The Mollusc Module

Molluscs—derived from the latin word for soft—make up the second most speciose animal phylum (after arthropods), and are bilaterally-symmetric, unsegmented members of the protostome (lophotrochozoan) superclade, the Spiralia.  Molluscs have adapted to virtually every habitat on earth (save for the sky, as there are no flying forms), and exhibit a stunning array of morphological, physiological, and behavioral diversity.  Members include the bivalves (oysters and mussels), chitons, gastropods (snails and limpets), and cephalopods (octopus, cuttlefish and squids).  Although they form a monophyletic group, few synapomorphies define the entire group; one highly conserved feature is the mantle, an organ in the dorsal body wall that secretes biominerals in shelled forms.  Molluscs have been employed for over 100 years in the study of developmental mechanisms, cell biology, population genetics, materials sciences, neurobiology, behavior, physiology, evolution, and aquaculture.  So far, two Nobel prizes have been awarded for discoveries made using molluscs: the 1963 Nobel Prize in Physiology or Medicine for uncovering the ionic mechanism of action potentials using the giant squid axon, and the 2000 Nobel Prize for Physiology or Medicine for discoveries concerning signal transduction in the nervous system using the gastropod sea hare Aplysia.  Recently, CRISPR/Cas9 has been successfully used to knock in a fluorescent transgenic reporter using the gastropod snail Crepidula, the first demonstration of this approach in any lophotrochozoan. 

Some of the earliest developmental studies using molluscs were carried out in the late 19th century by E.G. Conklin working at the MBL with slipper snails, including Crepidula fornicata.  Since Conklin’s seminal work, mollusc embryos have been used to study cell lineage, spiralian fate maps, asymmetric cell division, sub-cellular localization of mRNAs, organizer signaling, chirality at the levels of cells and organs, evolution of biomineralization, and the formation of the nervous system, to name a few.  The spiral cleavage program is ancestral for molluscs (notably lost in the cephalopods) and provides a powerful framework for comparing developmental mechanisms among morphologically diverse molluscan species, and even between molluscs and other phyla like annelids and nemerteans that share this highly conserved mode of development (as members of the Spiralia/Lophotrochozoa).

In this module students will have access to a variety of molluscan embryos that can be used for cell lineage tracing, embryological manipulations, laser ablation, gene-perturbation, immunohistochemistry, and live imaging using fluorescently tagged bio-sensors.  You will also have access to the larvae and adults of several closely-related species (such as the slipper snails) that exhibit different modes of development, including direct (lecithotrophic) versus indirect (planktotrophic) development.  Students will also be able to study the formation and regeneration of the shell.