First description of the larvae of Dianthyrsus (Sabellariidae, Polychaeta)from the Gulf of California and Bahia de Banderas, Mexico

Larvae belonging to the family Sabellariidae (Polychaeta) were collected fr om the Gulf of California and in the Bahia de Banderas, on the west coast o f Mexico. The oldest stages were selected for identification. The presence of three parathoracic segments and one pair of opercular hooks led to the g enus Idanthyrsus. Identification at the species level was more difficult, a lthough I. armatopsis is a serious possibility. This is the first descripti on of the planktonic larval stage of a representative of the genus Idanthyr sus. The authors draw attention to the usefulness of a precise description of certain features, such as the morphology of uncini, or of the primary op ercular paleae. which simplifies the task of identifying larvae at the spec ies level. Comparison inside the family, between species whose development is known, confirms the homogeneous ontogenesis and suggests strong phyletic constraints. Then emerge the questions of reproduction for specimens livin g over a large bathymetric range and the origin of larvae collected in the open sea.