Thynnascaris reliquens sp. n. and T. habena (Linton, 1900) (Nematoda: Ascaridoidea) from fishes in the northern Gulf of Mexico and eastern U.S. seaboard.

Thynnascaris reliquens sp. n. is described from the type host, the sheepshead, Archosargus probatocephalus (Walbaum), and other fishes of the northern Gulf of Mexico and southern Florida, including the Gulf toadfish, Opsanus beta (Goode and Bean); the spiny boxfish, Chilomycterus schoepfi (Walbaum); the slippery dick, Halichoeres bivittatus (Bloch); and the Atlantic croaker, Micropogon undulatus (Linnaeus). Its salient characters are: length up to approximately to 12.5 cm; lips broad, with pedunculate pulp and equatorially constricted flanges; esophagus 8 to 12% and spicles 3 to 6% of body length; preanal and postanal papillae up to 33 and 6 pairs, respectively. In the type host, some adults attained a considerably greater size than in other hosts, and their labial morphology changed as the maximum length was approached. Thynnascaris habena is redescribed from the oyster toadfish, Opsanus tau (Linnaeus), its type host, on the basis of examination of specimens collected from Massachusetts, Virginia, and Georgia. Thynnascaris melichthysi (Olsen, 1952) and T. ogcocephali (Olsen, 1952) are transferred from the genus Contracaecum as new combinations.