Revision of the Lecanicephalidean Genus Flapocephalus Deshmukh, 1979 (Eucestoda) from Cowtail Rays (Genus Pastinachus Rüppell) (Myliobatiformes: Dasyatidae Jordan and Gilbert) with the Description of Four New Species

The genus Flapocephalus Deshmukh, 1979, is a little-known group of lecanicephalidean cestodes parasitizing cowtail rays (genus Pastinachus Rüppell) mainly in the Indo-Pacific region. Since the erection of the genus, with Flapocephalus trygonis Deshmukh, 1979, as the type species, and the description of a second species, Flapocephalus saurashtri Shinde and Deshmukh, 1979, both from Pastinachus sephen (Fabricius) from India, reports of this genus have been restricted mainly to brief mentions or discussion of its validity and taxonomic placement. More recently, phylogenetic analyses based on molecular sequence data that included specimens of Flapocephalus have supported Flapocephalus as a distinct genus allied with the Polypocephalidae Meggitt, 1924. Limited by the amount of detail provided in the original descriptions, the unavailability of type material, and the lack of a detailed generic diagnosis, we aimed to fully characterize the genus based on newly collected specimens. A total of 38 specimens of Pastinachus, representing 3 of the 5 described species and 1 undescribed species, from throughout the Indo-Pacific region were examined for specimens of Flapocephalus. Worms were prepared for examination with light and scanning electron microscopy and as histological sections. A subset of specimens was included in a phylogenetic analysis based on data for a portion of the 28S rDNA gene. Overall, these specimens were found to include the type species, 4 new species that are described herein (Flapocephalus monostylorchis Hanselman and Jensen n. sp., Flapocephalus capitonis Hanselman and Jensen n. sp., Flapocephalus rudkinorum Hanselman and Jensen n. sp., and Flapocephalus infundibulapex Hanselman and Jensen n. sp.), and 4 putative new species. Flapocephalus trygonis is redescribed from specimens from Pastinachus ater (Macleay) from Sri Lanka, and a neotype is designated. The newly described species are distinct genetically and can be distinguished morphologically from the existing species and one another based on a combination of total length, the shape of the apical organ, and the arrangement of testes and vitelline follicles. A revised diagnosis of the genus and a key to the described species are presented, as is a hypothesis of the interrelationships resulting from a maximum likelihood analysis including 4 of the 5 described species and the 4 putative new species. The presence of 4 glandular, sac-like structures surrounded by scolex proper, with channels that open to the outside at the base of the apical organ, is reported in lecanicephalidean tapeworms for the first time.