Spiralothelphusa gibberosa, Pati, S. K. & Sudha Devi, A. R., 2015

Pati, S. K. & Sudha Devi, A. R., 2015, Spiralothelphusa gibberosa, a new freshwater crab (Brachyura: Gecarcinucidae) from Thrissur district, Kerala, India, Zootaxa 3963 (3), pp. 416-424 : 418-422

Spiralothelphusa gibberosa n. sp.

( Figs. 2 , 3 , 4 )

Type material. INDIA: adult male, holotype (cw 28.04 mm, cl 22.96 mm, ch 14.02 mm, fw 8.24 mm), Kizhoor, 2 km north west of Kunnamkulam, Thrissur district, Kerala (10.6549906° N and 76.0551461° E), altitude 56 m, 30 December 2013, coll. Preman (ZSI, WRC-C.1186); paratypes, male (cw 27.88 mm, cl 22.56 mm, ch 14.00 mm, fw 9.96 mm) and female (cw 30.38 mm, cl 24.70 mm, ch 16.20 mm, fw 11.40 mm), same collection data as holotype (ZSI, WRC-C.1187).

Diagnosis. Carapace broad, smooth; anterolateral margin strongly convex; frontal margin 0.3 to 0.4 times carapace width, slightly concave at middle portion; epigastric cristae distinct, anterior to postorbital cristae; postorbital cristae sharp, distinctly curved, sloping posteriorly towards postorbital region, anteriorly towards lateral border; outer margin of external orbital angle twice in length to inner margin; epibranchial tooth distinct, sharp, slightly elevated from level of postorbital cristae; branchial regions inflated; frontal median triangle complete; epistomal median lobe with acute tooth; suture between male thoracic sternites S2, S3 hardly discernible, S3, S4 indiscernible; male abdomen narrowly triangular; sixth male abdominal somite broader than long, equal in length to telson, with slightly concave lateral margins ( Figs. 2 A–C, 3A–D). G1 stout, with longitudinally twisted, long, distal portion, two-third length of non-twisted portion, twisted half turn clockwise, with numerous hairs, directed outwards; tip of twisted portion straight; non-twisted portion broad with distinctly setose hump on outer margin ( Figs. 4 A–C). G2 with long distal segment, 0.4 times length of basal segment ( Fig. 4 D).

Description of holotype. Carapace broad, prominently arched (ch/cw = 0.5), smooth; anterolateral margin strongly convex, first oblique striae on branchial region originates as cristae of anterolateral border, curving into branchial region at base of epibranchial region, strongest striae on lateral border; posterolateral margin with few fine, oblique, short striae; frontal margin narrow, one third of carapace width (fw/cw = 0.3), slightly concave at middle; epigastric cristae well developed, sharp, straight, anterior to postorbital cristae; postorbital cristae sharp, distinctly curved, sloping posteriorly towards postorbital region, anteriorly towards lateral border; external orbital angle outer margin twice in length to inner margin; epibranchial tooth distinct, sharp, slightly elevated from level of postorbital cristae, far from level of supraorbital margin; postorbital region deep; branchial regions inflated; cervical grooves shallow, narrow, clearly interrupted, not reaching up to level of postorbital cristae; H-groove faintly visible; frontal median triangle complete, not as broad as frontal margin, dorsal margin not fused with lateral margins; epistomal median lobe with acute tooth ( Figs. 2 A,B, 3A,B).

Chelipeds smooth; right chela slightly bigger than left chela; finger tips pointed, teeth on them smaller, coarser; carpal spine distinct, sharp; outer surface of merus slightly rugose ( Figs. 2 A–C). Ambulatory legs (P2–P5) long, smooth, dactylus equal in length to propodus; longest propodus (P4) thrice as long as broad ( Figs. 2 A–C).

Suture between male thoracic sternites S2, S3 hardly discernible, S3, S4 indiscernible ( Figs. 2 C, 3C).

Male abdomen narrowly triangular; sixth abdominal somite broader than long, equal in length to telson, with slightly concave lateral margins; telson broad, bell-shaped, apex nearly round; male sternoabdominal cavity deep, reaching imaginary line joining middle of bases of chelipeds ( Figs. 2 C, 3D).

Mandibular palp with two segments, terminal segment bilobed. Exopods of maxillipeds each with long flagellum; third maxilliped exopod longer than ischium, reaching outer half of merus, ventral sulcus of ischium deep, towards and almost parallel to inner margins, depression on merus towards inner sides ( Fig. 3 E).

G1 stout, with longitudinally twisted, long, distal portion, two-third length of non-twisted portion, twisted half turn clockwise, with numerous hairs, directed outwards; tip of twisted portion straight; non-twisted portion very broad with distinctly setose hump on outer margin ( Figs. 4 A–C). G2 with long distal segment, 0.4 times length of basal segment ( Fig. 4 D).

Colour. Carapace, chelipeds, ambulatory legs yellowish brown to brown with reddish brown spots on dorsal sides only.

Type Locality. Kizhoor, 2 km north west of Kunnamkulam, Thrissur district, Kerala, India (10.6549906° N and 76.0551461° E) (altitude 56 m).

Paratypes. The male paratype (ZSI, WRC-C.1187) agrees well with the holotype in G1 structure and carapace morphology except for its slightly broad frontal margin (fw/cw = 0.4), distinct oblique, short striations on posterolateral margin, and almost equal sized chelipeds. The female paratype (ZSI, WRC-C.1187) also has a broad front, distinct striations on posterolateral margin, and equal sized chelipeds. Anterolateral carapace of the female paratype is more convex than that of the holotype and the male paratype. Paratype specimens are darker in colour than the holotype.

Distribution. The species is known only from the type locality, Kizhoor and Thrissur.

Habitat. Specimens were found in rice fields ( Fig. 5 A), collected from shallow burrows along rice field bunds. Spiralothelphusa gibberosa n. sp. is also found in burrows along canal embankments ( Fig. 5 B, C).

Etymology. The species name is derived from the Latin for prominently humped, alluding to the hump-like outer margin of the non-twisted portion of the first male pleopod.

Remarks. Spiralothelphusa gibberosa n. sp. resembles its congeners in many structural features of the carapace: convex dorsal surface, inflated branchial regions, first oblique striae on branchial regions originating as cristae of anterolateral border, sharp epibranchial tooth situating slightly above level of postorbital cristae, distinct postorbital cristae, external orbital tooth outer margin slightly longer than inner margin, concave postorbital region, complete frontal median triangle with cristate dorsal margin, not fused with lateral margins, epistomal median lobe with acute median tooth, indistinct suture between thoracic sternites 2, 3 and 3, 4, and stout, almost triangular male abdomen with concave lateral borders [ Figs. 2 A–C, 3A–D for S. gibberosa n. sp.; Fernando 1961: figs. 1A, B, pl. 1A, B for S. parvula ; Ng & Tay 2001: figs. 23A, B, F, 25A, B for S. wuellerstorfi , figs. 26A, B, E for S. senex , figs. 29A, B, E, 30A–C for S. fernandoi , figs. 31F, G for S. hydrodroma , figs. 32A–C, F, 33A, B for S. parvula ; Pati & Sharma 2014: pl. XI, figs. 11A–C for S. wuellerstorfi (see comments on corrected identification of S. hydrodroma reported from Maharashtra)]. Only the G1 structure is reliable for species diagnosis (Ng & Tay 2001). Some carapace features are nevertheless unique among the members of Spiralothelphusa . For instance, the postorbital cristae of S. parvula and S. wuellerstorfi is almost straight, gently sloping posteriorly towards lateral border ( Fernando 1961: fig. 1A, pl. 1A, B for S. parvula ; Ng & Tay 2001: figs. 23A, 25A for S. wuellerstorfi , figs. 32A, B, 33A for S. parvula ; Pati & Sharma 2014: pl. XI, fig. 11A for S. wuellerstorfi ), whereas the remaining species have distinctly concave postorbital cristae, sloping posteriorly towards postorbital region and then anteriorly towards lateral border ( Figs. 2 A, 3A for S. gibberosa n. sp.; Ng & Tay 2001: fig. 26A for S. senex , figs. 29A, 30A, C for S. fernandoi , fig. 31F for S. hydrodroma ). All the members of Spiralothelphusa have a strongly convex anterolateral margin, whereas S. parvula has a gently convex to almost straight anterolateral margin ( Fernando 1961: fig. 1A, pl. 1A, B; Ng & Tay 2001: fig. 33A). Among the species of Spiralothelphusa , only S. fernandoi has a very low subbasal granule on the chelipedal carpus in addition to a pointed inner distal spine (Ng & Tay 2001: fig. 29D). The sub-basal granules are nevertheless barely visible in juveniles (Ng & Tay 2001). The shape of the male abdomen is similar among the species of Spiralothelphusa . The telson of S. wuellerstorfi is nonetheless slightly longer than the sixth male abdominal somite ( Pati & Sharma 2014: pl. XI, fig. 11C).

Spiralothelphusa gibberosa n. sp. resembles S. parvula from Sri Lanka in having a G1 non-twisted portion with setose hump on the outer margin ( Figs. 4 A, B; Fernando 1961: fig. 1D; Ng & Tay 2001: fig. 32G). Both species can be distinguished from each other by terminal segment and distal portion of subterminal segment, which are less strongly twisted in S. gibberosa n. sp. ( Figs. 4 A–C) and strongly twisted in S. parvula ( Fernando 1961: figs. 1D, E; Ng & Tay 2001: figs. 32G, I–K). The G1 twisted portion of S. gibberosa n. sp. is long, two-third length of non-twisted portion ( Figs. 4 A–C), whereas the G1 twisted portion of S. parvula is comparatively short, half length of non-twisted portion ( Fernando 1961: fig. 1D; Ng & Tay 2001: figs. 32G, I). The major difference between these two species is the shape of the G1 terminal segment. The G1 terminal segment is conical and the tip is straight in S. gibberosa n. sp. ( Figs. 4 A, B), whereas the G1 terminal segment is sinuous and the tip is distinctly upcurved in S. parvula ( Fernando 1961: fig. 1D; Ng & Tay 2001: figs. 32G, I–K).

The new species is also similar to the Indian species, S. wuellerstorfi in their G1 structure. Both species have a long twisted portion, two-third length of non-twisted portion ( Fig. 4 A; Ng & Tay 2001: figs. 23I, 24B, I; Pati & Sharma 2014: pl. XI, figs. 11D, E). In S. wuellerstorfi , however, the terminal segment and the distal portion of the subterminal segment are strongly twisted like that of S. parvula , and the hump is absent on the outer margin of the non-twisted portion of the G1 unlike S. parvula and S. gibberosa n. sp. ( Figs. 4 A–C for S. gibberosa n. sp.; Fernando 1961: figs. 1D, E for S. parvula ; Ng & Tay 2001: figs. 23G, I–K, 24A–F, H–K for S. wuellerstorfi , figs. 32G, I for S. parvula ; Pati & Sharma 2014: pl. XI, figs. 11D, E for S. wuellerstorfi ). The G1 terminal segment of S. gibberosa n. sp. is conical with straight tip ( Figs. 4 A, B), whereas S. wuellerstorfi and S. parvula have a sinuous G1 terminal segment with the tip either gently hooked downwards as in S. wuellerstorfi or upcurved as in S. parvula ( Fernando 1961: fig. 1D for S. parvula ; Ng & Tay 2001: figs. 23G, I–K, 24A–F, H–K for S. wuellerstorfi , figs. 32G, I–K for S. parvula ; Pati & Sharma 2014: pl. XI, figs. 11D, E for S. wuellerstorfi ).

The new species is clearly differentiated from S. hydrodroma by the long distal segment of its G2, 0.4 times the length of the basal segment ( Fig. 4 D) as opposed to the short distal segment of the G2, 0.25 times the length of the basal segment (Ng & Tay 2001: fig. 31C). The G1 terminal segment tip is straight in S. gibberosa n. sp. ( Figs. 4 A, B), whereas the G1 terminal segment tip is gently curved upwards in S. hydrodroma (Ng & Tay 2001: figs. 31A, B, D, E). The G1 terminal segment tip is straight in both S. gibberosa n. sp. and S. fernandoi ( Figs. 4 A, B for S. gibberosa n. sp.; Ng 1994: figs. 1B–E for S. fernandoi ; Ng & Tay 2001: figs. 29F, H–K for S. fernandoi ), whereas the G1 terminal segment tip is gently curved downwards or almost straight in S. senex (Ng & Tay 2001: figs. 27A– C). Nevertheless, the most unique feature in S. gibberosa n. sp. is the presence of setose hump on outer margin of the G1 non-twisted portion ( Figs. 4 A, B). The hump on outer margin of the non-twisted portion is absent in S. fernandoi , S. hydrodroma , and S. senex (Ng 1994: figs. 1B, C for S. fernandoi ; Ng & Tay 2001: figs. 27A, B for S. senex , figs. 29F, H for S. fernandoi , figs. 31A, B for S. hydrodroma ). Spiralothelphusa gibberosa n. sp. can also be differentiated from the above species by the long twisted portion of the G1, two-third length of the non-twisted portion ( Figs. 4 A, B) in contrast to the short twisted portion of the G1, half-length of non-twisted portion (Ng 1994: figs. 1B, C for S. fernandoi ; Ng & Tay 2001: figs. 27A, B for S. senex , figs. 29F, H for S. fernandoi , figs. 31A, B for S. hydrodroma ).

Figures

FIGURE 2. Spiralothelphusa gibberosa n. sp., holotype male (ZSI, WRC-C. 1186). A, dorsal view; B, frontal view; C, ventral view. Scale bar = 10 mm.

FIGURE 3. Spiralothelphusa gibberosa n. sp., holotype male (ZSI, WRC-C. 1186). A, dorsal view; B, frontal view; C, anterior male thoracic sternites; D, male abdomen; E, left third maxilliped. Scale bar = 5 mm.

FIGURE 4. Spiralothelphusa gibberosa n. sp., holotype male (ZSI, WRC-C. 1186). A, dorsal view of left G 1; B, ventral view of left G 1; C, lateral view of left G 1; D, left G 2. Scale bar = 1 mm.

FIGURE 5. Habitat of Spiralothelphusa gibberosa n. sp. A, rice fields; B, canal; C, burrow in canal embankment.