A new genus and species of polyclad flatworm found in the mantle cavities of gastropod molluscs in the high-intertidal zone of the Pacific coast of Central America

Abstract

A commensal relationship is described between the polyclad flatworm Paraprostatum echinolittorinae Faubel & Sluys gen. et sp. nov. and gastropod molluscs living on the Pacific coast of central America. Although the worms are relatively large in comparison with their hosts, the latter sustained no apparent damage. Considering the fact that the molluscs live in the upper eulittoral zone and littoral fringe of the shore, it is unlikely that the polyclads could survive for long outside the hosts. Diagnostic characters for the new genus and species are a long penial stylet joined to the proximal vesicle and absence of Lang's vesicle. It is pointed out that Aprostatum clippertoni Bock, 1913 and A. longipenis (Kato, 1943) have been incorrectly transferred to the genus Euplana Girard, 1893 and that Discoplana malagensis Doignon, Artois & Deheyn, 2003 should be transferred to the genus Ilyella Faubel, 1983.