Nepinnotheres fulvia, 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 : 343-346

Nepinnotheres fulvia sp. nov.

( Figs. 6 , 7 )

Type material. HOLOTYPE: ZRC 2018.1391 , male (cl 2.8 mm, cw 2.9 mm), west of Tabad Island , Papua New Guinea, 5°08.26002’S, 145°48.71976’E, 10 m, from Fulvia australis (G.B. Sowerby II, 1834) ( Cardiidae ), PAPUA NIUGINI stn PR198, coll. A. Anker, 7 Dec 2012 . PARATYPE: ZRC 2018.1392 , female (cl 3.0 mm, cw 3.1 mm), collected together with holotype .

Description. MALE: Carapace subcircular. Front slightly produced, anterior margin weakly concave in dorsal view. Dorsum smooth, glabrous. Epistome with broad, triangular interantennular septum; median buccal margin with narrow, acute, median point. Antennular sinus of similar size to orbit; antennules folded obliquely. Antennal articles 1 and 2 fused to epistome. Eyes visible in dorsal view, filling orbit, cornea pigmented.

Maxilliped 3 ischiomerus length about twice width; inner distal margin with prominent, obtuse angle, margin distal and proximal to angle straight; outer margin strongly convex. Carpus shorter than propodus. Propodus spatulate, tapering in distal half, apex rounded, dorsally and distally setose, length 2.8× dactylus length. Dactylus digitiform, distally setose, inserted at propodal midlength, apex reaching to midway between insertion and end of propodus. Exopod inner margin straight, outer margin broadly convex; flagellum with 2 articles, distally setose.

Chelipeds stout, inflated, symmetrical from left to right. Dactylus and pollex crossing distally, with distinct gape. Dactylus arcuate, dorsal margin arcuate, sparsely setose; occlusal margin setose, with blunt triangular tooth proximal to midlength, concave in distal half, with rounded dentate subdistal lobe near base of simple, falcate dactylar apex. Pollex relatively straight, apex simple, with fringe of short setae on inner ventral margin extending onto proximal half of palm; occlusal margin setose, irregularly and minutely dentate, with short spinules on distal half, with low subdistal lobe occluding with corresponding dactylar lobe when fingers closed. Propodus palm dorsal margin 1.3× height, 1.2× length of dactylus; scattered dorsal setae; ventral margin weakly concave. Carpus unarmed, inner margin setose.

Pereopods 2–5 (walking legs 1–4) symmetrical from left to right, unarmed; extensor and flexor margins setose, P3 and 4 also with natatory setae; relative lengths in decreasing order: P3> P4> P2> P5. P2 basis anterior surface granulate. P3 merus 0.6× pcl. P2–5 dactyli similar, evenly arcuate, distally spiniform, P2–4 dactylus 0.6× propodus length, P5 dactylus 0.7× propodus length. Relative dactylus lengths: P2 = P3 = P4> P5.

Thoracic sternum anterior margin distinctly concave medially; sternites 1–3 fused; demarcation between sternites 2 and 3 partially indicated by transverse median groove; sterno-pleonal cavity reaching sternite ¾ suture.

Pleon slender, margins evenly converging distally; comprising 6 free somites and telson, widest at somites 2 and 3; telson wider than long, apex rounded.

Gonopod 1 elongate, slender, arcuate, dorsoventrally compressed, about 2/3 length of pleon, tapering to simple apex; margins setose, longest on outer margin. Gonopod 2 endopod simple, about ¼ length of gonopod 1; exopod short, slender, about as long as endopod. Pleopods 3–5 absent.

FEMALE: Carapace subcircular. Front not produced, anterior margin weakly concave in dorsal view. Dorsum smooth, very few, minute, scattered setae. Epistome with broad, triangular interantennular septum; median buccal margin with narrow, acute, median point. Antennular sinus of similar size to orbit; antennules folded obliquely. Antennal articles 1 and 2 fused to epistome. Eyes not visible in dorsal view, filling orbit, cornea pigmented.

Maxilliped 3 ischiomerus length about twice width; inner distal margin with prominent, obtuse angle, margin distal and proximal to angle straight; outer margin strongly convex. Carpus shorter than propodus. Propodus spatulate, tapering in distal half, apex rounded, dorsally and distally setose, length 3.2× dactylus length. Dactylus digitiform, distally setose, inserted at propodal midlength, apex reaching to midway between insertion and end of propodus. Exopod inner margin straight, outer margin sinuous; flagellum with 2 articles, distally setose.

Chelipeds symmetrical from left to right, surfaces sparsely setose. Dactylus and pollex relatively straight, crossing distally, without gape. Dactylus occlusal margin with blunt triangular tooth proximal to midlength, straight in distal half, sparsely setose, minutely denticulate. Pollex occlusal margin irregular, sparsely setose, minutely denticulate; with fringe of short setae on inner ventral margin. Propodus palm dorsal margin 1.5× height, 1.2× length of dactylus; ventral margin weakly concave. Carpus unarmed, inner margin setose.

Pereopods 2–5 (walking legs 1–4) symmetrical from left to right, unarmed, setose on flexor and extensor margins of merus, carpus, propodus, and dactylus, P3–4 also with natatory setae; relative lengths in decreasing order: P3> P4> P2> P5. P3 merus 0.5× pcl. P2 basis anterior surface granulate. Dactyli similar, evenly arcuate, distally spiniform; P2–4 dactyli 0.5× propodus length, of P5, 0.6× propodus length. Relative dactylus lengths: P3> P2 = P4> P5.

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

Pleon of paratype yet to reach full size, reaching to, or almost to, but not covering coxa of walking legs; of 6 free somites and telson.

Host. Fulvia australis (G.B. Sowerby II, 1834) ( Cardiidae ).

Etymology. Named fulvia , after the genus name of the host; used as a noun in apposition.

Remarks. Nepinnotheres fulvia sp. nov. is readily distinguished from the majority of its congeners in having the maxilliped 3 dactylus distinctly under-reaching ( Fig. 6B , 7B ) rather than reaching to, or over-reaching, the apex of the propodus. Six species, however, also have a maxilliped 3 dactylus that distinctly under-reaches the propodus: N. cardii ( Bürger, 1895) (type locality: Philippines), N. villosulus (Guérin, 1832) (type locality: Timor, Indonesia), N. glaberrimus ( Bürger, 1895) (type locality: Philippines), N. rathbunae ( Schmitt, McCain & Davidson, 1973) (type locality: Palau), N. rouxi (H. Milne Edwards, 1853) (type locality: Indian Ocean), and N. sanguinolariae ( Pillai, 1951) (type locality: India). Female N. fulvia can be distinguished from N. cardii by the absence of the proximal occlusal tooth on the cheliped pollex ( Fig. 7E ) (present in N. cardii ; Ahyong & Ng 2007a: fig. 22B; Ng et al. 2019: fig. 1, 2D), and strongly setose walking legs ( Fig. 7A , E–H) (glabrous in P. cardii except for flexor margins of propodi and dactyli; Ahyong & Ng 2007a: fig. 22A; Ng et al. 2019: fig. 1). Male N. fulvia can be separated from male N. cardii by the more slender maxilliped 3 propodus (length 3× height versus 2× height in N. cardii ; Fig. 6B , Ahyong & Ng 2007a: fig. 22F) and absence of a prominent rounded tooth on the distal one-third of the cheliped pollex occlusal margin ( Fig. 6E ) (present in N. cardii ; Ahyong & Ng 2007a: fig. 22E). Female N. fulvia can be readily separated from female N. villosulus (males presently unknown) by lacking the short tomentum that densely covers the entire external surface of the cephalothorax and pereopods, and from both sexes of N. sanguinolariae by the subcircular versus transversely ovate carapace. Nepinnotheres glaberrimus , known with certainty only from the male lectotype, differs from male N. fulvia by the position of the maxilliped 3 dactylus articulation (proximal to the midlength versus at the midlength in N. fulvia ) and the presence of two prominent proximal teeth on the occlusal margin of the cheliped pollex (absent in N. fulvia ). Nepinnotheres rouxi is known only from the type description, but, based on the maxilliped 3 of the holotype figured by H. Milne Edwards (1853: pl. 11 fig. 7), differs from N. fulvia by the comparatively narrow ischiomerus (length about 2.5× width) with a broadly rounded, weakly produced inner distal angle of the ischiomerus (versus length about twice width with distinctly angular inner distal margin in the new species). Nepinnotheres rathbunae differs from N. fulvia in a similar way to N. rouxi . Another unusual feature of both sexes of N. fulvia is the presence of a granular anterior surface of the P2 coxa ( Figs. 6J , 7J ) (although more prominent in the male than female); this feature has not been previously reported in pinnotherids, although it may have been overlooked.

The male cheliped in N. fulvia sp. nov. is conspicuous among congeners for the large gape between the fingers and the presence of a denticulate subdistal lobe on the outer occlusal surface dactylus that occludes with a low swelling on the corresponding surface of the pollex, ‘interlocking’ with the curved apices of the fingers. Of known males of Nepinnotheres , such an arrangement is otherwise known only in N. cardii ( Bürger, 1895) (type locality: Philippines), N. bidentatus ( Sakai, 1939) (type locality: Wakayama, Japan) and N. taichungae ( Sakai, 2000) (type locality: Kaomei, Taiwan).

The male of N. fulvia is mature, indicated by the strongly inflated cheliped and well developed gonopods ( Fig. 6A, E, L, M ). As in N. affinis ( Bürger, 1895) from the Philippines, the G2 exopod in N. fulvia is of similar length to the endopod ( Fig. 6M ; Ahyong et al. 2012: fig. 4B, C). The female paratype of N. fulvia is apparently a late subadult, with the pleon broad but yet to reach full size to cover the coxa of the walking legs ( Fig. 7K ). Although a late subadult, diagnostic features are already well developed by this stage in other species of Nepinnotheres , notably in the proportions of the maxilliped 3 articles and pereopodal setation, so we have little hesitation in recognising the novelty of N. fulvia .

Distribution. Presently known only from off Tabad Island, Papua New Guinea.

Figures

FIGURE 6. Nepinnotheres fulvia sp. nov., male holotype, cl 2.8 mm, cw 2.9 mm, ZRC 2018.1391. A, dorsal habitus; B, right maxilliped 3; C, anterior cephalothorax; D, anterior thoracic sternum and anterior pleon; E, right chela; F–I, right P2–5; J, right P2 proximal articles, ventral view; K, pleon; L, left G1, pleonal view; M, left G2, pleonal view. Scales: A = 1.0 mm; B, L, M = 0.25 mm; C–K = 0.5 mm.

FIGURE 7. Nepinnotheres fulvia sp. nov., female paratype, cl 3.0 mm, cw 3.1 mm, ZRC 2018.1392. A, dorsal habitus; B, right maxilliped 3; C, anterior cephalothorax; D, anterior thoracic sternum; E, right chela; F–I, right P2–5; J, right P2 proximal articles, ventral view; K, pleon. Scales: A, K = 1.0 mm; B = 0.25 mm; C–J = 0.5 mm.