Three new species of Rhynchonema (Monhysterida: Xyalidae) from the Brazilian continental shelf, Potiguar Basin.

The taxonomic study of the genus Rhynchonema on the Continental Shelf of the Potiguar Basin, northeastern Brazil, resulted in the description of three new species. These species are differentiated by a combination of characteristics related to the amphideal fovea, cuticle and to the males copulatory apparatus. Rhynchonema laminam sp. nov. is characterized by the cuticle with vacuoles, amphideal sexual dimorphism and amphideal plate (annulation of the cuticle without division and which accommodates the entire amphideal fovea). In addition, it has two precloacal supplements, the spicules are slightly curved, and the gubernaculum presents a dorsal apophysis and a pointed anterior projection. Rhynchonema potiguar sp. nov. does not present a cuticle with vacuoles and amphideal sexual dimorphism is not very evident (amphideal fovea slightly larger in males), the amphideal plate is absent, the spicules are arched, and the proximal portion is spoon shaped, the gubernaculum has a dorsal-caudal apophysis, three papilliform precloacal supplements are present and females present sclerotization in the portion of the vagina in leaf format. Rhynchonema cleoae sp. nov. presents a cuticle with vacuolation and amphideal sexual dimorphism, but the amphideal plate is absent, the spicules are almost in a straight line and the gubernaculum has a singular V shaped morphology. Based on the characteristics of these species, an amendment to the diagnosis of the genus is proposed.