Ecology and Functional Significance of Uncoiling in Vermicularia Spirata: An Essay on Gastropod Form

In Bermudian waters, the uncoiling marine snail Vermicularia spirata cements itself to a variety of hard substrates, predominantly to the tree coral Oculina. Uncoiling has two major functions: rapid upgrowth to attain earlier access to the rain of detrital food particles, and flexibility in growth required for stable attachment. The branching Oculina is preferred because it provides numerous attachment sites along the course of upward growth. Snails attached to Oculina begin to uncoil earlier than those cemented to less advantageous substrates. Comparison of the uncoiled shell with a hypothetical coiled individual of equal shell growth provides an index of uncoiling. Snails attached to Oculina are more highly uncoiled than those attached to massive brain corals; snails attached to vertically oriented colonies of Oculina are more loosely coiled than those cemented to stubbier, horizontally branched colonies of Oculina; shells fastened to the bases of colonies of Oculina are more uncoiled than those attached near the tops of the same colonies. Although many Vermicularia are very loosely coiled, none approach the theoretical optimum of uncoiling (a straight tube after attachment). Although this is due partly to the necessity for growing around obstacles, the major constraint upon complete uncoiling is the inherited spiral mode of molluscan growth. Uncoiling is not random; Vermicularia always uncoils as a dextral spiral.