A new cucullanid species (Nematoda) from Ageneiosus ucayalensis Castelnau, 1855 (Pisces: Auchenipteridae) from Pará, Brazil.

Cucullanus ageneiosus n. sp. (Nematoda: Cucullanidae) is described from the intestine of the Ageneiosus ucayalensis , from the Guajará Bay, Belém, Pará, Brazil. The new species is characterized mainly by arrangement of male caudal papillae, and the position of lateral phasmids immediately posterior of 10th papillae, markedly short and unequal spicules, a precloacal sucker, and the presence of an unpaired median papilla just of the anterior cloacal lip.