Animals that aren’t as I expect them to be (such as flightless birds, legless lizards, flying fish) fascinate me. One such animal is the sea butterfly. A sea butterfly is as lovely as its name — it’s a delicate creature that flies on broad gossamer wings.
(You can get a quick look at it on this short YouTube video of a dive off the Monterey Harbor Breakwater.) But a sea butterfly isn’t what it seems. It’s not a butterfly, of course; neither is it a jellyfish. It’s a marine snail.

The sea butterfly (Corolla spectabilis) is a gelatinous snail adapted to a pelagic (open water) life. It’s not very big — the body core is about an inch (2.5 cm) and the wings grow to 3 inches (8 cm). They work like wings, flapping to move the animal through the water (as you saw on the video). Also on the video, you may have noticed a dark spot in the animal. That’s its gut. To eat, it creates a mucous sheet, like a drift net, up to 6.5 feet (2 meters) across to collect plankton from the water. This snail has no external shell, but is protected by an internal gelatin core called a pseudoconch (or faux shell) that’s covered with bumps called tubercules.

So why am I so interested in sea butterflies. It’s because of a beachcombing discovery. This week I found quite a few of these crystal-like jelly casings while I walked the beach. Unlike the usual jelly blobs, these glistened in the light, had more structure to them and were bumpy. Once I saw one, I continued to find sea butterfly pseudoconchs all along my walk.

Any jelly sea creature that’s washed onto the beach is pretty beat up. Waves can be rough. But lately ours have been gentle and a few of the beached sea butterflies still carried their wings.

It’s a shame to find their remains on the beach, but the discovery of these pseudoconchs has been a delight and they bring me just a little closer to the sea butterfly beauties that fly through the bay.

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Sources

A Blue Water News blog post helped me identify the pseudoconchs on the beach.

Sea Slug Forum: Corolla spectabilis

The JelliesZone: Corolla spectabilis

Wrobel, D. & Mills, C. (1998). Pacific Coast Pelagic Invertebrates: A guide to the common gelatinous animals. Monterey, CA: Sea Challengers and Monterey Bay Aquarium.