Some nematodes from fishes of the Lacantún River in the Lacandon rain forest of Chiapas State, southern Mexico, including Cucullanus potamarii sp. n. (Cucullanidae) from the endemic catfish Potamarius usumacintae (Ariidae).

During November of 2007, parasitic nematodes were collected from 161 specimens of 32 freshwater fish species in the Lacantún River of the Lacandon rain forest of Chiapas, southern Mexico. Recent detailed morphological and taxonomic studies of this material revealed the presence of 17 nematode species (12 adult and 5 larval) of nine families, including Cucullanus potamarii sp. n. from the intestine of the ariid catfish Potamarius usumacintae Betancur-R et Willink, which is endemic to the Usumacinta River basin to which the Lacantún River belongs. This new species is mainly characterised by deirids and the excretory pore located far posterior to the level of the oesophago-intestinal junction, which is an almost unique feature among its congeners. Most parasites are briefly described and illustrated, and problems concerning their morphology, taxonomy, hosts and geographical distribution are discussed. Some findings represent new host and geographical records. Cucullanus oaxaquensis Caspeta-Mandujano, Salgado-Maldonado et Martínez-Ramírez, 2010 is considered a junior synonym of Cucullanus angeli Cabañas-Carranza et Caspeta-Mandujano, 2007, and Neocucullanus marcelae Ramallo, 2012 a species inquirenda. Based on absence of relevant morphological differences, Rhabdochona ictaluri Aguilar-Aguilar, Rosas-Valdez et Pérez-Ponce de León, 2010 is considered a synonym of Rhabdochona kidderi Pearse, 1936.