| dc.description.abstract | The lecanicephalidean tapeworm genus Tetragonocephalum comprises 12 valid species and a species inquirendum. Species in this genus are easily identifiable among lecanicephalideans based on their possession of a unique combination of features: a non-retractable, muscular apical organ; a dumbbell-shaped, rather than saccate, uterus; and a large, rather than small, genital atrium. Valid species of Tetragonocephalum have been described from seven species of stingrays (Dasyatidae) representing the genera Brevitrygon, Himantura, Maculabatis, Pastinachus, and Urogymnus, all from the Indo-Pacific region. Extensive new material from Australia, the Solomon Islands, Japan, Taiwan, Vietnam, Sri Lanka, India, Egypt, Mozambique, and the island of Borneo has allowed for a more complete assessment of the diversity, host associations, and geographic distributions of Tetragonocephalum overall. Selected worms were prepared as whole mounts for examination with light and scanning electron microscopy and as histological sections. The new material suggests that species of Tetragonocephalum parasitize at least an additional 14 species of dasyatid stingrays. The new host records include, for the first time, species in the genera Hemitrygon, Neotrygon, and Taeniura. More detailed study of the fauna of three of the five species of Pateobatis indicated that Pateobatis fai, P. jenkinsii, and P. uarnacoides are parasitized by four, three, and two species, respectively. Four of the species found to parasitize members of the genus Pateobatis are formally described and included in a principal component analysis of morphological characters to determine morphological cohesion of specimens assigned to the new species. A phylogenetic analysis based on 18S, 28S, 5.8S/ITS rDNA sequence data including 25 specimens representing 23 species was conducted using Bayesian inference. Results of the phylogenetic analysis confirm all four described species as distinct from one another, as well as distinct from the three described and 16 undescribed species included in the analysis. The phylogenetic analysis also indicates the presence of two major clades. Morphological characters to support the two clades have yet to be identified. These data corroborated published data that suggest that congeners in the same host species are the rule, not the exception in the genus Tetragonocephalum. Including the previously described species and published reports of undescribed species, as well as the results of this study, the estimate for the number of species in the genus Tetragonocephalum is significantly expanded. | |
