Revision of the East Asian genus Ditrema (Embiotocidae), with description of a new subspecies

Abstract

A review of the species and subspecies of Ditrema from East Asia recognized the following taxa: D. jordani Franz, 1910, D. temminckii pacificum subsp. nov., D. t. temminckii Bleeker, 1853, and D. viride Oshima, 1940. Ditrema jordani is characterized by a coppery-red body when fresh, the posterior end of the dorsal-fin base anterior to that of the anal-fin base, a dark rounded marking on the anterior suborbital area margined with white lines or a broad dark inverse trapezoid marking on the anterior part of the suborbital region, the lower half of the spinous portion of the dorsal fin often with a longitudinal black stripe, and a faint longitudinal dark line along the anal-fin base. Ditrema temminckii is characterized by a silvery body, usually bluish dorsally when fresh, a black oblique band on the anterior suborbital area, the spinous portion of the dorsal fin with a black distal margin, and no dark line along the anal-fin base. Ditrema t. pacificum, mainly distributed along the Pacific Ocean coast, differs from D. t. temminckii, mainly distributed along the coast of Sea of Japan, in lacking a dark spot on the anterior portion of the preopercle (vs. dark spot present in the latter), but having a black line along the posterior margin of the pelvic-fin spine (vs. black spot anteriorly on base of pelvic fin), fewer dorsal-fin spines (usually 9 or 10 vs. 10 or 11), more dorsal-fin soft rays (mode 21 vs. mode 20), and longer pectoral, pelvic, and caudal fins. The two nominal species (D. smitti and D. leave) are regarded as junior synonyms of D. t. temminckii. Ditrema viride is characterized by a silvery, dorsally yellowish-green body when fresh, 9–11 dorsal-fin spines (mode 10), a dark triangular marking on the anterior suborbital area, the spinous portion of the dorsal fin with a black distal margin, a longitudinal black line along the anal-fin base and the pelvic fin slightly darkish, and lacking a black spot anteriorly on the base. Neotypes are designated for D. jordani and D. viride. A key to the species and subspecies of Ditrema is provided.