Two New Cestode Species from the Dwarf Whipray, Himantura walga (Batoidea: Dasyatidae), from Borneo, with Comments on Site and Mode of Attachment

Abstract

Spiral intestines of 12 specimens of the dwarf whipray, Himantura walga, collected from Malaysian Borneo in 2002 and 2003, were examined for cestodes. These yielded a new species of Acanthobothrium (Tetraphyllidea) and a new species of Echinobothrium (Diphyllidea), both of which are described. Acanthobothrium marymichaelorum n. sp. is a category 1 species. It differs from all but 4 of its category 1 congeners in its possession of postovarian testes. It also differs from these 4 species in its possession of fewer testes, shorter length, fewer proglottids, and/or shorter posterior loculus. Echinobothrium minutamicum n. sp. differs from its congeners in its possession of outer hooks in the dorsal and ventral rostellar groups that are trifid; it is also the smallest member of its genus. The spiral intestine of H. walga consisted of 12 mucosal chambers. Most (89%) of the 35 specimens of E. minutamicum n. sp. for which chamber data were generated were found in chambers 2-4. In contrast, the 57 specimens of A. marymichaelorum n. sp. occurred throughout chambers 5-12, with 86% in chambers 6-10. The modes of attachment of both cestode species were similar, i.e., both embedded their scolex within the lumen of a mucosal crypt with the hooks and/or spines penetrating the lamina propria. Both also eroded the epithelial lining of the crypts and caused modest expansion of crypt diameter. Although the configuration of the mucosal surface may explain sites in which both species were able to attach, it does not explain their absence from other regions; histological sections and scanning electron microscopy showed the mucosal surface to be similar in configuration throughout the length of the spiral intestine. The cestode fauna of H. walga also included at least 1 species of rhinebothriine, 2 lecanicephalidean species, a trypanorhynch species, and 1-2 additional new species of Acanthobothrium. However, formal description of these species must await the collection of additional material, mature material, and/or the erection of the new genera. It is of note that the fauna of the dwarf whipray consists of a suite of unusually small taxa. Although the cestode genera reported here are generally consistent with those reported from other Himantura species, they are completely inconsistent with previous records from H. walga (as Trygon walga) in Sri Lanka. This suggests that either the original host identifications are suspect or that differences exist in the faunas of H. walga between these 2 localities.