Archaenybelina gen. nov. (Trypanorhyncha Diesing, 1863) from Mobula thurstoni (Lloyd, 1908), including the description of two new species from Bali, Indonesia

Abstract Two specimens of Mobula thurstoni (Lloyd, 1908) were obtained from fishermen of Karangasem, Indonesia, and studied for trypanorhynch cestodes. Archaenybelina gen. nov., including two new species A. pseudotetrabothrialis sp. nov. and A. mimicricestus sp. nov., were recorded from the stomach and spiral valve and analysed for details of scolex and segment morphology, and surface ultrastructure. The new genus is characterized by 4 asymmetrical bothria separated by deep posterior notches, the presence of tegumental grooves, a homeoacanthous heteromorphous armature and a unique segment morphology. Both species can be separated by different hook sizes, basal hook rows and distribution of bothrial microtriches. Scolex surface ultrastructure shows hamulate spinitriches on bothria, lineate spinitriches along bothrial margins, and papilliform filitriches on the scolex peduncle. Similar microtriches have been reported from the bothrial margins of the Tentaculariidae. Tegumental grooves with a probably secretory function based on histology are present on the posterior bothrial margin. A collar of uncinate microtriches appear at the outer surface, separated from an internal bulbous structure, clearly distinguish this organ from the ciliated pits of the Otobothriidae. Based on four bothria, appearing not entirely separated at the anterior part of the scolex that indicates an originally bifossate state, a homeoacanthous heteromorphous armature, tegumental grooves, the absence of prebulbar organs and the presence of muscular rings, we assign the new genus into the Paranybeliniidae Schmidt, 1970. Describing first details of the segment morphology add to the family diagnosis in the most recent classification. The unique morphology of the new genus including its potential life cycle that involves oceanic devil rays as final and euphausiid crustaceans as second intermediate hosts are discussed.