Wildlife of the Day (Episode 3)

Pteropod shells Hugh retrieved from tonight's box core.

We've found shells like these on the surface of almost every one of our box cores on this cruise. Hugh picked these out of tonight's box core and wanted to know about them. I hope this answers his questions.

They are pteropods -- little marine crustaceans with translucent shells that are also known as a sea butterflies or flapping snails.

These planktonic gastropods (snails) are found in all oceans, from the Arctic to the tropics. They spend their lives floating and swimming, and can being carried along in ocean currents.

The name pteropod is an old one, but it is still commonly used. In Greek, pteros means "wing" and podos means "foot," making the old word an excellent description for this animal that swims by using two wing-like appendages.

Pteropod shells are made of aragonite. They are thin and delicate, and are easily dissolved in the deep ocean. In the Atlantic, the aragonite compensation depth (the ACD -- the depth at which mineral aragonite dissolves) various with location, but is generally between 2000 to 3000 meters. This core was taken at a depth of 2372 m -- obviously above the local ACD.

Most pteropods live in the upper 500 m of tropical and subtropical waters. They are nocturnal filter-feeders, descending to deeper water in the daylight hours and rising to the surface waters at night to feed on microscopic organisms.

Here's a little know fact: pteropods start life as males and then become females. Interesting . . .


Living pteropods