| The pre-torsional veliger, with a well-developed velum, was noted between 17 and 22 hrs after fertilization. The propodium was large, and the larval shell had a distinct whorl. The velum was round and single-lobed, resembling that of a bivalve veliger. As the velum developed, the green pigment aggregated around the outside of the velum in large, elliptical spots with the smaller dots still present in the prevelar area. The turquoise pigment was concentrated in the digestive gland area and indicated the larva's yolk supply. At 23 to 26 hrs after fertilization the larval shell was complete, having one complete whorl, measuring 0.27 to 0.28 mm at its greatest width. The operculum was well-formed, the mantle cavity evident and the larva could withdraw completely into the shell. Two tiny black eye spots were apparent on the prevelar area, and torsion was complete. The velum of the veliger gradually became bilobed between 24 to 48 hrs after fertilization and was accentuated by two rings of green chromatophores, but it remained small. The eye spots became larger and more distinct, and the foot became noticeably larger. Between 48 and 72 hrs after fertilization, the velum had distinct, dark green "rims" on the outer side of each lobe, and small protuberances of the tentacles were evident near the eye spots. The lecithotrophic larvae search for the substratum with their foot, now ciliated, outstretched. Sixty hours after fertilization, many larvae were crawling, with the twirling velum protruding from beneath the larval shell opening. Larvae altemated between swimming and crawling during this
period. At about 3 days, the foot became very sticky, and the larvae could attach quickly to a substratum. |