Abstract
Opisthobranch molluscs exhibit fascinating body plans associated with the evolution of shell loss in multiple lineages. Sea hares in particular are interesting because Aplysia californica is a well-studied model organism that offers a large suite of genetic tools. Bursatella leachii is a related tropical sea hare that lacks a shell as an adult and therefore lends itself to comparative analysis with A. californica. We have established an enhanced culturing procedure for B. leachii in husbandry that enabled the study of shell formation and loss in this lineage with respect to A. californica life staging.
Highlights
The Mollusca has been one of the most successful metazoan lineages in exploiting the advantages of the hard, calcified shell (Lowenstam & Weiner, 1989; Weiner & Dove, 2003)
Post-hatching larval development and shell growth The life cycle staging of B. leachii mentioned here is equivalent to the staging scheme that was described for Aplysia californica (Kriegstein, 1977) and currently in use at the University of Miami’s Aplysia hatchery (Rosenstiel School, 2012)
A. californica larvae grown at 22 ◦C and 25 ◦C showed that there was no difference in growth
Summary
The Mollusca has been one of the most successful metazoan lineages in exploiting the advantages of the hard, calcified shell (Lowenstam & Weiner, 1989; Weiner & Dove, 2003). There are several molluscan groups that subsequently evolved to have a highly reduced shell, e.g., squid, or have lost it completely, e.g., sea slugs (Kroger, Vinther & Fuchs, 2011; Morton, 1960). Within the sea slugs (Opisthobranchia), shell reduction or loss has occurred in members of the Cephalaspidea, Anaspidea, Sacoglossa, Acochilidiacea, Nudibranchia, and Pleurobranchia among others (Wagele & Klussmann-Kolb, 2005). These events support the notion that shell reduction or loss is not an isolated event and instead has evolved independently many times through parallel evolution (Gosliner, 1985; Gosliner, 1991). Shell loss paved the way for extraordinary body plan modifications observed in the different molluscan lineages that underwent this dramatic anatomical change enabling them to occupy new niches such as plastic sequestration from ingested macroalgae for photosymbiosis (Kempf, 1984; Rumpho, Summer & Manhart, 2000) in
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