Rediscovery, hosts and systematics of Holothuriophilus trapeziformis Nauck, 1880 (Crustacea, Brachyura, Pinnotheridae)

The type species of Holothuriophilus Nauck, 1880, H. trapeziformis Nauck, 1880 is rediscovered in the type locality, Mazatlan, Sinaloa, Mexico and in a new locality, Zihuatanejo Bay, Guerrero, Mexico. The generic diagnostic features include a smooth, transversally elongated carapace, that is broader than long, widest portion anterior to middle portion and with a cristate anterolateral margin; basal antennal article lacking a conical protuberance; third maxilliped with fused ischium and merus, spoon-shaped dactyl larger than subtrapezoidal propodus which is subequal in length to the carpus; abdomen with six somites and free telson. Hosts recorded for H. trapeziformis include the holothurids Holothuria inornata Semper, 1868, H. lubrica Selenka, 1867 and H. kefersteini Selenka, 1867 (= Paraholothuria riojai Caso, 1964), however, only the former is herein confirmed. Holothuriophilus trapeziformis can be separated from its eastern Pacific congener H. pacificus (Poeppig, 1836) because the fingers of the chela meet when closed instead of leaving a gape as in the latter species.