Lophoplax takakurai Sakai, 1935a

Lophoplax takakurai Sakai, 1935a View in CoL

( Figs. 4 View Fig , 5 View Fig )

Lophoplax takakurai Sakai, 1935a: 82 View in CoL , text-fig. 15, pl. 7, fig. 2; Sakai, 1935b: 188, frontispiece, fig. 2; Sakai, 1939: 567, pl. 67, fig. l; Sakai, 1976: 541 pl. 191, fig. 4, text-fig. 288; Ng, 1987: 79, 100; Takeda, 1993: 41; Ng et al., 2008: 143; Takeda & Komatsu, 2018: 176, fig. 7; Takeda & Komatsu, 2023: 167.

Material examined. 1 male (5.0 × 4.2 mm) (NSMT-Cr S 1254), Futami Bay , Chichi-jima [= Island], Ogasawara Islands, Japan, 27°04.77′N 142°11.68′E to 27°04.76′N 142°11.73′E, 42.2– 41.6 m, R / V Koyo, 2010 cruise, station KY-10-25, 9 July 2010 GoogleMaps .

Diagnosis. Carapace frontal margin gently convex, smooth, produced anteriorly, lateral lobe not visible ( Fig. 4A, B View Fig ); epigastric areole barely visible; protogastric lobe low, with granular surface ( Fig. 4B View Fig ); metabranchial region with low granules ( Fig. 4B View Fig ); median lobe on posterior margin of epistome subtruncate in form ( Figs. 4E View Fig , 5E View Fig ). Distal margin of ischium of third maxilliped with row of closely set low granules ( Fig. 4C View Fig ). P2–5 merus extensor margin P2–5 with low proximal tooth ( Fig. 5F, G View Fig ). Cheliped carpus dorsal surface with longitudinal areole separated by groove from swollen lateral margin ( Fig. 4A, I View Fig ); proximal basal part of male chela covered with strong tubercles ( Fig. 4G View Fig ). Male thoracic sternum anteriorly relatively narrower ( Fig. 4F View Fig ). G1 strongly sinuous, distal part of G1 gently recurved ( Fig. 5I, J View Fig ). G2 sigmoid, about ¼ length of G1.

Remarks. Lophoplax takakurai was described on the basis of a female (11.0 × 9.0 mm) collected off Yoshihama, west of Sagami Bay, and later reported from off Mikawa Bay (south of Nagoya) ( Sakai, 1935a, b, 1976). Takeda (1993) subsequently recorded the species from Shibushi Bay in Kagoshima, with Takeda & Komatsu (2018, 2023) recording it from the Ogasawara Islands. The whereabouts of the type specimen is not known but appears to be lost. The present specimen matches the type description and figures of Sakai (1935a, 1939, 1976) well, especially in the general carapace features and proportions of the ambulatory legs. Significantly, Sakai (1935a: text-fig. 15c; present Fig. 5B View Fig ) figured the third maxilliped showing a row of closely set granules on the distal margin of the ischium, a character also distinct in the present male specimen ( Fig. 4C View Fig ). As such, we are confident of its identity. For the moment, L. takakurai , as defined by Takeda & Komatsu (2018) and the present study, is clearly recognisable, so a neotype designation does not appear to be necessary.

Although L. takakurai differs markedly from L. bicristata in many characters of the carapace and pereopods, both species have generally similar carapace shape and features. In addition, both species have a stouter G1 ( Figs. 3F–I View Fig , 5I, J View Fig ) compared to more typical pilumnids. It is therefore reasonable to retain both species in Lophoplax for the time being.

Lophoplax takakurai occurs on muddy bottoms 41.6–100 m in depth ( Sakai, 1976; Takeda & Komatsu, 2018).