Petalomera indica Alcock, 1900

Patel, Heris, Mitra, Santanu & Trivedi, Jigneshkumar, 2025, The rediscovery of Petalomera indica Alcock, 1900 (Crustacea: Brachyura: Dromiidae) from India, Zootaxa 5636 (2), pp. 395-400 : 396-399

Petalomera indica Alcock, 1900

( Figures 1 , 2 )

Petalomera granulata var. indica Alcock, 1900: 148 .

Petalomera indica Alcock, 1901: 55 , pl. 3, figs. 14, 14a.— Ihle 1913: 48, 91 (key & list).— McLay & Ng 2007: 113 , fig. 4.— Trivedi et al. 2018: 36 (list).

Not Petalomera granulata var. indica Urita, 1926: 1 [= Petalomera granulata Stimpson, 1858 ].

Material examined. Neotype (here in designated): ovigerous female (CW 15.79 mm, CL 16.27 mm) (LFSc.ZRC-291), Digha Mohona, West Bengal, India, coll. H. Patel, 20 December 2020.

Description. Carapace as long as wide, convex in both directions, not prominently domed, covered with numerous unevenly distributed, vesiculous blunt granules, especially on anterior half of carapace ( Fig. 1A, D ). All regions distinct, but not equally well defined. Cervical, branchial and branchio-cardiac grooves well marked ( Fig. 1A ). Crescent shaped branchio-cardiac grooves, with central pit, well-marked, joined by a shallow groove medially. Rostrum tridentate, dorsally grooved in mid-line, cut into 3 serrulate teeth, lateral rostral teeth large, separated by U-shaped sinus, triangular, median tooth small, on lower level. All teeth serrated.

Supraorbital margin concave from lateral rostral tooth, edge armed with 4 or 5 sharp granules increasing in size towards well-developed supraorbital tooth, this tooth projects strongly from orbital margin, directed anterolaterally ( Fig. 1B ). Supraorbital tooth, orbital margin continuing as a concave line to postorbital corner, with 7 or 8 sharp granules, followed by notch, margin ending at well-marked orbital fissure beneath postorbital corner ( Fig. 1A ). Upper border of orbit serrulate, with tooth sub-medially. Outer orbital angle pronounced, not dentiform. Straight line connects tip of lateral rostral tooth and postorbital corner, running along anterior carapace margin. Suborbital margin with granular denticle, anterolateral margin beginning at level of postorbital corner, armed with 2 granulated teeth: first directed almost anteriorly, second behind cervical groove, directed more laterally. Behind both these teeth, carapace margin granulated; with 3 teeth (including small tooth below level of suborbital margin). Posterolateral tooth absent. Posterior carapace margin slightly convex, not granulated ( Fig. 1A, C ).

First article of antennule longer than wide, sub-rectangular, second article inserted at disto-medial corner, folded laterally across distal end; article fitting tightly against rostral extension that joins inter-antennular septum. Third article longer than wide, folding posteriorly along with flagellum, concealed beneath supraorbital edge. First article of antenna (urinal article) wider than long, beak-shaped medially, not gaping. Second article much longer than wide, distal border with several small granules and well-developed bilobed exopod. Disto-medial corner produced as blunt lobe with third article inserted at an angle. Third and fourth article as long as wide. All antennal articles freely moveable ( Fig.1B ).

Third maxillipeds operculiform, surface with scattered coarse granules, palp exposed, margins of basis notmeeting in midline; crista dentata with 9 well-developed subacute teeth on ischium and 7 or 8 calcareous teeth on outer margin of basis.

Chelipeds subequal, more massive than ambulatory legs, with petaloid meri ( Fig. 1B ). Merus trigonal in cross-section, lower margin granulated, inner surface petaloid, nacreous, fitting closely against subhepatic area of carapace. Outer surface of carpus convex, granulated, with 2 strong distal granules, inner margin of upper border with 5 or 6 granules. Outer face of propodus with granules arranged in longitudinal rows ( Fig. 2D ). Inner margin of upper border cristate, granulated. Fingers short, down-curved, hollowed out internally, with teeth on ventral margin. Cutting edges of fingers armed with 6 or 7 well developed, distinct teeth, increasing in size distally ( Fig. 2D ).

P2 and P3 shorter than chelipeds, legs densely setose, merus of P2 petaloid, merus of P3 not petaloid, upper border sharp, cristate ( Fig. 2A, B ). Inner border of carpus and upper border of propodus prominent, granular, as are upper and outer surfaces of joints; 2 sharp tubercles present on distal end of outer surface of propodus. Dactyli as long as propodi, tips curved, inner margins armed with 4 or 5 short spines, all of similar size ( Fig. 2C ). P2 and P3 with few small granules. P4 and P5 slender, densely setose, reduced, third pair smallest, only last pair subdorsal in position. Dactylus of P5 ending in small claw-like dactylus opposable to strong propodal spine, with another distinctly shorter spine on outer propodal margin at base of dactylus ( Fig. 2F, G ). Ratio of length along dorsal margin (not including spine) to width of propodus for third and fourth legs, 1.9 and 1.3, respectively. P5 slightly longer than penultimate pair ( Fig. 1A ).

Pleon with 6 free somites, fourth or fifth segments widest, surface sparsely covered with granules. Last somite has many fewer granules than others. Telson much wider than long, tip broadly rounded. Uropod plates well developed, visible externally, used to lock pleon by fitting in front of prominent granulated flanges on coxae of P2, flanges present but do not appear to be functional ( Fig. 2E ). Spermathecal openings at end of sternal sutures 7/8, between bases of P2; openings on elevations lying close to gonopores on coxae of P3, diameter about half that of gonopores ( Fig. 2H ).

Remarks. The specimen examined in the present study from West Bengal agrees well with the description and figures of P. indica by Alcock (1900, 1901). Of the four species of Petalomera , P. pulchra and P. longipes belong to one group in which the carapace margin behind the lateral rostral teeth is eave-like, i.e. lateral rostral teeth is projected outward and create an overhang, and the merus of the P3 leg is also petaloid ( McLay & Ng 2007). Petalomera granulata and P. indica , on the other hand, do have the margin behind the lateral rostral teeth expanded, i.e. lateral rostral teeth are enlarged, and the merus of the P3 leg is flattened but not petaloid in form ( McLay & Ng 2007).With a fresh specimen of P. indica on hand, we can now expand on the differences between the two species observed by McLay & Ng (2007). Petalomera indica can be distinguished from P. granulata by the following characters: carapace not highly domed, surface covered with unevenly distributed vesiculous granules and the regions marked by deep grooves ( Fig. 1A, D ) (versus prominently domed, with the surface covered with large blunt granules (sometimes areolate) especially on the anterior half and the regions are not marked by deep grooves in P. granulata ; McLay & Ng 2007: fig. 1A, C); the lateral rostral teeth are separated by a U-shaped sinus ( Fig. 1B, C ) (versus V-shaped in P. granulata ; McLay & Ng 2007: figs. 1A, 3A); the dactylus of the P5 is opposable to large propodal spines ( Fig. 2F, G ) (versus opposable to small propodal spines in P. granulata ; McLay & Ng 2007: fig. 3G); and the inner margin of the dactylus of P2 and P3 has 4 or 5 spines ( Fig. 2C ) (versus 6 or 7 in P. granulata ; McLay & Ng 2007). The present study supports the hypothesis by McLay & Ng (2007) that P. indica is a valid species distinct from P. granulata .

As discussed earlier, the types of Petalomera granulata var. indica Alcock, 1900 , are lost. In view of its similarity to P. granulata Stimpson, 1858 , and to stabilise the taxonomy of Petalomera Stimpson, 1858 , following the revision of McLay & Ng (2007), we believe it is necessary to designate a neotype for the taxon. To this effect, we select the present specimen from West Bengal as the neotype of Petalomera granulata var. indica in order to fix the identity of the species.

Figures

FIGURE 1. Petalomera indica Alcock, 1900, ovigerous female, neotype (CW 15.79 mm, CL 16.27) (LFSc.ZRC-291), Digha Mohona, West Bengal, India. A, dorsal view; B, ventral view; C, detail of carapace tubercles right anterolateral area; D, frontal view. Scale bars = 2 mm.

FIGURE 2. Petalomera indica Alcock, 1900, ovigerous female, neotype (CW 15.79 mm, CL 16.27) (LFSc.ZRC-291), Digha Mohona, West Bengal, India. A, left P2; B, left P3; C, dactylus of left P2; D, outer view of right cheliped; E, pleon; F, G, propodus and dactylus of right P5, respectively; H, sternum. Scale bars = 1 mm.