A revision of selected Tetraphyllidea (Cestoda): Caulobothrium, Rhabdotobothrium, Rhinebothrium, Scalithrium, and Spongiobothrium

This revision was undertaken to improve our knowledge of the species diversity, morphology, host associations, and geographic distributions of Caulobothrium, Rhabdotobothrium, Rhinebothrium, Scalithrium, and Spongiobothrium. The interrelationships among species in these and other tetraphyllidean genera were explored based on phylogenetic analyses of morphological and molecular (18S and 28S rDNA) data. Much of the available type material of species in these genera was examined. In addition, newly collected cestodes were examined from 82 species of batoids, including members of all but 4 of the 17 currently recognized batoid families, collected in numerous localities worldwide. This material included new and previously described species for which 4 new genera with clear affinities to the study genera were erected: Rhanibothrium, Divaricobothrium, Katatanobothrium, and Sungaicestus. Taxonomic treatments of the new and previously described study genera included redescriptions of the type and in some cases descriptions of new species in each genus, based on examinations of specimens with light microscopy and scanning electron microscopy. Taxonomic evaluations determined the validity of 9 Caulobothrium species; 3 Rhabdotobothrium species; 36 Rhinebothrium species; 8 Scalithrium species; and 2 Spongiobothrium species. In addition, 6 study species were considered incertae sedis and Shindeiobothrium karbharae Jadhav, Shinde & Deshmukh, 1981 was considered genus inquirenda et incertae sedis. Bothridial loculi exhibited by the study taxa and other tetraphyllideans were examined in histological section and found to be formed by septa that differ based on their position and internal muscular morphology. Caulobothrium was transferred from the Rhinebothriinae into the Serendipidae, while the remaining study genera and Escherbothrium Berman & Brooks, 1994 were considered to belong in the Rhinebothriinae. The rhinebothriine genera are most species rich in the Indo-Pacific, with 3 of the new genera entirely restricted to that region. Phylogenetic analyses based on morphological and molecular data were largely congruent with each other. Both supported the monophyly of most of the study genera and indicated that Rhinebothrium is paraphyletic. However, Caulobothrium appeared as sister to a large, primarily rhinebothriine clade in analyses of morphological data but as a member of a clade of other tetraphyllideans and a cathetocephalidean in analyses of molecular data.