Sea butterflies

Sea Butterfly Pseudoconch1 by CM ParsonsAnimals 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.

Sea Butterfly Pseudoconch2 by CM ParsonsSo 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.

SeaButterfly on Beach by CM Parsons

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.

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.

10 Comments on “Sea butterflies

  1. Beautiful photos! I found one of these yesterday (thought it was a salp at first) and your post helped me correctly ID it.


    • The sea butterfly appears about 30 seconds into the video (right after the shot of the diver) and, as you describe, is filmy and flapping like a bat ray. Unfortunately, the view is very short. Chris


  2. Fantastic video. There is so much in there. Nice views of feeding giant barnacles (right?) are impressive. I’ve seen a few tests washed up on shore but never the live version. Thanks.


    • There is a lot in such a short video, including the feathery feet of the feeding barnacles you mention. I like the decorator crab covered in algae and the bed of sand dollars at the end. But the sea butterfly is special. That area is a favorite local dive spot.



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