Return to the sea: Sagaratrema n. g. for the marine Liolopidae (Digenea: Diplostomida) with two new species parasitic in snakes from Sri Lanka.

The Liolopidae Dollfus, 1934 is a small family of digenetic trematodes with sexual adults parasitic in aquatic reptiles and amphibians. Liolopids exploiting snakes are constrained to Harmotrema Nicoll, 1914, but the genus includes species with presumably freshwater life cycles parasitic in terrestrial snakes as well as species with presumably marine life cycles parasitic in viviparous sea snakes and amphibious kraits. We hypothesize that this ecological distinction implies substantial separation in evolutionary history and propose Sagaratrema De Silva, Pathirana & Martin n. g. to accommodate the liolopids in marine snakes. Three species are delineated through an integrated approach, from novel collections of viviparous sea snakes in Sri Lanka, Sagaratrema rajapaksei De Silva, Pathirana & Martin n. sp., Sagaratrema rajakarunae De Silva, Pathirana & Martin n. sp. and Sagaratrema indicum (Chattapadhyaya, 1970) n. comb. (= H. indica) originally reported from India. Three other species known from marine snakes are transferred from Harmotrema to the new genus: S. laticaudae (Yamaguti, 1933) n. comb. (designated as the type-species), S. eugari (Tubangui & Masilungan, 1936) n. comb. and S. linguiforme (Wang, 1987) n. comb. (= H. linguiforme). The 3 species from Sri Lanka are similarly genetically distinct in sympatry as each is relative to S. laticaudae from Japan. Following these proposals, Harmotrema is revised and rendered monotypic for the type-species H. infecundum. Morphologically, Sagaratrema is distinguished from Harmotrema and other liolopid genera by the arrangement of the excretory vesicles, distribution of the vitellarium and size and shape of the body.