The marine gastropods and bivalves go through a larval stage called a veliger. This larva gets its name from the ciliated structure, called a velum, that the animal uses for swimming. Veligers have shells–1 for gastropods and 2 for bivalves–and can withdraw the velum into the shell. Even gastropods that lack shells as adults, such as nudibranchs, have shells as larvae.
The egg mass from Dendronotus is still intact and the embryos are developing nicely. This morning when I looked at it through the microscope I could see the little larvae swimming around inside their egg capsules. I wanted to take a closer look under the compound scope, and when I teased apart the egg mass some of the larvae were forced to “hatch” prematurely. They’re not yet ready for life on their own but now they’re out in the real world swimming, for better or for worse.
Not being one to let an opportunity like this go to waste, I took some video of the almost-veligers.
You can see the cilia on their little velums whirling around. The larvae aren’t as spherical as I had expected, based on what I’ve seen in other nudibranchs, and I think it’ll be fun seeing how they develop. More as things unfold!
The natural world, seen through your perceptive and well-trained eyes, is a beautiful thing. Thanks for sharing, Allison!
My second-ever encounter with marine inverts was looking at predation on Onchidella veligers up at Friday Harbor. Someone had the idea that veligers could survive ingestion by tunicates by pulling up in their shells and later getting ejected as pseudofeces. Whoever suggested this clearly hadn’t thought much about it — there’s no way veligers can get out of all the snot that they get embedded in during the process.
My first-ever encounter? Also at FHL, during the same course — Membranipora membranacea settlement. That one actually got published.
Julie–Thanks for the kind words! I find your written essays to be inspiring.
Andy–Yeah, I remember reading that veligers survive getting eaten by closing up and passing through guts intact. Isn’t that one of the arguments for the evolution of torsion–the ability to pull the foot and velum inside and close up the operculum?