Embriogenic and Larval Development of Olivancillaria vesica auricularia (Lamarck, 1810) (Mollusca, Gastropoda, Olividae) in Laboratory Conditions.

Abstract

Egg capsules of Olivancillaria vesica auricularia collected in the surf zone of casino Beach, Rio Grande - RS, had been kept and observed in the laboratory. The capsules measure about 1.34mm in diameter. They were spherical, opaque-white in color and the adhesion base was wide. The capsules presented a circular pore on the dorso-lateral surface; and they usually adher to the bivalve shells. Inside of each capsule there was a egg, measuring 800um, rich in yolk inside an albuminous material. The embryonic development occurred in the interior of the capsule and lasts an average of 33 days. The egg had spiral segmentation, recognizing three main phases. In the last phase, a gastrula was formed, with the beginning of torsion. The pre-veliger, measured 1.100um and lasted 6 days, initiating the formation of the embryonic shell, the foot and the velum. In the veliger, which measured 1.380um, absorption of the yolk can be observed, as well as appearance of internal organs, and hardening of the transparent protoconch with the foot and the velum well-developed. The intracapsular animal measured 1.55mm and had an opaque protoconch. The absorption of the velum getting ready to hatch, happened on average after 10 days. The newborn measured about 1.8mm.