Kume, Naruse & Ng, 2012

Naruse, Tohru & Ng, Peter K. L., 2012, Kume tigra, a new genus and new species of carupine swimming crab (Crustacea: Brachyura: Portunidae) from Kume Island, Ryukyu Islands, Japan *, Zootaxa 3367 (1), pp. 204-210 : 205

Kume n. gen.

Type species. Kume tigra n. gen., n. sp., by present designation.

Diagnosis. Carapace tranversely broad, with oblique granulated crest on metabranchial region. Supra- to infraorbital magins continuous, supraorbital margin without fissure. Anterolateral margin with 5 teeth. Posterior margin of epistome with wide median projection. Endostomial ridges distinct. Eyes mobile, relatively short, with thick eyestalk, well developed cornea, filling orbit. Third maxilliped rectangular, ischium slightly longer than merus, merus with distolateral angle produced, not prominently auriculiform. Male thoracic sternum relatively wide; sternites 1–3 fused, sternites 3 and 4 separated by shallow groove; sternoabdominal cavity relatively wide, sutures between thoracic sternites 4 to 8 medially interrupted, ending at inner part of lateral slope of sternal cavity; no longitudinal groove discernible; distinct press button abdominal locking mechanism rod-like, positioned near inner end of suture 4/5 on sternite 5. Vulva transversely elliptical, on middle part of sternite 6, without sternal cover or ridge. Chelipeds subequal in both sexes; anterior margin of merus without distinct tooth or spine; chela long, fingers straight in outer view, weakly curved inwards in upper view, occlusal margins lined with numerous sharp teeth. P2–P4 similar in shape; P5 shortest, with laterally compressed propodus, dactylus slightly longer than propodus, lanceolate, laterally flattened. Male abdomen relatively wide; somite 2 fused to somite 3 with median part of suture not visible; somites 3–5 completely fused, forming right-angled triangular structure with telson; telson triangular, slightly broader than long. G1 simple, cylindrical, tapering gently to subtruncate tip; G2 about half length of G1, tip bifurcated.

Etymology. This genus is named after the name of the island “ Kume ”, where the expedition “KUMEJIMA 2009” took place. Gender is masculine.

Remarks. Kume n. gen. superficially most closely resembles Pele in its very broad carapace ( Figs. 1 , 2a ; Ng, 2011: figs. 3A, 4A, 5, 7A). Kume n. gen. can be separated from Pele by the presence of an oblique granulated crest on the metabranchial region of the carapace (vs. absent in Pele ; Ng 2011: figs. 5A, B, 7A); proportionately shorter ischium and slightly auriculiform distolateral angle of the merus of the third maxilliped ( Fig. 2c ) (vs. proportionately longer ischium and non-auriculiform angle; Ng 2011: fig. 7D); unarmed anterior margin of the cheliped merus ( Fig. 2d ) (vs. armed with subdistal tooth in Pele ; Ng 2011: figs. 2C, 4A, 8A), lanceolate dactylus of P5 ( Fig. 2f ) (vs. almost straight, slightly upcurved in Pele ; Ng 2011: figs. 3A, 4A, 8B); the male has symmetrical chelae and the occlusal margins of the fingers have normal teeth ( Fig. 2d, e ) (vs. with unequal chelae and spine-like teeth along occlusal margin of pollex of minor chela in Pele ; Ng 2011: fig. 6C); rod-like press-button male abdominal locking mechanism ( Fig. 3a, b ) (vs. peg-like in Pele ; Ng 2011: fig. 7E, G); the complete absence of a longitudinal median line on the sternoabdominal cavity ( Fig. 3b ) (vs. shallow line present in Pele ; Ng 2011: fig. 7E); the relatively smaller and elliptically shaped vulva (vs. large, rounded in Pele ; Ng 2011: fig. 9); short and broad telson with a relatively broader anterior part of the sternoabdominal cavity ( Fig. 3c ) (vs. elongated, linguiform telson and relatively narrower sternoabdominal cavity; Ng 2011: fig. 8C); almost straight, simple G1 ( Fig. 3d ) (vs. G1 with a stout base and long, straight and slender distal part, sharply bent medially in Pele ; Ng 2011: figs. 6A, 8D, E); and bifurcated distal end of G2 ( Fig. 3e ) (vs. unilobed in Pele ; Ng 2011: fig. 8F).

Kume n. gen. is also similar to Libystes A. Milne-Edwards, 1867 , sensu lato, in its unarmed anterior margin of the cheliped merus ( Fig. 2d ) and the slender dactylus of P5 ( Fig. 2f ). The differences between Kume n. gen. and Libystes are: broad and elliptical shape of the carapace ( Figs. 1 , 2a ) (vs. subquadrate to subovate in Libystes ); slightly produced distolateral angle of the third maxilliped ( Fig. 2c ) (vs. prominently auriculiform in Libystes ); the absence of the longitudinal median line on the sternal cavity ( Fig. 3b ) (vs. longitudinally line present, but posterior end fused in Libystes ); and the G1 is gently curved, subcylindrical with a tapering distal part ( Fig. 3d ) (vs. very slender and sinuous or short and subtruncate in Libystes ) (see Ng 2011 for details of Libystes ).

Ng (2011) has discussed the systematic problems with Libystes and the allied genus Catoptrus A. Milne- Edwards, 1870, at length (see also Fujita & Naruse 2011), noting that Libystes will need to be separated into at least two groups in an ongoing revision of the genus by the present authors. As such, this matter will not be elaborated on here.

Figures

FIGURE 1. Colours in life. Kume tigra n. gen. et sp. a, holotype male, 2.4 × 4.7 mm, RUMF-ZC-1400; b, paratype female (2.9 × 6.1 mm), ZRC 2010.0182.

FIGURE 2. Kume tigra n. gen. et sp. Paratype female (2.9 × 6.1 mm), ZRC 2010.0182.

FIGURE 3. Kume tigra n. gen. et sp. Holotype male (2.4 × 4.7 mm), RUMF-ZC-1400.