Lophoplax symmetrinuda ( Edmondson, 1951 )

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 : 444-446

Lophoplax symmetrinuda ( Edmondson, 1951)

( Fig. 12 )

Pseudocryptocoeloma symmetrinudus Edmondson, 1951: 233 , fig. 34; Serène 1968: 86; Ng 1987: 79, 97; Ng et al. 2008: 144; Marumura & Takeda 2012: 192, figs. 2A, 3, 4; Maenosono 2019: 32, figs. 8B, 10, 13B, 14K, L.

Lophoplax symmetrinudus — Takeda & Kurata 1984: 201; Takeda & Marumura 1995: 90.

Type material. Holotype: male (6.5 × 5.0 mm) ( BPBM 5109 ), low tide, table reef, Siufaga, Tau, Samoa, coll. W. Harris, 1937.

Diagnosis. Carapace transversely subovate ( Fig. 12A ; Marumura & Takeda 2012: fig. 3A; Maenosono 2019: fig. 10A); epigastric, protogastric, hepatic, cardiac and intestinal areolets all glabrous, prominent, smooth; epigastric areolets relatively wide, ovate, short ( Fig. 12A ; Marumura & Takeda 2012: fig. 3A; Maenosono 2019: fig. 10A); protogastric areolet prominent, transversely ovate positioned obliquely ( Fig. 12A ; Marumura & Takeda 2012: fig. 3A; Maenosono 2019: fig. 10A); cardiac areolet medially separated, each element positioned obliquely ( Fig. 12A ; Marumura & Takeda 2012: fig. 3A; Maenosono 2019: fig. 10A); hepatic areolet swollen, long, reaching only to base of second anterolateral tooth ( Fig. 12A ; Maenosono 2019: fig. 10A); external orbital tooth wide, low ( Fig. 12A ; Maenosono 2019: fig. 10A, B); tips of external orbital and anterolateral teeth low, rounded ( Fig. 12A ; Maenosono 2019: fig. 10A, B); junction between antero- and posterolateral margins demarcated by second anterolateral tooth without additional lobes or tubercles ( Fig. 12A ; Maenosono 2019: fig. 10A, B); epistome relatively narrow longitudinally ( Maenosono 2019: fig. 10C); median lobe of posterior margin of the epistome broadly triangular, with lateral margins gently concave ( Maenosono 2019: fig. 10C). Third maxilliped with merus quadrate, ischium short ( Fig. 12B ). Dorsal and lateral surfaces of carpus of cheliped rugose; cheliped fingers not distinctly bent, pollex subparallel with the ventral margin of palm ( Maenosono 2019: fig. 10D). P2–P5 very short, not elongate ( Fig. 12C ); outer surface of the P3–P5 merus, carpus and propodus smooth ( Fig. 12A ). Male pleonal somites 4–6 transversely wide, telson wider than long, semicircular ( Fig. 12D ; Maenosono 2019: fig. 13B). G1 slender, sinuous, distal part gently curved upwards ( Fig. 12E, F ; Marumura & Takeda 2012: fig. 4A, B; Maenosono 2019: fig. 14K, L).

Colour in life. Background colour white; setae brown; epigastric, protogastric and hepatic areolets bright red; cardiac areolets pale red to red ( Marumura & Takeda 2012: fig. 2A; Maenosono 2019: fig. 8B).

Remarks. Lophoplax symmetrinuda is arguably the most distinctive member of the genus Lophoplax as currently diagnosed: it differs markedly from all congeners in its transversely subovate carapace ( Fig. 12A ; Marumura & Takeda 2012: fig. 3A; Maenosono 2019: fig. 10A); the wide and low external orbital and anterolateral teeth ( Fig. 12A ; Maenosono 2019: fig. 8A, B); the absence of tubercles or lobes at the junction between the antero- and posterolateral margins ( Fig. 12A ; Maenosono 2019: fig. 8A, B); the proportionately shorter merus and ischium of the third maxilliped ( Fig. 12B ); the comparatively shorter ambulatory legs, especially the merus ( Fig. 12C ; Maenosono 2019: fig. 8B); and the distinctly wider male pleon ( Fig. 12D ; Marumura & Takeda 2012: fig. 4C; Maenosono 2019: fig. 8B). Despite these characters, the presence and arrangement of the gastric, cardiac and hepatic lobes agrees well with other Lophoplax species, and as such we retain it in this genus for the time being, as first suggested by Takeda & Kurata (1984) and Takeda & Marumura (1995).

The original figures of the species by Edmondson (1951: fig. 34a–d) are inaccurate, the carapace in particular appearing quadrate rather than ovate and the dentition being incorrectly depicted ( Fig. 12 ).

Edmondson (1951: 235) comments on why it should be in Pseudocryptocoeloma are brief and non-informative: “The genus Pseudocryptocoeloma was established by Ward in 1936 to provide for the species P. parvus , described from Lindeman Island, Queensland. The new species differs from the Australian form in the arrangement of the nude areas of the carapace. In P. parvus the entire median and posterior portions of the carapace are bare.” Maenosono (2019) described and figured the species at length and in the present examination of the holotype male agrees well with his account, notably in the form of the male pleon and G1.

Habitat. The type male was collected on a table reef in the intertidal zone of a reef. Maenoson (2019) collected the species from intertidal reef habitats as well in Japan .

Distribution. Known from Samoa and the Ryukyus, Japan.

Figures

FIGURE 12. Lophoplax symmetrinuda (Edmondson, 1951), holotype male (6.5 × 5.0 mm) (BPBM 5109), Samoa. A, dorsal view of carapace; B, left third maxilliped; C, left P5; E, left G1 (ventral view); F, left g1 (dorsal view); G, left G2; D, pleon.