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The phylogenetic relationships of Cucullanidae were explored using near-complete sequences of the 18S rDNA (rRNA gene). Sequences (1,750-1,760 bp) were obtained from 7 species of Cucullanidae belonging to 3 genera, Cucullanus (2 spp.), Dichelyne (2 spp.), Truttaedacnitis (3 spp.), and 1 species of Quimperiidae ( Paraseuratum sp.). These sequences were aligned with those of 128 other nematode species available in GenBank, including 3 other cucullanids (Dichelyne mexicanus, Cucullanus robustus, and Cucullanus baylisi) and 2 non-cucullanid seuratoids (Paraquimperia africana, and Linstowinema sp.). Bayesian (BPP) and maximum likelihood (ML) analyses of 2 different datasets strongly supported a monophyletic Cucullanidae. Bayesian analysis placed this family as the sister group to a clade containing species of Diplogasterida, Strongylida, Rhabditida, and Tylenchida with very strong support. Neither BPP nor ML analyses recovered a close relationship of Cucullanidae to Ascaridida. None of the 3 non-cucullanid seuratoid species were sister to Cucullanidae, nor did they form a monophyletic group of their own, which questions the monophyly of Seuratoidea and the relationships among species within this superfamily. The 3 genera of cucullanids were also not monophyletic, although morphologically similar species such as the 2 species of Cucullanus from Neotropical catfishes and 2 species of Dichelyne from Nearctic ictalurid catfishes were sister taxa with strong support. The results were ambiguous with respect to the relationship of 2 Truttaedacnitis spp. in Nearctic freshwater fishes but do not support Truttaedacnitis heterodonti, a parasite of heterodontid sharks, as belonging to this genus. The study shows that all aspects of the conventional classification of Seuratoidea and its taxa should be scrutinized by even more extensive sampling across hosts and habitats.

A new nematode species, Cucullanus angeli n. sp., is described from specimens recovered from the intestine of Vieja intermedia (Günther, 1862) from the Lacantun River, State of Chiapas, Mexico. It is characterized largely by having an unusual distinct unpaired median papilla present on anterior cloacal lip in the male and the situation of phasmids (close to eighth pair of papillae); it is further characterized by equal spicules (length 175-475 microm), distribution of caudal papillae, a preanal sucker surrounded by first and second pair of papillae, and conical tail in both sexes, ending in small terminal digitiform process (being more conspicuous in the female).

Helminths of the spiral intestine of neotropical freshwater stingrays (Potamotrygonidae) were examined in Peru for the first time. The stingrays examined for helminths included Paratrygon aiereba, Potamotrygon motoro, and Potamotrygon cf. castexi. Present in P. aiereba were the cestodes Nandocestus guariticus (Marques, Brooks, and Lasso, 2001) n. gen. n. comb., Rhinebothrium copianullum n. sp., Rhinebothrium sp. 1, Rhinebothroides sp., Potamotrygonocestus cf. fitzgeraldae, and 1 species each of Cucullanus and Rhabdochona. Nandocestus n. gen. is erected to house N. guariticus, which is formally transferred from Anindobothrium Marques, Brooks, and Lasso, 2001. The new genus is unique among phyllobothriids in its possession of circummedullary vitelline follicles and a submarginal genital pore, in combination with bothridia with a single apical sucker and marginal bothridial loculi. The helminths of P. motoro included the cestodes Paraoncomegas araya, Acanthobothrium peruviense n. sp., Acanthobothrium cf. ramiroi, Rhinebothrium sp. 1, Rhinebothroides sp. 1, Potamotrygonocestus sp., the nematode Brevimulticaecum regoi, a species of Cucullanus, and a species of the digenean superfamily Diplostomoidea. The helminths of P. cf. castexi included the cestodes P. araya, N. guariticus n. gen. n. comb., Acanthobothrium cf. peruviense, Potamotrygonocestus sp., Rhinebothrium sp. 1, Rhinebothroides sp. 2, the nematode species Echinocephalus daileyi and B. regoi, 1 species each of Cucullanus, Rhabdochona, and Procamallanus, and a species of the digenean superfamily Hemiuroidea. All taxa were examined via light microscopy; the cestode taxa were also examined using scanning electron microscopy. Each helminth species recorded in this study is a first report from Peru. The study suggests that the diversity and host specificity of the cestodes in potamotrygonid stingrays may be greater than previously thought. The known numbers of genera and species of tetraphyllidean cestodes parasitizing neotropical freshwater stingrays are now 6 and 22, respectively.