A = 1.0 mm; B – I = 0.5 mm.