Upogebia hibiki Ando & Karasawa, 2010, sp. nov.

Upogebia hibiki sp. nov.

(Fig. 3A–G)

Diagnosis. Rostrum triangular, about as long as wide at the base, with rounded tip; dorsal surface with weak median depression. Gastric region much longer than wide with shallow median groove extending to midlength; 3 rows of tubercles present, parallel to lateral groove; lateral ridge strong, slightly divergent posteriorly, posterior half tuberculate; lateral groove deep. Pereiopods 1 subchelate, equal, similar in shape. Dactylus slender, elongate; occludent margin with low, broad tooth on proximal third; dorsolateral and ventrolateral ridges smooth; dorsal ridge ornamented with minute tubercles proximally. Fixed finger short. Palm about 2/3 times as long as dactylus, much longer than high; lateral surface moderately convex longitudinally, bearing 3 or 4 rows of minute, conical tubercles medially; 2 dorsolateral grooves present, shallow with small setal pits; dorsal margin gently convex, rimmed, with minute setal pits; ventral margin gently concave; mesial surface slightly convex longitudinally, bearing 12–15 oblique ridges on ventral half, strong, arched ridge along dorsal margin on dorso-distal part, and short transverse ridges on dorsal half.

Etymology. The trivial name is derived from “Hibiki-Nada”. The name hibiki is an arbitrary combination of letters.

Description. Rostrum triangular, about as long as wide at the base, with rounded tip; lateral margin nearly straight; dorsal surface with weak median depression. Gastric region much longer than wide, about half as wide as long, with shallow median groove extending to mid-length; 3 rows of tubercles present, parallel to lateral groove; lateral ridge strong, slightly divergent posteriorly becoming narrower posteriorly, posterior half tuberculated; lateral groove deep, sinuous. Cervical groove well defined. Cardiac region poorly preserved, smooth.

Pereiopods 1 subchelate, equal, similar in shape. Dactylus slender, elongate, gently curved ventrally, with acutely pointed tip; occludent margin with low, broad tooth on proximal third; dorsolateral and ventrolateral ridges smooth; dorsal ridge ornamented with minute tubercles proximally. Fixed finger short about 15% dactylus length, with acutely pointed tip. Palm about 2/3 as long as dactylus, about 2 times longer than high; lateral surface moderately convex longitudinally, bearing 3 or 4 rows of minute, conical tubercles medially; 2 dorsolateral grooves present, shallow, parallel to dorsal margin, with small setal pits; dorsal margin gently convex, rimmed, with minute setal pits; ventral margin gently concave; mesial surface slightly convex longitudinally, bearing 12–15 oblique ridges on ventral half, strong, arched ridge along dorsal margin on dorso-distal part, and short transverse ridges on dorsal half. Carpus short, about 1/3 palm length, triangular, tapering distally, with granulated dorsal margin.

Abdominal somites 5–6 and telson poorly preserved. Exopod of uropod subtriangular with marginal ridge; posterior margin slightly sinuous.

Remarks. Upogebia hibiki sp. nov. is closest to Upogebia mizunamiensis, from the lower Miocene Mizunami Group in having oblique ridges on the mesial surface of the palm of pereiopod 1. However, the new species differs from U. mizunamiensis in having a strong, arched ridge on the dorso-distal part of the mesial surface of the palm and in having the carapace with a narrow gastric region and a triangular rostrum. The new species also resembles Upogebia striata, from the middle Miocene Katsuta Group, but differs in having a strong, arched ridge on the dorso-distal part of the mesial surface of the palm. Adittionally, Upogebia striata has a slender, elongate palm.