Meeting Abstract

31.3  Tuesday, Jan. 5  Cone snail metamorphosis: differentiation of the venom apparatus from the foregut of the planktotrophic larva. PAGE, L.R.; University of Victoria lpage@uvic.ca

Highly derived adult gastropods with complex life cycles, such as members of the genus Conus, have circumvented potential constraints of larval functional needs to achieve post-metamorphic specialization of the adult feeding apparatus. The radular teeth of cone snails are hollow harpoons, impaled into prey by a proboscis, that deliver a cocktail of immobilizing neuromuscular toxins elaborated by a venom gland. I reared larvae of Conus lividus through metamorphosis and cut histological sections through developmental stages to determine how this highly derived adult morphology is built within the body of the phytoplanktivorous larva. Results showed that the post-metamorphic venom gland differentiates as a channel of secretory cells along the ventral wall of the larval mid-esophagus. Within 48 hours after the onset of metamorphosis, this ventral channel of secretory cells peels away from the mid-esophageal wall; the separated tube of epithelium is the definitive venom gland that remains attached to the esophagus by a very narrow connection immediately posterior to the radular sac. The muscular bulb of the venom gland forms by 4 days after the onset of metamorphosis. Metamorphosis also involves total destruction of the distal larval esophagus and mouth. The buccal tube that extends down the post-metamorphic proboscis forms during metamorphosis by rapid proliferation and expansion of a nest of cells embedded within the ventral wall of the larval foregut, anterior to the radular sac. Comparison of events of foregut metamorphosis in Conus lividus and the buccinid gastropod, Nassarius mendicus, provides a developmental explanation for differences in the position of the radular sac relative to the probosicis in these two neogastropods.