Serendip deborahae n. gen. and n. sp. (Eucestoda: Tetraphyllidea: Serendipidae n. fam.) in Rhinoptera steindachneri Evermann and Jenkins, 1891 (Chondrichthyes: Myliobatiformes: Myliobatidae) from southeastern Ecuador.

Cestodes collected in spiral valves of Rhinoptera steindachneri from the southern coast of Ecuador represent an undescribed species of Tetraphyllidea. The new species has bothridia possessing septa but lacking apical suckers. It is diagnosably distinct from all other tetraphyllidean genera by possessing a scolex comprising 4 triangular bothridia that are fused together forming a platelike structure, each of which is subdivided by 2 simple and 1 bifurcating septa radiating from its base and ringed by marginal loculi; therefore, a new genus is proposed for it. By exhibiting some degree of bothridial fusion, testes arranged in 2 layers in the proglottis and postovarian testes, the new species appears to be a member of a clade containing Dioecotaenia, Duplicibothrium, and Glyphobothrium. The new species possesses vitelline fields that converge dorsally in each proglottis, except for the ovarian and terminal genitalia areas, a feature that has been reported previously only in Duplicibothrium and Glyphobothrium. Furthermore, Duplicibothrium and Glyphobothrium, like the new species, are markedly protandric. Therefore, we propose that Duplicibothrium, Glyphobothrium, and the new species comprise the sister group of the Dioecotaeniidae, and propose a new family name for the clade. Tritaphros is rejected as a possible sister group for the clade; suggested alternatives include some species of Caulobothrium, Rhodobothrium, or some members of the Phyllobothrium centrurum group.