THE GONADS OF MARGARITIFERA AURICULARIA (SPENGLER, 1793) AND M. MARGARITIFERA (LINNAEUS, 1758) (BIVALVIA: UNIONOIDEA).

A detailed study of the gonads of two endangered species ofthegenus Margaritifera living in the Iberian Peninsula, Margaritiferaauricularia (Spengler, 1793) and Margaritiferamargaritifera(Linnaeus 1758), based on macroscopic and histologicalobservationsis presented. In both species, gonadal tissue occurswithinthe visceral mass without a specific location. In hermaphroditespecimens,male and female acini are mixed in the visceral mass butcanbe clearly distinguished by detailed macroscopic study. Thegonadaltopography and cycle of Margaritifera auricularia is describedforthe first time, indicating that the species is a femalehermaphroditeand that gametogenesis occurs from December toMarch. Fiftypercent of Margaritifera margaritifera specimens studiedwerehermaphrodites and 50% females. (Received 6 March 2000; accepted 5 June 2000)