Rayapinus maenosonoi, Rahayu & Ng, 2014

Rahayu, Dwi Listyo & Ng, Peter K. L., 2014, New genera and new species of Hexapodidae (Crustacea, Brachyura) from the Indo-West Pacific and east Atlantic, Raffles Bulletin of Zoology 62, pp. 396-483 : 460-462

Rayapinus maenosonoi , new species

( Figs. 2D , 52 , 53 )

Material examined. Holotype: male (6.6 × 4.6 mm) (RUMF- ZC-2115), Sesoko Island near Okinawa Island, Ryukyu Islands , Japan, coll. T. Maenosono, 11 May 2010 . Paratype: Japan: 1 female (4.3 × 3.1 mm) ( ZRC 2012.1034 ), same locality as holotype, coll. T. Maenosono, 8 June 2009 .

Diagnosis. Carapace subquadrate, about 1.4 times as broad as long, dorsal surface smooth; regions indistinct; anterolateral margin arcuate; posterolateral corner with angled prominence over base of posterior pereopods; orbit distinct, transverse; eye small; pterygostomial region with row of striae. Third maxillipeds relatively broad, tuberculate; ischium longer than merus, with rounded mesial margin; merus broader than long; exopod relatively narrow, flagellum well developed. Chelipeds stout, unequal; major chela with slight gap when fingers closed; minor chela with relatively wider gap between fingers. P2–P4 short, stout, P3 longest; merus of P4 2 times as long as broad. Male thoracic sternum broad; sternoabdominal cavity not reaching base of sternite 3; thoracic sternal groove short, extends obliquely from sternoabdominal cavity. Male abdomen relatively narrow; somites 1 and 2 free; somites 3–5 fused, lateral margin sinuous; somite 6 distinctly shorter than length of somites 3–5, lateral margin with blunt triangular expansion medially; telson short with distal margin rounded, setose. G1 stout, bent subdistally, apices wide, not concealed under abdomen. Female abdomen narrow, somites 1–6 fused, suture visible between somites 5 and 6 but functionally fused; lateral margin of somite 6 expanded subproximally, telson almost as long as somite 6, distal margin rounded.

Description. Carapace subquadrate, about 1.4 times as broad as long, dorsal surface smooth; regions indistinct, median U-shaped depression shallow; some granules present on dorsolateral margins, only scattered granules on posterior margin ( Fig. 52A ). Anterolateral margin arcuate; posterolateral corner with angled prominence over base of posterior pereopods ( Figs. 52A , 53A ). Orbit distinct, transverse; eye small, slightly movable, cornea black, wider than tuberculate peduncle ( Fig. 53B ). Pterygostomial region with row of oblique striae, oblique row of setae under row of striae, adjacent to Milne Edwards’ opening ( Fig. 53B ). Third maxillipeds relatively broad, tuberculate, without gap between them ( Figs. 52B , 53E ); ischium longer than merus, with rounded mesial margin; merus broader than long; carpus, propodus and dactylus cylindrical; dactylus longer than propodus, combined length of dactylus, propodus and carpus shorter than that of merus and ischium; exopod narrow, 0.4 width of ischium, flagellum well developed.

Chelipeds stout, unequal ( Fig. 52D ). Major chela ( Fig. 53G ) with slight gap when fingers closed; large teeth present at cutting edge of dactylus; dactylus with longitudinal groove on outer surface, tufts of setae on cutting edge proximally; inner surface near upper margin with longitudinal ridge; palm slightly wider than long, surface with sparse tubercles on outer surface, shallow longitudinal groove on outer surface of fixed finger; carpus without setae dorsally, row of tubercles and setae dorsomesially; merus short, few tubercles and fringe of setae dorsomesially. Minor chela ( Fig. 53H ) with relatively wider gap between closed fingers; dactylus with longitudinal groove on outer surface; inner surface with longitudinal ridge near upper margin; outer surface of palm covered by large tubercles, carpus and merus unarmed, fringe of setae on each dorsomesial margin. P2–P4 short, stout ( Fig. 52A ); P3 longest; P2 most slender, dactylus upcurved, few tubercles on upper margin, fringe of short setae on upper and lower margins, slightly shorter than propodus, latter with row of tubercles on upper and lower margins distally accompanied by setae, carpus longer than propodus, tubercles on outer upper half, tufts of setae distally, merus about 1.7 times length of carpus, upper and lower margins with row of tubercles and tufts of short setae. P3 stouter, longer than P2; P4 ( Fig. 53I ) stouter than P3; ornamentation and setation as on P2; merus of P4 2 times as long as broad.

Male thoracic sternum broad ( Figs. 52B , 53C, D ), sternites 1 and 2 fused, separated from sternite 3 by distinct ridge; sternite 3 separated laterally from sternite 4, medially appear fused, sternites 4–7 well developed, separated by distinct sutures; thoracic sternal groove short, extends obliquely from sternoabdominal cavity, reaching middle of sternite 4 ( Figs. 52B , 53D ); sternite 8 exposed, triangular, as long as abdominal somite 1; sternoabdominal cavity not reaching middle of sternite 4. Male abdomen relatively narrow ( Figs. 52B , 53F ); somites 1 and 2 free; somites 3–5 fused, lateral margin sinuous; somite 6 distinctly shorter than length of somites 3–5, lateral margin forming blunt triangular expansion medially; telson short, with rounded, setose margin.

G1 ( Fig. 53J, K ) bent subdistally, directed anterolaterally, distal part slightly tapered, tip rounded with several spines, mesial and lateral margin with sparse long setae, apices not concealed under abdomen, exposed on thoracic sternal groove, obscured by setae of telson. Female abdomen narrow ( Fig. 53L ), with somites 1–6 fused, somites 1–5 with very shallow, indiscernible sutures, suture visible between somite 5 and 6 but functionally fused; somite 6 distinctly shorter than somites 3–5, lateral margin expanded subproximally, telson almost as long as somite 6, distal margin rounded.

Colour. In life, carapace yellow or light yellow, merus and carpus of chelipeds and P2–P4 yellow, propodus and dactylus white yellowish ( Fig. 2D ).

Etymology. Named after Tadafumi Maenosono who collected the type specimens.

Remarks. As mentioned earlier, Rayapinus , new genus, is similar to Hexapinus in the extent of the male thoracic sternal groove. However, Rayapinus maenosonoi can be easily separated from Hexapinus latipes and H. simplex by having proportionately much shorter and stouter P2–P4 with a very short dactylus, and a G 1 in which the distal part is expanded.

Type locality. Sesoko Island near Okinawa Island, Ryukyu Islands, Japan ,

Distribution. Okinawa Island, Ryukyu Islands, Japan. Subtidal, 1.5– 2 m.

Figures

Fig. 2. Colours in life. A, Mariaplax ourabay, new species, holotype male (7.6 × 5.4 mm) (RUMF-ZC-2114), Oura Bay, Okinawa Island, Japan; B, Mariaplax ourabay, new species, paratype female (9.2 × 7.0 mm) (ZRC 2012.1032), Oura Bay, Okinawa Island, Japan; C, Mariaplax narusei, new species, holotype male (9.6 × 5.8 mm) (RUMF-ZC-2112), Funaura Bay, Iriomote Island, Japan; D, Rayapinus maenosonoi, new species, holotype male (6.6 × 4.9 mm) (RUMF-ZC-2115) Sesoko, Okinawa, Japan; E, Hexaplax megalops Doflein, 1904, male, (13.5 × 9.0 mm) (MNHN-IU-2011-1026), west of New Hanover; F, Hexaplax aurantium, new species, paratype male (12.1 × 8.4 mm) (MNHN-IU-2011-1527), south of Lae, Gulf of Huon; G, Hexaplax saudade, new species, paratype male (16.9 × 9.8 mm) (ZRC 2013.1692), AURORA, 2007, station CP2658, Philippines; H, Hexaplax saudade, new species, male (15.9 × 11.1 mm) (ZRC 2008.1456), Su-Ao fish port, Ilan province, Taiwan.

Fig. 52. Rayapinus maenosonoi, new species, holotype male (6.6 × 4.9 mm) (RUMF-ZC-2115). A, overall view of carapace, chelipeds and P2–P4; B, ventral view of cephalothorax; C, frontal view of cephalothorax; D, chelae.

Fig. 53. Rayapinus maenosonoi, new species. A–K, holotype male (6.6 × 4.9 mm) (RUMF-ZC-2115); L, paratype female (4.3 × 3.1 mm) (ZRC 2012.1034). A, carapace; B, anterior view of carapace; C, thoracic sternites 1–5, showing sternoabdominal cavity and thoracic sternal groove; D, thoracic sternites 1–5, showing thoracic sternal groove and telson; E, left third maxilliped; F, male abdomen and telson, G, major chela; H, minor chela; I, left P4; J, K, G1; L, female abdomen and telson. Setae on chelae not drawn. Scale bars = 1.0 mm.