Surprise in a Small Package Foregut Metamorphosis in an Ectoparasitic Snail (Pyramidellidae)

Meeting Abstract

86-3  Sunday, Jan. 6 10:30 – 10:45  Surprise in a Small Package: Foregut Metamorphosis in an Ectoparasitic Snail (Pyramidellidae) HARMS, KS*; PAGE, LR; University of Victoria, BC, Canada; University of Victoria, BC, Canada

Members of the Pyramidellidae are tiny marine snails with highly unusual feeding habits relative to other heterobranch gastropods. They are described as ectoparasites because they feed on body fluids of much larger animals by extending an elongate proboscis, piercing the host’s skin with a stylet, and creating suction with a muscular bulb. Foregut anatomy of pyramidellids is so complex and modified that homologous relationships to foregut components of other heterobranch gastropods are difficult to recognize. However, correctly identifying homologs is a necessary first step toward reconstructing evolutionary changes to the foregut developmental program of pyramidellids. Many pyramidellids begin life as a veliger larva that feeds on phytoplankton using ciliated velar lobes and a larval digestive tract like those of other gastropod veligers. Our goal was to compare foregut development through metamorphosis in the pyramidellid Odostomia tenuisculpta with that of other gastropods to understand how the derived state of the foregut is generated during development. By examining thick and ultra-thin sections of larval and metamorphic stages, we conclude that the so-named acrembolic proboscis of this pyramidellid is actually an eversible oral tube and the piercing stylet is a single, highly modified radular tooth, rather than a jaw derivative as previously suggested. Surprisingly, except for the salivary glands and ducts, much of the highly complex, multi-component foregut of the post-metamorphic stage is constructed during a 4-5 day period of explosive metamorphic morphogenesis. This stands in marked contrast to predatory neogastropods, in which most components of the post-metamorphic feeding system become extensively differentiated in the larval stage prior to settlement and metamorphosis.

the Society for
Integrative &