Invertebrates in the Plankton: Mollusca
The molluscs, including gastropods, bivalves, cephalopods, and chitons, are the second largest of all invertebrate groups.  As adults, these animals have varied lifestyles, living in the water column, on rocky and sandy bottoms, within tidal flats and on rocky shores.  We observed several planktonic molluscs, described below.  For more information about the habitats of adult molluscs, see the other habitat pages.

This pedi-veliger larva is practially a juvenile clam.  Notice its well-developed shell.  Floating in the plankton, this animal consumes microscopic algae.  It will soon settle and grow to be a benthic adult.  In early stages of its development, this animal resembled the gastropod veliger below.


The Lacuna veliger swims freely in the plankton, using large ciliated lobes for locomotion and food capture.  At metamorphosis, the gastropod's body form changes dramatically.  The cilated lobes, larval heart, and part of the larval excretory system are lost when the animal assumes its bethic adult form.

Clione limacina, known commonly as a "sea butterfly," was one of the few completely pelagic adult gastropods we encountered in the plankton.   This pteropod, as it is classified taxonomically, is quite cosmopolitan in its distribution, ranging throughout the northern oceans.  Clione are relatively rare finds around Friday Harbor, though they are common to the north, in the Strait of Georgia.  The species has a planktonic veliger larva and a fascinating undulating swimming pattern.  To see the clione swim, check out this movie. Clione also has an unusual reproductive appendage that can extend out from the body and wrap around its partner.  This keeps the organisms linked together in the water current.

Plankton Home    Annelida    Arthropoda    Chaetognatha    Chordata    Cnidaria & Ctenophora    Echinodermata
Invertebrates 2000