Intrigued? Meet Janthina umbilicata, also known as a Purple Sea Snail. Eric and I were surprised to find hundreds of them washed ashore on Salmon Creek Beach yesterday (19 January 2016). [There were likely thousands on the entire beach.]
Janthina is a pelagic snail, spending all of its time in the open ocean (unless it is washed onto beaches during storms). It's also important to know that Janthina is primarily tropical/subtropical. They're not often seen this far north, and it's likely their appearance here this winter is due to El Niño conditions.
Here's what they looked like on the beach — one photo with a blade of giant kelp for scale, and another with a ruler.
Note the range in the size of the snails. The overall range was from about 0.5 mm long to about 7-8 mm long. Here's an example of the different sizes we found:
I have a fun connection with Janthina. I grew up on a barrier beach (in Massachusetts), and when I was young, I would scan the pages of the field guides in our house, especially the identification guide for shells. I always paused on the page about Purple Sea Snails because I was so taken with their amazing color and I wondered if I would ever get to see one. I didn't until 2005, my first year in California (when I found a few empty shells washed up on the beach.) It has now been 11 years, but I never imagined I would see hundreds of them — and that some of them would be alive!
The next picture displays their wonderful color and the striations on the shell:
Because Janthina is rare in northern California, we brought some snails into the lab for documentation. Once in the water, the snails started actively rebuilding their floats!
Janthina drifts at the surface of the sea, suspended from a raft of bubbles that they create. The process was easy to observe, and you're in luck, because Eric filmed it (video below).
Remember that the view you're seeing is from above; that is, you're looking down at the snail hanging below its float. You'll see the snail's tentacles — each tentacle is branched, and has a black line of pigment. The foot is black and very active.
Watch for a few different things. The snail extends its foot and breaks the surface. The front of the foot expands and a concavity is formed in the center, allowing the snail to trap a bubble of air. The snail then attaches the bubble to its float with mucus. It also appears to spend time running its foot over the surface of the raft, perhaps to ensure that all of the bubbles are cemented together.
We hope you enjoy the video!
We heard a rumor that Janthina was also observed in Bolinas. Have you found them anywhere? It would be great to keep track of their occurrence in northern California (and farther north?) this year.