The Dendronotus veligers are still alive. I've been running into the same difficulties I've always had when trying to rear nudibranch larvae: hydrophobic shells that tend to get stuck in the surface tension of the water. Larvae that are trapped at the surface can neither swim nor feed.
We can pretty easily rear sea urchin larvae in culture by stirring jars on a paddle table. The stirring keeps the larvae and their food in suspension; without stirring the larvae would settle on the bottom and die. Nudibranch veligers are stronger and faster swimmers than sea urchin larvae and I thought I could get away with not stirring them, as I worried that the paddles might break the larval shells.
Two jars of larvae are being stirred on the paddle table, along with several jars of sea urchin juveniles that resulted from a spawning I did back in late February. The paddles move back and forth and keep the water moving, ensuring that the larvae have pretty consistent access to food.
It's a little early to tell, but it seems that there may be fewer larvae trapped at the surface in these jars. And I didn't see more smashed or broken larvae in these jars compared to the others. I'll look at them again tomorrow to reassess.
One jar of larvae is being gently bubbled, to see if this helps break the surface tension. I started with bubbling that was too gentle, and the other day upped the airflow a bit. There is a slow circular current in the jar that might be helping.
The two beakers in the front of this table have no agitation at all. These larvae are dependent on oxygen dissolving into the water from the surface, and I'm a little worried that they might be a little oxygen-stressed. They are definitely getting stuck at the surface, so I doubt this will be a long-term solution to that particular problem.
Tomorrow I will change the water in all the jars and beakers, and try to assess the amount of stuckage in each. Hopefully either stirring or bubbling will be the way to maximize survival of my larvae.