Frezella gen. n. is proposed to accommodate Frezella vaucheri sp. n. from poorly known auchenipterid fish, Tocantinsia piresi (Miranda Ribeiro), from the Xingú River, one of the principal tributaries of the lower Amazon River in Brazil. The new genus belongs to the Proteocephalinae because of the medullary position of the testes, ovary (yet some follicles penetrate to the cortex on the dorsal side), vitelline follicles and uterus. It differs from other proteocephaline genera in the morphology of the scolex, which includes a metascolex composed of two distinct zones: anterior, strongly wrinkled part posterior to the suckers, and posterior, sparsely folded zone. Frezella can also be differentiated by having the internal longitudinal musculature hypertrophied laterally on both sides, the presence of some ovarian follicles in the cortex on the dorsal side and the presence of additional pair of tiny, thin-walled osmoregulatory canals situated slightly dorsomedian to ventral canals. Frezella vaucheri is the first helminth parasite reported from T. piresi, which occurs in the lower reaches of the Amazon and Tocantins River basins in Brazil.

Departamento de Parasitologia Animal Universidade Federal Rural do Rio de Janeiro Seropedica Rio de Janeiro Brazil

Department of Invertebrates Natural History Museum Geneva Switzerland;

Institute of Parasitology Biology Centre of the Czech Academy of Sciences Ceske Budejovice Czech Republic;

Programa de Pos Graduacao em Biologia Animal Universidade Federal Rural do Rio de Janeiro Seropedica Rio de Janeiro Brazil;

References provided by Crossref.org

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