Pseudocryptocoeloma parvum Ward, 1936

Ng, Peter K. L. & Rahayu, Dwi Listyo, 2023, Review of the pilumnid crab genus Lophoplax Tesch, 1918 from the western Pacific, with descriptions of two new species, and the clarification of the identity of Pseudocryptocoeloma parvus Ward, 1936 (Crustacea: Brachyura), Zootaxa 5244 (5), pp. 428-454 : 447-451

Pseudocryptocoeloma parvum Ward, 1936

( Figs. 13–15 )

Pseudocryptocoeloma parvus Ward, 1936: 3 , pl. 1 figs. 7–9; Davie 2002: 426; Ng 1987: 79, 97; Ng et al. 2008: 144.

Material examined. 1 male (8.7 × 6.2 mm) ( NHM 1937.7.15.20), Thursday Island , Torres Strait, Australia, coll. M. Ward , 1937.

Diagnosis. As for genus.

Description of male. Carapace subquadrate, broader than long; dorsal surface gently convex in anterior half, almost flatter on posterior half; regions poorly defined; surface smooth, without granules or obvious rugosities, frontal and anterolateral margins covered by numerous soft setae that obscures margins, rest of carapace glabrous, appearing polished ( Figs. 13A , 14A , 15A ). Frontal margin slightly produced, divided into 2 very low lobes, barely separated by very shallow concavity; lateral lobe not discernible ( Figs. 13A , 14A , 15A ). Anterolateral margin convex; external orbital tooth very low, wide, outer margin 4 times longer than inner margin, separated from first anterolateral tooth by shallow notch; first anterolateral tooth low, wide; second anterolateral tooth low, with outer margin convex ( Figs. 13A , 14A , 15A ). Posterolateral margin gently concave, surface weakly rugose, converging to almost straight posterior carapace margin ( Figs. 13A , 14A , 15A ). Suborbital, subhepatic, pterygostomial and sub-branchial regions smooth ( Fig. 14A ). Orbit transverse, large; supraorbital margin almost straight, entire; suborbital margin gently sinuous, entire, without tooth on inner angle ( Figs. 13A , 14A , 15A, B ). Eyes large with short peduncle and large cornea ( Figs. 13A , 14A , 15A, B ). Antennular peduncle basal article folding transversely ( Figs. 14A , 15B ). Antennal peduncle (basal article) quadrate, immovably fused with epistome but sutures visible; articles 3 and 4 shorter than basal article, flagellum short, not entering orbit; antennule folding transversely ( Figs. 14A , 15B ). Epistome longitudinally wide; posterior margin with wide median triangular lobe with median fissure, separated from lateral part by short fissure; lateral margin almost straight ( Figs. 14A , 15B, C ). Endostome with low oblique ridge on each half.

Third maxilliped relatively short; merus quadrate, anteroexternal angle auriculiform; ischium subrectangular with shallow oblique median sulcus; exopod relatively broad, tip almost reaching distal edge of merus, with long flagellum ( Fig. 15D ).

Chelipeds asymmetrical, relatively short; basis-ischium almost smooth on ventral margin; merus short, unarmed; carpus with low but acute inner distal tooth, dorsal surface smooth ( Figs. 13A, B , 14A–D ); chela enlarged, both chelae similar in structure, outer surface smooth, glabrous, only dorsal margins setose, palm high, fingers shorter than palm, pollex forming gently concave and continuous margin with ventral margin of palm, dactylus meeting pollex at sharp angle, cutting margins of each finger with low, wide teeth ( Figs. 13A, B , 14A–D ).

Ambulatory legs relatively short, stout, without conspicuous teeth or spines; margins covered with similar pubescence on carapace; P3 longest, P5 shortest; merus without cristae on dorsal margin, appearing entire; carpus and propodus smooth; dactylus gently curved along most of length, tip hooked, almost glabrous ( Figs. 13A , 14E ).

Thoracic sternum smooth, weakly setose; sternites 1 and 2 completely fused to form triangular structure; sternite 2 and 3 separated by distinctly sinuous suture; sternites 3 and 4 fused but shallow oblique lateral depression demarcating sternites visible; sternopleonal cavity reaching imaginary line connecting submedian part of coxae of chelipeds; sternite 8 exposed when pleon closed, visible as subquadrate plate ( Figs. 13B , 14F , 15E ).

Pleon triangular, transversely narrow, especially along somites 4–6; all somites and telson free; somite 1 widest, reaching to P5 coxae; somite 2 less than somites 1 and 3; somite 3 wide, reaching condyles of P5 coxae; somites 4 and 5 trapezoidal with gently concave margins; somite 6 rectangular; telson triangular ( Figs. 14F , 15F ).

G1 strongly sinuous, distal part strongly curved, hooked, elongate ( Fig. 15G–J ); G2 short spatuliform ( Fig. 15K ).

Colour in life. Not known.

Remarks. Ward (1936: 4) described this species from 28 males and 26 females from Lindeman Island, Whitsunday Passage, Queensland; with one male with a carapace width of 10.0 mm selected as the holotype. Despite several attempts, we have not been able to examine the types in the Queensland Museum which could not be found during the period of this study because of lockdowns and collection relocation. The present specimen from northeastern Australia, however, agrees very well with the original description and figures and we are confident of its identity.

As the gender of the genus must be neuter (derived from the Greek - coeloma), the species name should be spelled as “ parvum ”.

Habitat. Ward (1936: 4) states that the “species occurs under stones on mud at about half way down the intertidal area.”

Distribution. Known only from northeastern Australia.

Figures

FIGURE 13. Pseudocryptocoeloma parvum Ward, 1936, male (8.7 × 6.2 mm) (NHM 1937.7.15.20), Australia.A, overall dorsal view; B, ventral view of cephalothorax.

FIGURE 14. Pseudocryptocoeloma parvum Ward, 1936, male (8.7 × 6.2 mm) (NHM 1937.7.15.20), Australia.A, frontal view of cephalothorax; B, dorsal view of right cheliped; C, right chela; D, left chela; E, right P5; F, male pleonal somites 1–4.

FIGURE 15. Pseudocryptocoeloma parvum Ward, 1936, male (8.7 × 6.2 mm) (NHM 1937.7.15.20), Australia. A, left side of carapace; B, frontal view of carapace showing antennae, antennules, orbit and epistome; C, posterior margin of epistome; D, left third maxilliped; E, anterior thoracic sternum; F, pleonal somites 1–4; G, left G1 (ventral view); H, distal part of left G1 (ventral view); I, distal part of left G1 (dorso-mesial view); K, left G2. Scales: A–F = 1.0 mm; G, K = 0.5 mm; H–J = 0.2 mm.