Mariaplax streptophallus, 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 : 457-459

Mariaplax streptophallus , new species

( Figs. 50 , 51 )

Material examined. Holotype: male (7.5 × 5.4 mm) ( WAM C.15310), Cape Bowling Green, Queensland, Australia, coll. W. Goode, 23 November 1962.

Diagnosis. Carapace subquadrate, about 1.4 times as broad as long, dorsal surface pitted, granulated near margin; region indistinct, H-shaped depression on surface near middle shallow ( Fig. 50A ). Anterolateral margin arcuate; posterolateral margin with angled prominence over base of posterior pereopods ( Figs. 50A , 51A ). Eye small, slightly movable, cornea globular. Pterygostomial region with row of oblique striae ( Fig. 50C ). Third maxillipeds relatively broad, almost completely covering buccal cavity ( Figs. 50C , 51D ); ischium of third maxilliped longer than merus, mesial margin very slightly oblique; combined length of dactylus, propodus and carpus shorter than that of merus and ischium; exopod relatively narrow, 0.3 width of ischium, flagellum well developed. Chelipeds stout, unequal; major ( Figs. 50D , 51F ) and minor ( Figs. 50E , 51G ) chelae with gap when fingers closed; palm almost as long as wide, surface pitted. P2–P4 relatively short; merus of P4 2.8 times as long as broad, longitudinal groove medially; dactylus of P2 and P4 slightly upcurved. Male thoracic sternum broad ( Figs. 50B , 51B, C ), sternites 1 and 2 fused, separated from sternite 3 by distinct ridge; sternite 3 separated from sternite 4 by distinct ridge, thoracic sternal groove directed anteriorly, curved inwards, extends from sternoabdominal cavity to base of sternite 3 ( Figs. 50B , 51C ); sternite 8 exposed, triangular, as long as abdominal somite 1; sternoabdominal cavity not reaching base of sternite 3 ( Fig. 51B ). Male abdomen relatively narrow ( Figs. 50B , 51E ); somites 1 and 2 free; somites 3–5 fused, lateral margin slightly sinuous; somite 6 slightly shorter than length of somites3–5, lateral margin expanded medially into blunt triangular projection; distal margin of telson rounded, with sparse setae. G1 ( Fig. 51H, I ) bent submedially, twisted, directed anteriorly, distal part tapered, with row of spines mesially, sparse short setae laterally and mesially, distal quarter not concealed under abdomen, exposed on thoracic sternal groove, obscured by setae of telson. Female unknown.

Colour. Not known.

Etymology. From the Latin “strepto” for twisted, and “phallus” for penis, alluding to the twisted structure of the G1. The name is used as a noun in apposition.

Remarks. Mariaplax streptophallus , new species, differs from congeners in having a row of spinules near the tip of the G1. Mariaplax chenae , new species, M. propinqua , new species, and M. sinensis , new species, also have spines on their G1, but these are positioned along the midlength of the G1. The male thoracic sternal groove, which is directed anteriorly ( Fig. 51B, C ), resembles that of M. granulifera ( Fig. 36B, C ), but in M. streptophallus , the groove is curved inwards while in M. granulifera it is directed anteriorly. While it has a twisted G1 like M. chenae , the condition is more extreme in M. streptophallus , with the entire structure bent and twisted submedially, directed anteriorly and tapering distally ( Fig. 51H, I ). In M. chenae , only the G1 tip is twisted ( Fig. 25I, J ).

Mariaplax streptophallus resembles M. anfracta in the less granulated surface of the carapace but differs in having a proportionately wider carapace ( Fig. 50A versus Fig. 22A, C ), slightly oblique mesial margin of the ischium of the third maxilliped ( Fig. 51D versus Fig. 23D ), a relatively longer and more slender male abdomen ( Fig. 51E versus Fig. 23C ), and the male thoracic sternal groove is directed anteriorly ( Fig. 51B, C versus Fig. 23B, C ).

Type locality. Cape Bowling Green , Queensland, Australia

Distribution. Bowling Green, Queensland, Australia. Subtidal.

Figures

Fig. 50. Mariaplax streptophallus, new species, holotype male (7.5 × 5.4 mm) (WAM C.15310). A, overall view of carapace, chelipeds and P2–P4; B, ventral view of cephalothorax; C, third maxilliped; D, major chela, E, minor chela.

Fig. 51. Mariaplax streptophallus, new species, holotype male (7.5 × 5.4 mm) (WAM C.15310). 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, major chela; G, minor chela; H, I, G1. 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

Fig. 25. Mariaplax chenae, new species, A–J, holotype male (9.2 × 6.1 mm) (IOCAS); K, paratype female (8.2 × 5.4 mm) (ZRC 2012.1023). A, dorso-lateral margin of carapace; B, anterior view of cephalothorax; C, thoracic sternites 3 and 4, showing thoracic sternal groove and telson; D, thoracic sternites 1–5, showing sternoabdominal cavity and thoracic sternal groove; E, left third maxilliped; F, male abdomen and telson, G, major chela; H, minor chela; I, J, G1; K, female abdomen and telson. Scale bars = 1.0 mm.

Fig. 22. Mariaplax anfracta (Rathbun, 1909). A, B, paratype female (6.1 × 4.0 mm) (USNM 39752); C, paratype male (5.0 × 3.2 mm) (USNM 39752). A, C, overall views of carapace, chelipeds and P2–P4; B, frontal view of cephalothorax.

Fig. 23. Mariaplax anfracta (Rathbun, 1909). A–G, paratype male (5.0 × 3.2 mm) (USNM 39752); H, female (4.1 × 2.8 mm) (ZRC 1965.11.24.6). A, dorso-lateral margin of carapace; B, thoracic sternites 1–4, showing sternoabdominal cavity and thoracic sternal groove; C, thoracic sternites3 and 4, showing thoracic sternal groove and telson; D, right third maxilliped; E, major chela; F, G, G1; H, female abdomen and telson. Scale bars = 1.0 mm.