A new species of Proteocephalus, P. joanae sp. n„ is described from the intestine of the colubrid snake, Xenodon neuwiedi (Günther, 1863) (Serpentes: Xenodontinae), from Brazil. The new species differs from all other members of Proteocephalus by possessing a swollen elongated posterior part of the scolex herein considered as a metascolex. Furthermore, it is the only member of New World Proteocephalus possessing a voluminous glandular apical organ larger than suckers. P. joanae is also characterized by very elongated gravid proglottides. This is the first member of the Proteocephalidea occurring in Xenodon. Even though the species differs significantly from other species of the genus Proteocephalus, which currently contains many species that are morphologically very distinctive, it seems prudent to refrain from reworking the classification of the group until accurate redescriptions of Neotropical species can be conducted, preferably based on examination of type and freshly collected material. The definition of the metascolex is discussed herein.
As part of a metazoan parasite survey of elasmobranchs from Malaysian Borneo, specimens of Rhoptrobothrium Shipley et Hornell, 1906 were collected from the eagle rays Aetomylaeus maculatus (Gray) and Aetomylaeus niehofii (Bloch et Schneider). The type species is redescribed from its type host, and a neotype specimen is designated. In addition, three new species of Rhoptrobothrium are described: R. chongi sp. n., R. gambangi sp. n. and R. limae sp. n. Rhoptrobothrium myliobatidis conspicuously differs from the three new species in its lack of a secondary areola; R. limae is distinguished from R. chongi and R. gambangi based on its greater total length; R. chongi possesses conspicuously stalked remi, while R. gambangi possesses short remi, often folded anteriorly. Rhoptrobothrium is somewhat unusual among tetraphyllideans in its possession of a ''metascolex,'' a character it shares with other taxa in the Thysanocephalinae (i.e., Myzocephalus Shipley et Hornell, 1906, Myzophyllobothrium Shipley et Hornell, 1906 and Thysanocephalum Linton, 1889). The morphology of the ''metascolex'' of Rhoptrobothrium is investigated and new terminology is suggested to standardise the names given to structures constituting a metascolex. As a result, Rhoptrobothrium is considered to possess cephalic peduncle extensions, termed remi. In Rhoptrobothrium, each remus bears, at its distal end, a primary areola, and, in the case of the three new species, also a secondary areola proximal to the primary areola. Myzocephalus and Myzophyllobothrium are tentatively considered to possess remi; the configuration of the ''metascolex'' of Thysanocephalum, however, is not considered homologous to the condition in the other three genera currently placed in the Thysanocephalinae.