n. sp. (Eucestoda: Proteocephalidae), a parasite of (Linnaeus, 1758), with redescription of (Santos and Rolas, 1973) from the Brazilian Amazon.

is the most diverse genus among proteocephalids, composed of species commonly found parasitizing snakes worldwide. However, the diversity of in the Neotropical region is still underestimated. This study describes n. sp. found parasitizing in the State of Amapá, Brazil. Additionally, we redescribe based on a re-examination of type series and newly collected material from in the State of Pará, Brazil. The new species differs from its congeners in the following characteristics: scolex width, number of testes, relative length of the cirrus-sac, absence of a vaginal sphincter, presence of a vestigial apical organ resembling a sucker, and relative size of the ovary in relation to the surface of the proglottid. Furthermore, we provide taxonomic information for not reported in the original description, including morphology of embryophore, uterine development, and the absence of the vaginal sphincter in the species. n. sp. represents the 21st- species described in snakes -from the Neotropical region and the first formally described in the Brazilian Amazon. Additionally, we provide the first ultrastructural analysis, a new host, and locality records for .