We received several correct guesses. This is the zoea (free-swimming larval stage) of a Pelagic Red Crab (Pleuroncodes planipes)! The photo below shows the entire zoea:
We haven't been able to find many pictures of Pelagic Red Crab larvae, so we thought it would be fun to share a few. Eric also recorded some video (see below)!
Here's the basic sequence of events:
After finding live Pelagic Red Crabs on 24 January 2017, I was measuring them and counting the number of males and females. I discovered that several of the females were carrying eggs. Similar to lobsters, they brood their eggs attached to the underside of the abdomen (see below):
We wondered if the embryos would develop in Northern California waters. Based on a previous study that found they did well at 12°C, it seemed like they should develop and hatch in ~22 days.
Right on schedule, the embryos hatched today (after a minimum of 22 days)! This is what we saw when we came into the lab this morning — an adult female surrounded by hundreds of larvae, each ~2 mm long:
And here's a close-up of some of the larvae in the jar:
Carl Boyd described the larval stages of Pelagic Red Crabs in 1960. This drawing shows the first zoea:
Modified from Boyd, C.M. 1960. The larval stages of Pleuroncodes planipes Stimpson (Crustacea, Decapoda, Galatheidae). Biological Bulletin 118: 17-30.
And here's a close-up of a zoea in a similar position (shown in dorsal view, from above):
As mentioned, Eric took advantage of a rare opportunity to film some live Pelagic Red Crab larvae. You'll see the very active newly-hatched zoeae zipping around. (Among the swimming sequences and close-ups, watch for the rapidly beating heart.) Note: If you receive this via e-mail and can't see the video file below, click on the title of the post above to go directly to the web site.
I can't help showing a couple more pictures — two extreme close-ups. Check out the beautiful telson (last abdominal segment or "tail")...
...and the wonderful second antenna (the outermost antenna, adjacent to the eye):
We feel very fortunate to have observed and photographed these fascinating larvae. We hope you enjoy them, too!