Trypanorhynch cestodes of Mobula thurstoni (Lloyd) from Bali, Indonesia, including the description of Hemionchos arthanai sp. nov. (Cestoda: Eutetrarhynchidae Guiart, 1927).

Trypanorhynch cestodes were identified in the stomach and spiral valve of Mobula thurstoni (Lloyd) from Lombok Strait, Bali, Indonesia. This study includes the description of Hemionchos arthanaisp. nov. (Cestoda: Eutetrarhynchidae). New site and locality records were established for H. striatus Campbell and Beveridge, 2006, H. mobulae Campbell and Beveridge, 2006, Mobulocestus Campbell and Beveridge, 2006, Nybelinia balinensis Palm, Palm and Haseli, 2019, and Parachristianella campbelli Schaeffner and Marques, 2018. Hemionchos arthanaisp. nov. can be distinguished from the other Hemionchos species due to its smooth scolex surface lacking transverse annulations, the configuration of its five metabasal hooks per row where the hooks 1-4 (1´-4´) possess characteristic cavities, and its basal armature. The basal armature consists of two rows of enlarged uncinate hooks devoid of cavities, followed by three rows of slender uncinate to spiniform hooks without cavities, and three rows of conical, dorsoventrally flattened, falcate hooks with a strongly recurved mucronate tip. Although the life cycle of H. arthanaisp. nov. is unknown, euphausiaceans are expected to serve as intermediate hosts. This assumption is supported by the fact that H. mobulae has been detected in euphausiaceans, which are prey items for manta rays.