Authors

L Van Der Spuy¹; N J Smit²; B C Schaeffner¹;  ¹ North-West University Water Research Group, South Africa;  ² Water Research Group, Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa, South Africa

Discussion

A total of over 200 valid species of the cestode genus Acanthobothrium van Beneden, 1849 are currently recognised worldwide. As part of a larger study on the parasites of elasmobranchs in South Africa, four morphologically distinct species of Acanthobothrium were collected from eight specimens of Raja straeleni Poll. Of all skates observed for internal parasites, two specimens were parasitised by all four morphotypes, while two were parasitised with three, two with two, and two skates with a single morphotype. In order to classify these species, they were first compared to congeners using the classification system established by Ghoshroy and Caira in 2001. Hence, they were all identified as category 2 species, which, at present, include 47 recognised species of Acanthobothrium. The South African species exhibit postovarian testes - a most intriguing and highly unusual feature among species of Acanthobothrium, instant­ly differentiating them from most congeners. This feature has been reported from only 12 congeners, which have been previously considered to be restricted to waters of the Indo-Pacific Ocean, from which only two belong to the same category as the new congeners. Regarding the legitimacy of the four South African morphotypes, the only two other category 2 species reported to exhibit postovarian testes are A. popi Fyler, Caira et Jensen, 2009, and A. bobconniorum Fyler et Caira, 2010. These differ, however, in a combination of morphological features from the four morphotypes of the present study, which, in turn, were described as species new to science: A. microhabentes, A. microtenuis, A. crassus, and A. dolichocollum. The four new species represent the first species of Acanthobothrium re­ported from southern Africa, and were also the first speciesexhibiting postovarian testes from the southern Atlantic Ocean. It is estimated that an average of four cestode species parasitise a single elasmobranch host species. However, with merely 9 % (18 of 204) of elasmobranchs off south­ern Africa examined for the presence of cestodes, it is ex­pected that there is an immense hidden species diversity of cestodes infecting elas­mobranchs in South African waters, certainly much higher than currently known. As a consequence, the diversity of cestodes in the waters of South Africa is predicted to be either equal to, or, more likely, greater than the diversity of the chondrichthyan hosts present in these waters. Additional large-scale surveys on elasmobranch parasites will, with­out any doubt, lead to numerous new species discoveries in the future. The four species were recovered from a previously unexplored host and locality, expanding the host associations and geographical distribution of the genus in the south-eastern Atlantic Ocean. The work presented here was published recently in Folia Parasitologica (doi: 10.14411/fp.2020.036).