Mariaplax ourabay, 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 : 446-449

Mariaplax ourabay , new species

( Figs. 2A, B , 41 , 42 )

Material examined. Holotype: male (7.6 × 5.4 mm) (RUMF- ZC-2114), Futami, Oura Bay, Okinawa Island , Ryukyu Islands ,

Japan, coll. Oura Bay Survey Team, 20 June 2009. Paratype : Japan: 1 ovigerous female (9.2 × 7.0 mm) ( ZRC 2012.1032 ), same locality as holotype, 22 June 2009

Diagnosis. Carapace subquadrate, about 1.4 times as broad as long, dorsal surface granulated; regions indistinct, H-shaped depression shallow medially ( Fig. 41A ). Eye small, slightly movable, cornea small, globular, narrower than peduncle, peduncle with scattered granules. Pterygostomial region with row of oblique striae and scattered tubercles. Third maxilliped ( Figs. 41B , 42D ) broad, ischium longer than merus, mesial margin straight; 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 ( Fig. 41D ) stout, unequal; major chela with slight gap when fingers closed, palm slightly wider than long, surface covered with tubercles; minor chela with narrow gap when fingers closed, dorsal surface of palm covered by large tubercles. P2–P4 relatively long ( Fig. 41A ); merus of P4 2.8 times as long as broad, shallow longitudinal median groove present; P2 with dactylus upcurved. Male thoracic sternum broad ( Figs. 41B, C , 42B, C ); sternites 1 and 2 fused, separated from sternite 3 by distinct ridge; sternites 3 and 4 fused; thoracic sternal groove short, extends obliquely from sternoabdominal cavity to middle of sternite 3 ( Figs. 41B , 42B ); sternite 8 exposed, rectangular, slightly longer than abdominal somite 1; sternoabdominal cavity reaches base of sternite 3. Male abdomen ( Figs. 41C , 42E ) relatively narrow; somites 1 and 2 free, somites 3–5 fused, lateral margin sinuous; somite 6 slightly shorter than length of somites 3–5, lateral margin expanded medially into blunt triangular projection; telson almost as long as somite 6, distal margin rounded, margin setose. G1 ( Fig. 42F, G ) slender, slightly S-shaped, sparse short setae on mesial and lateral margins; distal part tapered, not concealed under abdomen, exposed on thoracic sternal groove, obscured by setae of telson. Female abdomen relatively narrow, with 6 free somites and telson ( Fig. 42H ).

Colour. In life, carapace mottled pink and cream, with the branchial region darker pink, pereopods cream ( Fig. 2A ). Female lighter coloured than male ( Fig. 2B )

Etymology. Named after the type locality Oura Bay, Okinawa Islands, Japan. The name is used as a noun in apposition.

Remarks. The male telson of Mariaplax ourabay , new species, is almost as long as the sixth abdominal somite, a characters shared only with M. granulifera . However, the male abdomen of these two species differs in the length proportion of the somite 6 to that of the somites 3–5 (0.6 in M. ourabay versus 0.8 in M. granulifera ). Furthermore, the G1 structures of these two species differ markedly: M. ourabay has long, slender G1 with a pointed tip ( Fig. 42F, G ) while in M. granulifera , the G1 is stout and proximally much wider than the tip ( Fig. 36I, J ).

Type locality. Futami , Oura Bay , Okinawa Island, Ryukyu Islands, Japan .

Distribution. Oura Bay, Okinawa Island, Ryukyu Islands, Japan. Intertidal.

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. 41. Mariaplax ourabay, new species, holotype male (7.6 × 5.4 mm) (RUMF-ZC-2114). A, overall view of carapace, chelipeds and P2–P4; B, ventral view of cephalothorax; C, abdomen and telson; D, chelae.

Fig. 42. Mariaplax ourabay, new species, holotype male (7.6 × 5.4 mm) (RUMF-ZC-2114). A, dorsolateral margin of carapace; B, thoracic sternites 1–5, showing sternoabdominal cavity and thoracic sternal groove; C, thoracic sternites 1–5, showing thoracic sternal groove and telson; D, left third maxilliped; E, male abdomen and telson; F, G, G1; H, female abdomen and telson. Scale bars = 1.0 mm.

Fig. 36. Mariaplax granulifera (Campbell &Stephenson, 1970), male (6.2 × 4.5 mm) (QM-W8299). A, dorsolateral margin of carapace; B, thoracic sternites 1–5, showing sternoabdominal cavity and thoracic sternal groove; C, thoracic sternites 1–5, showing thoracic sternal groove and telson; D, male abdomen and telson; E, left third maxilliped; F, major chela; G, minor chela; H, left P4; I, J, G1. Scale bars = 1.0 mm