Butterflies of the Sea

Tiny. Ubiquitous. Vital. Delicate. Vulnerable. All these words describe pteropods (“wing-foot”). These marine snails are also called “sea butterflies” because of their winglike swimming appendages. Masses of pteropods drift with currents in the open ocean, where they provide food for fish and whales. Like garden snails, their earthbound relatives, pteropods build calcium carbonate shells. But pteropods’ thin, fragile shells may be vulnerable to the ocean’s changing chemistry. (Photo by Nancy Copley, Woods Hole Oceanographic Institution)