Indopinnixa kumejima, Naruse & Maenosono, 2012

Naruse, Tohru & Maenosono, Tadafumi, 2012, Two new species of Indopinnixa Manning & Morton, 1987 (Decapoda: Brachyura: Pinnotheridae) from the Ryukyu Islands, Japan *, Zootaxa 3367, pp. 222-231 : 223-227

Indopinnixa kumejima n. sp.

( Figs. 1–3)

Material examined. Holotype: male, 2.7 × 6.5 mm, RUMF-ZC-1397, off Shimajiri , Kume Island , Ryukyu Islands, Japan, KUMEJIMA 2009 stn. Dredge 69, 26°19.054´N 126°48.702´E – 26°18.958´N 126°48.724´E, 5.6–13.1 m, mud, coll. KUMEJIMA 2009, 18 Nov. 2009 . Paratypes: 1 male, 2.4 × 5.6 mm, ZRC 2010.0181 , 1 male, 1.8 × 4.0 mm, RUMF-ZC-1398, same data as holotype .

Description. Carapace ( Figs. 1a, 2a) elliptical, CW 2.30–2.39 times CL, dorsal surface concave at gastric region and along posterolateral margin of mesobranchial region, with one transverse ridge on cardiac region, leaving some distance from posterolateral margin, anterolateral margin inserted onto carapace toward postorbital region, junction between antero- and posterolateral margins produced laterally, placed just anterior to base of P4. Front narrow, slightly wider than orbit, frontal margin straight. Supraorbital and infraorbital margins continuous, entire; inner orbital tooth indistinct.

Epistome with median triangular projection on posterior margin. Antennule set transversely. Antenna distally intruded into orbit. Eye subcircular, short, with distinct cornea. Third maxilliped ( Fig. 2b) with ischium and merus fused; palp large, propodus and dactylus tongue-shaped, dactylus attached to subproximal part of lateral margin of propodus; mesial margin of dactylus and distal margins of propodus and carpus with long setae; exopod simple, reaching distal end of ischium-merus, with long flagellum.

Chelipeds ( Fig. 1a) relatively large, subequal. Merus with lower and upper margins setose, lower inner margin dilated, lamellar, lower surface concave, chela partially fit in concave part when folded. Carpus with distal margin setose. Chela ( Figs. 1b, 2c) relatively large, rather compressed laterally, proximal part of inner surface setose, palm with outer lower surface smooth, glabrous, with 2 longitudinal rows of setae on middle and near upper margin of outer surface; upper surface sparsely granulated. Fingers about half-length of palm, extensor and occlusal margins setose; immovable finger with 3 basally-fused teeth subdistally, movable finger with 1 triangular tooth medially and few smaller teeth. Ambulatory legs fringed with short setae, P2, P3 similar in shape, P4 ( Figs. 1a, 2d) longest, stoutest, P5 ( Figs. 1a, 2e) shortest; merus of P4, P5 with dense mat of setae on posterior margin, P4 with both upper and lower margins of posterior surfaces of meri and both upper and lower margins of inner surface of propodi lined with granules, hollowed between margins.

Sternoabdominal cavity deep, continuous to buccal cavern. Margin of sternoabdominal cavity with buttons on posterior angle of thoracic sternites 4 and angle between sternites 6 and 7, buttons corresponding to lateral concavities of sixth and fourth abdominal somites when abdomen closed, forming locking mechanism. Penis sternal.

Male abdomen ( Fig. 3a) with first somite partially concealed under posterior margin of carapace; third somite convergent distally; third to sixth somites externally demarcated by shallow grooves but functionally fused, lateral margins of fourth and sixth somites concave; telson as wide as third somite, distally rounded, longer than sixth somite, distal margin weakly concave medially. G1 ( Fig. 3b, c) gradually curved outwards, distal tip scoop-like, with concave surface on mesial side. G2 (fig. 3d) small.

Etymology. The new species is named after Kumejima (= Kume Island), the type locality of the species. The name is used as noun in apposition.

Ecological note. Speicmens of Indopinnixa kumejima n. sp. were collected by dredging at a depth of 5.6 – 13.1 m with a muddy substratum.

Remarks. Indopinnixa kumejima n. sp. can be distinguished from I. sipunculana Manning & Morton, 1987 , and I. mortoni Davie, 1992 , by the presence of a transverse ridge on intestinal region of the carapace ( Fig. 2a). Moreover, I. kumejima n. sp. has a proportionately much wider carapace (CW 2.30–2.39 times CL) (vs. 1.83 (male) to 2.15 (female) times in I. sipunculana ; 1.75 times in I. mortoni ) ( Davie 1992; Manning & Morton 1987). Rahayu & Ng (2010) described two Indopinnixa species from Lombok, Indonesia, both of which have a transverse ridge on the intestinal region of the carapace. Indopinnixa kumejima n. sp., however, can be differentiated by its relatively wider carapace (CW 2.30–2.39 times CL) (vs. 1.92 (male) and 2.0 (female) times in I. kasijani ; 1.83–2.00 times in I. moosai ) ( Rahayu & Ng 2010). The shape of the G1 is also diagnostic. The G1 of I. kumejima n. sp. is gently curving outwards, with spoon-shaped apical process, concave surface on mesial side ( Fig. 3d, c). The apical process of I. kasijani is sinuous, while that of I. moosai is almost straight with rounded distal tip ( Rahayu & Ng 2010: figs. 3A, B, 6A–D).

Pinnixa pembertoni Glassell, 1935 , and P. penultipedalis Stimpson, 1858 , are perhaps close to I. kumejima n. sp. Pinnixa pembertoni was described based on a single male specimen from Baja California. The fusion of male fourth to sixth abdominal somites links this species to Indopinnixa . However, the disjunct distribution of P. pembertoni from western Pacific Indopinnixa spp. , and the lack of a figure or photograph makes it difficult to determine its generic position. Indopinnixa kumejima n. sp. can be still separated from P. pembertoni by the relatively broader carapace (CW 2.30–2.39 times CL in the new species vs. about two times in P. pembertoni ) and the condition of the fusion of the male abdominal somites (third to sixth somites are functionally fused in the new species vs. fourth to sixth somites are fused in P. pembertoni ) ( Figs. 1a, 2a, 3a; Glassell 1935: 102). Pinnixa penultipedalis was described by a single female specimen from Hong Kong. Since the key character of Indopinnixa is the fusion of male abdominal somite, it is again impossible to clarify its generic position. The new species differs from P. penultipedalis in the proportionally wider carapace (CW 2.30–2.39 of CL vs. 2.11 in P. penultipedalis ), cardiac ridge not reaching lateral margin of the carapace rather than spanning the whole breadth in P. penultipedalis ), and the proportionally narrower P4, with merus about half as broad as long (vs. four-fifths as broad as long in P. penultipedalis ) ( Figs. 1a, 2a, d; Stimpson 1858: 54; 1907: 143).

An opportunity is taken here to comment on the taxonomy of P. penultipedalis . Manning & Morton (1987) pointed out that P. penultipedalis sensu Shen (1937) is not P. penultipedalis s. s., because “Shen’s species, which probably is undescribed, differs from P. penultipedalis … in lacking a distinct ridge across the posterior part of the carapace” ( Manning & Morton 1987: 545). Other than the transverse ridge of the carapace, the most characteristic feature of P. penultipedalis is the very wide merus of P4, which is about four-fifth as wide as long (Stimpson 1858; 1907). Although several authors have recorded “ P. penultipedalis ” from Japan (Nagasaki: Ortmann 1904; Harimanada, eastern Seto Inland Sea: Watanabe & Tanida 2001; Oki Island, Sea of Japan: Yamauchi & Konishi 2005), China (Tsangkou, Shan Dong Province: Shen 1937), and even from Mozambique (Inhambane: Barnard 1955), it is probable that none of these records are P. penultipedalis s. s. The specimens recorded by Shen (1937), Watanabe & Tanida (2001) and Yamauchi & Konishi (2005) possess a transverse ridge only on the cardiac region, instead of a distinct ridge that spans the whole width of the posterior part of the carapace. The specimens recorded by Ortmann (1904) and Barnard (1955) may have such a complete ridge on the carapace, but the carapace is too narrow (CW 1.95 times CL in Ortmann 1904; 1.86 times in Barnard, 1955) when compared with P. penultipedalis . Sakai (1976) had already doubted the identity of Ortmann’s (1904) specimen of P. penultipedalis without further comment. Even among these non- P. penultipedalis specimens, there are species-level differences. For example, although Shen’s (1937) specimen possesses tubercles on the upper surfaces of the cheliped palm and movable fingers, such tubercles are not described for the specimens of Yamauchi & Konishi (2005). This suggests that the specimens previously identified as P. penultipedalis may actually belong to several undescribed species. Their taxonomy will need to be revised in the future. In any case, all these taxa differ from I. kumejima n. sp.