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

The reproductive and developmental biology of the sessile gastropodVermicularia spirata (Philippi, 1836), collected from the FloridaKeys, was studied from living and preserved material. Individualsof 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. spiratawere found greatly to resemble those of Turritella communis,a free-living member of the same family. In both species, animalsof both sexes have open pallial ducts formed by two wide, recurvedlaminae. In the female of V. spirata, the laminae of the pallialoviduct serve as a capsule gland; a pair of side pockets representa fertilization pouch (possibly doubling as a copulatory bursa)and a seminal receptacle. The functional significance of theextensive, open, pallial sperm duct is not yet clear. Vermiculariaspirata is a protandrous hermaphrodite, and small males arefree-living; they become attached at about the time they undergosex reversal. Fertilization is probably brought about by malescrawling close to the apertures of the large, sessile femalesbefore releasing sperm. Egg capsules are brooded in the females'mantle cavities. Ova of about 300 µm diameter give riseto large (about 600 µm long) swimming-crawling veligerlarvae with shells of two and a half whorls. The veligers arecapable of metamorphosis at the time of hatching, but siblingsfrom one brood metamorphosed over a two-week period in the laboratory.Juvenile snails grew rapidly by filtering phytoplankton addedto their culture water. The life history of V. spirata is welladapted to assure fertilization and recruitment in a speciesotherwise committed to a sessile, filter-feeding existence. (Received 3 February 1989; accepted 19 April 1989)