Opisthobranchs in the Suborder Euthecosomata, which includes the cavoliniids, all have a calcareous shell.  Cavolinia tridentata is no exception, possessing a globose shell, length to 1 cm with 3 distinctive posterior projections.  Large ciliated mantle extensions (absent in the photo) pass through slits in the shell.  They function to increase buoyancy and stability, and are covered with cilia that produce water currents.  The shell and a transparent gelatinous pseudoconch are enclosed by lobes of the mantle.  Most of the body and the swimming wings have a light brown color.  A large mucous feeding web (diameter from 10 to 20 cm) is used to collect tiny planktonic organisms, including bacteria, small crustaceans, gastropod larvae, dinoflagellates and diatoms.  The web is collapsed into a string and eaten with the bounty of food; a fresh one is quickly deployed.  Cavolinia favors warm oceanic water and occasionally ranges as far north as southern and central California.  

All photographs © David Wrobel and may not be used or copied without permission!