Sea Butterflies

I would like to share a natural encounter that I had on a recent family trip to Emerald Isle, NC. Our beach days were rudely interrupted by a marine swarm of tiny mollusks called sea butterflies. While swimming, we experienced numerous sharp, thorn-like pokes from what looked like little shards of glass! They stuck to our bathing suits and rash guards, keeping us out of the ocean for several days. My granddaughters decided that sea butterflies is too nice a name; instead, their new nickname was to be “annoying, pokey things.”

Sharp, pointy sea butterflies washed up on the beach at Emerald Isle, NC.
Sharp, pointy sea butterflies washed up on the beach at Emerald Isle, NC. They kept us out of the water for 3 days! (photo by A. Ewing)

Sea butterflies are planktonic marine gastropods in the order Pteropoda. (It’s hard to figure out the most accurate classification.) The sub order, Thecosomata, include the tiny snails that are mostly coiled or conical with transparent calcium carbonate shells. The “winged feet” of the pteropods have evolved into flaps that enable them to flit or swim through the sea. They can grow up to 1 cm in length and are very abundant in most of the world’s oceans. Another sub order of pteropods are referred to as sea angels. They lack shells and prey almost entirely on sea butterflies. Imagine the fierce ocean conflicts between butterflies and angels!
Pteropods are a vital part of the ocean food web. During our days at Emerald Isle when the “pokey” creatures kept us out of the ocean, we observed large schools of fish (possibly menhaden) feeding offshore. After four days of thorny seas, strong currents finally pushed the fascinating sea butterflies to another part of the coast.

A close-up view of various sea butterflies. (Internet photo)
A close-up view of various sea butterflies. (Internet photo)



For additional information about mollusks and related worldwide research, I highly recommend the book Spirals in Time: The Secret Life and Curious Afterlife of Seashells by Helen Scales (2015) and check out the following Internet resources:

Smithsonian magazine article: Amazing Sea Butterflies Are the Ocean’s Canary in the Coal Mine

Marine Species ID Portal: Species Identification – Styliolasubula