Buergeres choprai, Ahyong & Ng, 2020

Ahyong, Shane T. & Ng, Peter K. L., 2020, New species of pinnotherid crabs from Southeast Asia and Papua New Guinea (Crustacea: Decapoda: Brachyura), Zootaxa 4816 (3), pp. 333-349 : 338-340

Buergeres choprai sp. nov.

( Figs. 3 , 4 )

Type material. HOLOTYPE: MNHN IU-2013-1307 , spent female (cl 3.6 mm, cw 4.0 mm), west of Tab Island , Papua New Guinea, 1–17 m, from Holothuria (Actinopyga) echinites , PAPUA NIUGINI PR118 , 28 November 2012.

Description. FEMALE: Carapace rounded-subquadrate, high, vaulted, slightly wider than long, widest near midlength. Front weakly produced, anterior margin weakly concave in dorsal view. Anterolateral margins poorly defined. Dorsum smooth, glabrous, outline of cardiac region weakly indicated by faint, shallow groove; anterior median groove absent; dorsal midline convex in profile. Epistome with narrow triangular interantennular septum; median buccal margin with acute, triangular median point. Antennular sinus of slightly larger than orbit; antennules folded slightly obliquely. Antennal articles 1 and 2 fused to epistome. Eyes partially visible in dorsal view, filling orbit, cornea pigmented.

Maxilliped 3 ischiomerus length 1.7× width; inner proximal margin convex; inner margin with blunt, obtuse angle slightly distal to midlength, margin on either side weakly concave; outer margin strongly convex. Carpus half propodus length. Propodus spatulate, gently tapering in distal half, apex rounded, dorsally and distally setose, length less than twice dactylus length. Dactylus sub-clavate, widest distal to midlength, apex rounded, distally setose, inserted slightly proximal to propodal midlength, apex almost reaching end of propodus. Exopod inner margin straight, outer margin convex; flagellum with 2 articles, distally setose.

Chelipeds symmetrical from left to right. Dactylus and pollex relatively straight, crossing distally, without gape. Dactylus dorsal margin convex, smooth, proximally setose; occlusal margin with blunt triangular tooth proximal to midlength, gently sinuous margin in distal half, sparsely setose, minutely denticulate. Pollex occlusal margin with blunt triangular tooth and 2 rounded lobes proximally, remaining margin crenulate, gently curved, sparsely setose, minutely denticulate along distal half; with fringe of setae on inner ventral margin extending onto inner palm surface. Propodus palm outer surface smooth, glabrous; dorsomesial surface with scattered setae proximally; dorsal margin 1.4× height, 1.1× length of dactylus; ventral margin sinuous. Carpus unarmed, inner margin setose.

Pereopods 2–5 (walking legs 1–4) symmetrical from left to right, unarmed; relative lengths in decreasing order: P2 = P3> P4> P5. P3 merus length 0.4× pcl. P2–4 similar; merus extensor margin broadly convex, extensor and flexor margins setose proximally; carpus glabrous; dactylus and propodus flexor margins setose; dactyli subequal, stout, falcate, evenly arcuate, distally spiniform, length 0.4× propodus length; basis anterior surface smooth, not granulate. P5 merus tapering distally, distinctly shorter than P2–4 merus, extensor and flexor margins margins straight, setose; propodus margins parallel, flexor margin setose; dactylus slender, weakly curved, almost straight, flexor margin setose but unarmed, 0.8× propodus, twice length of P2–4 dactyli.

Thoracic sternum anterior margin shallowly biconcave medially; sternites 1–3 indistinguishably fused.

Pleon of 6 free somites and telson, extending to buccal region, covering bases of walking legs.

Host. Holothuria (Actinopyga) echinites (Jaeger, 1833) (Holothuriidae) .

Etymology. Name for B. Chopra, who discovered the B. deccanensis and for his major contributions to Indian Ocean carcinology.

Remarks. Buergeres choprai sp. nov. is the fourth recognised species of the genus, alongside B. ortmanni ( Bürger, 1895) (type species) ( Singapore and the Philippines), B. deccanensis (Chopra, 1931) (eastern India) and B. holothuriae (Semper, 1880) ( Philippines) . The new species is readily separated from B. holothuriae by the glabrous rather than tomentose outer surface of the cheliped palm of B. holothuriae and more subquadrate versus subcircular carapace outline. Buergeres choprai can be separated from P. ortmanni by the proportionally shorter P5 dactylus (about twice versus triple length of the P2 dactylus) and the setation of the P2–4 meral extensor margins (sparely setose on the proximal half versus densely setose for at least three-fourths of the length in P. ortmanni ) (cf. Ng & Manning 2003). In carapace shape and pereopodal features, Buergeres choprai most closely resembles B. deccanensis . Comparison with Chopra’s (1931) excellent figures and account shows that B. choprai differs from B. deccanensis in having proportionally shorter P5 dactyli (distinctly shorter than the propodus extensor margin in B. choprai versus as long as extensor margin in B. deccanensis ), the setose rather than glabrous dorsal proximal margin of the cheliped dactylus, and P2–5 meral setation (extensor margin setose in B. choprai , glabrous in B. deccanensis ; Chopra 1931: pl. 7 fig 4). Chopra (1931) also emphasised the presence of distinct grooves around the cardiac region and along the anterior midline as characteristic of B. deccanensis ; in B. choprai the cardiac region is at most weakly demarcated and no median groove is evident. Well-marked carapace regions are uncommon in Pinnotheridae and Buergeres , and apparently unique to B. deccanensis . Males of B. choprai are currently not known.

Distribution. Presently known only from the type locality.

Figures

FIGURE 3. Buergeres choprai sp. nov., spent female holotype, cl 3.6 mm, cw 4.0 mm, MNHN IU-2013-1307: A, dorsal habitus; B, right maxilliped 3; C, anterior cephalothorax; D, anterior thoracic sternum; E, right chela; F–I, right P2–5. Scales: A = 2.0 mm; B = 0.5 mm; C–I = 1.0 mm.

FIGURE 4. Buergeres choprai sp. nov., spent female holotype, cl 3.6 mm, cw 4.0 mm, MNHN IU-2013-1307: dorsal habitus. Photo: T.-Y. Chan.