REPRODUCTIVE-BIOLOGY OF THE SESSILE GASTROPOD VERMICULARIA-SPIRATA (CERITHIOIDEA, TURRITELLIDAE)

The reproductive and developmental biology of the sessile gastropod Vermicularia spirata (Philippi, 1836), collected from the Florida Keys, was studied from living and preserved material. Individuals of this species attach themselves to a variety of substrata, but were mainly found embedded in the white sponge Geodia gibberosa. Pallial reproductive structures of both sexes of V. spirata were found greatly to resemble those of Turritella communis, a free-living member of the same family. In both species, animals of both sexes have open pallial ducts formed by two wide, recurved laminae. In the female of V. spirata, the laminae of the pallial oviduct serve as a capsule gland; a pair of side pockets represent a fertilization pouch (possibly doubling as a copulatory bursa) and a seminal receptacle. The functional significance of the extensive, open, pallial sperm duct is not yet clear. Vermicularia spirata is a protandrous hermaphrodite, and small males are free-living; they become attached at about the time they undergo sex reversal. Fertilization is probably brought about by males crawling close to the apertures of the large, sessile females before releasing sperm. Egg capsules are brooded in the females' mantle cavities. Ova of about 300 μm diameter give rise to large (about 600 μm long) swimming-crawling veliger larvae with shells of two and a half whorls. The veligers are capable of metamorphosis at the time of hatching, but siblings from one brood metamorphosed over a two-week period in the laboratory. Juvenile snails grew rapidly by filtering phytoplankton added to their culture water. The life history of V. spirata is well adapted to assure fertilization and recruitment in a species otherwise committed to a sessile, filter-feeding existence. © 1990 The Malacological Society of London.