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Abstract: 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 Martinez-Ramirez, 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 1s considered a synonym of Rhabdochona kidderi Pearse, 1936.
Keywords: nematode parasite, taxonomy, morphology, zoogeography, Teleoste1, Neotropics
The territory of Mexico is very interesting from the zoogeographical ogeographical point of view and many papers dealing with helminth parasites of freshwater fishes in this country have been published, with emphasis on those carried out in central and southern Mexico. However, considering the diversity of aquatic ecosystems and the large number and diversity of fish species in this country, the present knowledge of the Mexican nematode fauna of inland fishes remains insufficient (Moravec 2000a, Caspeta-Mandujano 2005, Salgado-Maldonado 2006).
During studies on the helminth fauna of fishes of the Lacantún River (Usumacinta River basin) in the famous Lacandon rain forest, Chiapas State, southern Mexico, carried out during November 2007, numerous parasitic nematodes were collected. Preliminary results of their examination were published within broader studies on the helminth fauna of fishes of Chiapas (Salgado-Maldonado et al. 2011a,b). Subsequently, results of more detailed studies of these nematodes assigned to Rhabdochona Railliet, 1916 and Spinitectus Fourment, 1884, including the evaluation of their morphology, taxonomy and host-parasite relationships, were also published (Moravec et al. 2009,...