Nudibranch Egg Development

When the nudibranch in my tidal pool jar began laying eggs on the surface of the water and elsewhere in the tank, there was some question about whether they would be viable. I saw in a few of the eggs what I took to be cell division, as in the shot below where we can see some of the eggs have clearly divided middles (see the middle, bottom row).

Cell Division

Signs like these seemed like they might simply be wishful thinking on my part, though. The nudibranch floating around the tank is alone, and while they are hermaphroditic, they can’t self fertilize. Without another nudibranch to offer up genetic material, these eggs would be inviable. At the very least, I supposed I could take the opportunity to take some nice high mag shots of the eggs, which I have. They offer a view of the cell, it’s nucleus, the granular qualities of the cytoplasm.

Egg High Mag 6

Several days into watching the cells, I noticed some hopeful signs, though. The inside of one egg was now spinning. Then it was not just one, but several eggs who were spinning.

Here it is in high magnification.

Nudibranches hatch as veligers, like many other snails. Which explains the rotating motion in the cell. They’ve reached the point when cilia have formed, but aren’t yet at the point where they can hatch. You can tell from both of these that the larva isn’t formed yet. It’s still attached to a yolk, still a not quite formed life. But it has locomotion and the ability to move around in its small womb. If it were a mammal, we’d say it was kicking (though, if it were a mammal, it wouldn’t have cilia).

These were hopeful moments for me, so I’ve kept my eyes peeled for the hatchlings. Finally, last week, I caught some.

You can see their shells, of course, but notably, you can also see statocysts peering out at you like eyes. In this shot, the effect of the cilia beating on the surrounding water is evident, as microscopic particles get caught in the current.

Here is a pair caught up with each other.

I’m going to monitor the tank in coming days/weeks for their more adult phases. I assume that some will die, that others will be consumed by their siblings. But some will live, which is an exciting prospect. The question remains of how the adult nudibranch was fertilized in the first place. Was it fertilized before I caught it and then carried the eggs until it was time to lay them (there have been several broods at this point). Do nudibranchs, like some other species, carry the sperm of their partners around with them to slow release at intervals? I don’t know. For now, I am only excited–perhaps inordinately so–at the prospect of seeing some tiny nudibranch action in my lens.




6 Comments Add yours

  1. Saad bhamla says:

    This is super cool Matt.
    Im curious to see the tank where you are cultivating the organisms.
    When I found nudibranch eggs last time, the were connected in a viscoelastic matrix. Are you cutting the eggs out for each individual video??

    Really well done on the post. 🙂 I enjoyed reading it as always


  2. Manu says:

    @Matt: incredible mystery you have found in your hand. How could they possibly be fertilized – unless either the water you collected already had floating gametes or the fact that a storage of gametes of both sexes exist somewhere.. Phenomenal..

    Also – me, Marie and Tom will babe posting a post soon on how to use items from the kitchen to actually visualize fluid flow in organisms. I am half way through my first list of materials and we have one good candidate – corn starch. These are microscopic particles that can be seeded in the slide to visualize fluid flow. More on this will follow soon 🙂


  3. Matt.Rossi says:

    @Saad In the video you posted, the viscosity of the fluid around the eggs seemed to have roughly the viscosity of runny egg whites. This nudibranch drops her eggs in more of a firm gel, consistent with the texture of other snail eggs I’ve seen. They’re usually laid at the surface of the water, and they come in a thin spiral. When I image them, I gather up the full egg group and place them in a well slide with the slip cover raised on blue wall putty. There’s enough play in the eggs that I can adjust focus and not worry about crushing them.

    I’m actually on a long-term mission to try to catch the full development of one of the eggs from laying to hatching. This would involve a long-term timelapse shot of them. Not the easiest to get, but I think it’s doable. My main problem so far has been to find a container thin enough that the lens can get a sharp focus on the egg while also holding enough water that it won’t evaporate or run out of oxygen.

  4. Matt.Rossi says:

    @manu there’s another possibility that I hadn’t considered, which is that this isn’t a nudibranch but some other variety of snail that can self-fertilize.

  5. laksiyer says:

    @Matt. Brilliant post. The spiral cleavage of the embryo is really nice. Nudibranchs fertilize internally. Usually they do not self-fertilize.

  6. Cristina Bosch says:

    Amazing post! Your videos and findings are superb!!!!

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