Indopinnixa oryza, 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 : 227-229

Indopinnixa oryza n. sp.

( Figs. 4–6)

Material examined. Holotype: male, 2.6 × 4.3 mm, RUMF-ZC-1394, Inanse , Urasoe , Okinawa Island , Ryukyu Islands, Japan, coll. T. Maenosono, 5 Jul. 2009 . Paratypes: 1 male, 2.1 × 3.5 mm, RUMF-ZC-1395, 1 male, 2.0 × 3.3 mm, ZRC 2010.0179 , Sesoko Island , Ryukyu Islands, Japan, coll. T. Maenosono, 16 May 2009 ; 1 ovig. female, 2.2 × 3.8 mm, RUMF-ZC-1396, Sesoko Island , Ryukyu Islands, Japan, coll. T. Maenosono, 8 June 2009 ; 1 ovig. female, 1.8 × 3.1 mm, ZRC 2010.0180 , Sesoko Island , Ryukyu Islands, Japan, coll. T. Maenosono, 7 May 2009 .

Description. Carapace ( Fig. 4a) suboval, CW 1.62–1.77 times CL, dorsal surface slightly convex longitudinally and transversely, scattered with setae, antero- and posterolateral margins continuous, lateral margin cristate except for anterior and posterior portions. Front sloping anteroventrally, frontal margin straight. Supraorbital and infraorbital margins continuous, entire, inner orbital tooth indistinct, orbit short, fully occupied by eye ( Fig. 5a).

Epistome with median tooth on posterior margin. Antennule set transversely. Antenna with basal article posteriorly protruding beyond posterior margin of epistome, distally intruded into orbit. Eye subcircular, short, with distinct cornea. Third maxilliped ( Fig. 5b) with ischium and merus fused; palp large, palp segments in similar length, 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 quarter of ischium-merus, with long flagellum.

Chelipeds subequal, scattered with setae; chela ( Fig. 5c) moderately large, palm with outer lower surface smooth, glabrous, outer upper surface setose, fingers slightly longer than half the length of palm; immovable finger nearly straight, occlusal margin blade-like, except for pointed tip; movable finger deflexed subdistally, extensor surface granulated. Ambulatory legs fringed with short setae, P2, P3 and P5 similar in shape, P5 ( Fig. 5e) shortest, P4 ( Fig. 5d) longest and stoutest; merus of P4 relatively stout, anterodistal angle roundly expanded.

Sternoabdominal cavity deep, continuous to buccal cavern. Margin of sternoabdominal cavity with one button on thoracic sternites 4 and 5 each, with longitudinal ridge along sternites 6 to 7, buttons and distal end of ridges corresponding to lateral end of sutures of abdominal somites or telson, forming locking mechanism. Penis sternal.

Male abdomen ( Fig. 6a) with first somite concealed under posterior margin of carapace; third somite convex laterally; fourth to sixth somites externally demarcated by shallow grooves but functionally fused, lateral margins of each somite concave, fourth and fifth somites with bud-like pleopods; telson distally rounded, longer than sixth somite, slightly wider than sixth somite. G1 ( Fig. 6b, c) gently arching, apical process beak-like, process directed outwards. G2 ( Fig. 6d) small.

Etymology. The species name “oryza” (= rice) alludes to the shape of the carapace of the new species. The name is used as noun in apposition.

Ecological note. Specimens of Indopinnixa oryza n. sp. were collected from a subtidal (1 m) silty reduced layer under buried rock. Although sipunculan worms and peanut worms were collected from the same habitat, it remains unknown whether I. oryza n. sp. is commensal with these worms.

Remarks. Indopinnixa oryza n. sp. can be differentiated from I. sipunculana and I. mortoni by its beak-like and outwardly directed apical process of the G1 ( Fig. 6b, c) and functionally fused fourth to sixth abdominal somites of male ( Fig. 6a) ( Rahayu & Ng 2010: figs. 3A–C, 6A–E). In addition, the anterolateral margin of I. oryza n. sp. is nearly entire, with very slight notch ( Fig. 4a), whereas I. sipunculana and I. mortoni possess a distinct notch ( Manning & Morton 1987: fig. 1A; Davie 1992: fig. 1C).

Indopinnixa oryza n. sp. is morphologically similar to some Pinnixa species , such as P. leptosynaptae Wass, 1968 , from Florida, and P. darwini Garth, 1960 , from Galapagos Islands, in their relatively narrow carapace, fused fourth to sixth abdominal somites of male, and proportionally similar lengths of pereiopods ( Wass 1968: figs. 1, 2; Garth 1960: fig. 1A, E). Indopinnixa oryza n. sp., however, can be differentiated from P. leptosynaptae by the smooth dorsal surface of the carapace ( Fig. 4a) (vs. having four transverse ridges in P. leptosynaptae ; Wass 1968: fig. 1), the beak-like apical process of the G1 ( Fig. 6b, c) (vs. without differentiated tip in P. leptosynaptae ; Wass 1968: fig. 6), the presence of sutures on the outer sides of fused abdominal somites ( Fig. 6a) (vs. without sutures on the outer sides of fused abdominal somites in P. leptosynaptae ; Wass 1968: fig. 2), and prominently projected lobe of the subdistal portion of the anterior margin of P4 merus ( Fig. 5d) (vs. not prominently projected in P. leptosynaptae ; Wass 1968: fig. 1). In addition, I. oryza n. sp. can be differentiated from P. darwini by the rounded telson ( Fig. 6a) (vs. triangular in P. darwini ; Garth 1960: fig. 1E) and prominently projected lobe of the subdistal portion of the anterior margin of P4 merus ( Fig. 5d) (vs. not prominently projected in P. darwin ; Garth 1960: fig. 1A).