The ocellated eagle ray, Aetobatus ocellatus (Myliobatiformes: Myliobatidae), from Borneo and northern Australia as host of four new species of Hornellobothrium (Cestoda: Lecanicephalidea).

Four new species are described in the lecanicephalidean genus Hornellobothrium from the ocellated eagle ray, Aetobatus ocellatus, from Australia and Indonesian Borneo. The species possess flat, laterally expanded immature proglottids and a small internal, glandular apical organ diagnostic of the genus. To date, only 2 valid species are recognized in the genus: Hornellobothrium cobraformis Shipley & Hornell, 1906 , from " Aetobatus narinari " from Sri Lanka, and Hornellobothrium extensivum Jensen, 2005 , from A. ocellatus , also from Australia. The new species differ from H. cobraformis in the shape of the apical organ and mature proglottids, and from H. extensivum in testes number and scolex dimensions. The new species can be distinguished from one another based on the following combination of features: Hornellobothrium gerdaae n. sp. possesses testes arranged in 2 layers and lacks post-ovarian vitelline follicles; Hornellobothrium iotakotta n. sp. has a single column of 4 testes and lacks spiniform microtriches on the distal bothridial surface; both Hornellobothrium kolossakotta n. sp. and Hornellobothrium najaforme n. sp. possess a single column of 6 testes, but H. najaforme n. sp. is a longer worm with a greater number of laterally expanded immature proglottids. Host associations suggest this genus is potentially limited to A. ocellatus . While reports of up to 9 lecanicephalidean congeners in a single host species exist, they are considered dubious and in need of verification, mainly because of host identification issues. This study demonstrates the presence of at least 5 species of Hornellobothrium in A. ocellatus . Insufficient sampling of this host species across the Indo-Pacific and at each locality may account for the apparent restricted distribution of species of Hornellobothrium.