An unusual new species at risk, parasite of a critically endangered guitarfish, Pseudobatos horkelii (Elasmobranchi: Rhinobatidae): insights into the phylogeny of Acanthobothrium (Cestoda: Onchoproteocephalidea)

Abstract

Guitarfishes comprise a group of elasmobranchs with a high risk of extinction and whose parasite fauna is largely unknown in the Southwest Atlantic Ocean. The genus Acanthobothrium is one of the most diverse groups of cestodes from elasmobranchs. In the present study, the erection of the new species Acanthobothrium goleketen n. sp., parasitizing Pseudobatos horkelii, is proposed based on both morphological and molecular characters. The new species is assigned to the morphological category 3 and is differentiated morphologically from all congeners in that category and those of the related category 4 by the type of apolysis, total length, number of proglottids, scolex configuration, size of various bothridial structures, length of cephalic peduncle and number of testes. Knowledge about the phylogenetic relationships among Acanthobothrium species is still incipient. This study discusses the interspecific relationships of all formally described and sequenced species of Acanthobothrium on the basis of phylogenetic reconstructions using Bayesian Inference, Maximum Likelihood and Maximum Parsimony. No apparent phylogenetic pattern was observed among species with geographical affinity or species from closely related hosts. In contrast, some species with morphological similarities were grouped in highly supported clades. The new species was catalogued as Critically Endangered in accordance with the status of its host. The great diversity of chondrichthyans in the Argentine Sea and the lack of information about their parasite fauna, highlight the need to increase diversity studies and complete the assignment of conservation categories.