Five new species of Acanthobothrium (Tetraphyllidea: Onchobothriidae) from the freshwater stingray Himantura chaophraya (Batoidea: Dasyatidae) in Malaysian Borneo.

Five new species of Acanthobothrium (Tetraphyllidea: Onchobothriidae) are described from the spiral intestine of the Freshwater whipray, Himantura chaophraya, in the Kinabatangan River in Malaysian Borneo. Based on criteria set forth in a previous categorization scheme for species of Acanthobothrium, these consist of 3 Category 1 species, Acanthobothrium asnihae n. sp., Acanthobothrium saliki n. sp., and Acanthobothrium zainali n. sp.; a Category 8 species, Acanthobothrium etini n. sp.; and a Category 2 species, Acanthobothrium masnihae n. sp.. Acanthobothrium asnihae n. sp. differs from all Category 1 species in its possession of a horizontal band of weak musculature that divides the posterior loculus in half. Among Category 1 species, A. saliki n. sp. differs from all but Acanthobothrium southwelli in its possession of postovarian testes. It differs from A. southwelli in its possession of fewer testes and a greater number of proglottids. Acanthobothrium zainali n. sp. differs from the 25 other Category 1 species in a combination of overall size, muscular pad and hook shape, arrangement and number of testes, ovary configuration in cross section, position of ovarian isthmus, and genital pore position. Acanthobothrium etini n. sp. is distinguished from all 5 other Category 8 species in its lack of testes from the proglottid antiporal and postporal regions and in testis number. Acanthobothrium masnihae n. sp. differs from the 35 other Category 2 species in its possession of fewer testes, postporal testes, or a greater number of proglottids. A key to Acanthobothrium species parasitizing H. chayophraya is presented. This represents the first report of Acanthobothrium from freshwater stingrays belonging to a family other than the Potamotrygonidae.