Larval development of theterebellid polychaete Eupolymnia nebulosa (Montagu) in the Mediterranean Sea

The morphology of young stages of Eupolymnia nebulosa (Montagu, 1818) is observed using SEM. Significant changes occur at several times after egg laying. The transition from endotrophy to exotrophy takes place when the larvae are about 13–15 days old. At the same time, the primary tentacle appears as a hemispherical bud; the first setae to emerge are transitory and club-shaped. They are shed when the larvae are about 50 days old. Observations on the development of the uncinigerous torus of the 11th segment (the first one bearing uncini with the main fang in an alternated direction) indicate that the uncini appear at the dorsal extremity of the torus and then move toward the medio-ventral axis as they increase in size. The uncini are shed when they reach the ventral extremity of the torus. These changes may result in taxonomic confusions unless the complete sequence of development is known.