EMBRYONIC AND LARVAL DEVELOPMENT OF ENSIS ARCUATUS (JEFFREYS, 1865) (BIVALVIA: PHARIDAE).

The razor clam Ensis arcuatus (Jeffreys, 1865) is distributed from Norway to Spain and along the British coast, where it lives buried in sand in low intertidal and subtidal areas. This work is the first study to research the embryology and larval development of this species of razor clam using light and scanning electron microscopy. A new method consisting in changing water levels using tide simulations with brief dry periods was developed to induce spawning in this species. The blastula was the first motile stage and in the gastrula stage the vitelline coat was lost. The shell field appeared in the late gastrula. The trochophore developed by about 19 hours post-fertilization (hpf) (19 ?C). At 30 hpf the D-shaped larvae presented a developed digestive system consisting of a mouth, a foregut, a digestive gland followed by an intestine and an anus. Larvae spontaneously settled after 20 days at 378 ?m in length.