Buticulotrema stenauchenus n. gen., n. sp. (Digenea: Opecoelidae) from Malacocephalus occidentalis and Nezumia aequalis (Macrouridae) from the Gulf of Mexico

Buticulotrema stenauchenus n. gen., n. sp. (Opecoelidae: Opecoelinae) is described from the macrourid fishes Malacocephalus occidentalis Goode and Bean, 1885, and Nezumia aequalis Günther, 1878, collected in June 1971 from the DeSoto Canyon area of the Gulf of Mexico at a depth of 495 m. Eight of 25 (32%) M. occidentalis and 1 of 8 (13%) N. aequalis examined were infected with the new opecoelid. Specimens of Bathygadus macrops Goode and Bean, 1886, and Coelorhynchus Risso, 1810, collected at the same time were not infected with B. stenauchenus. The new genus most closely resembles Genitocotyle Park, 1937, but differs in that it lacks an accessory sucker behind the genital pore, contains a blind rather than canalicular seminal receptacle, and has a slightly pedunculate acetabulum, a pharynx that is longer than wide, and a distinctive, long-necked, bottle-shaped body. Buticulotrema stenauchenus is also similar to Pseudopecoelus von Wicklen, 1946, but the latter lacks a blind seminal receptacle.