Nudibranch/Nematocyst interaction

Dear Annie,
I'm sorry I don't know how long nematocysts are retained in an aeolid's cnidosac. I guess it would depend on whether the aeolid had to use the ones it has, how often it feeds, its size etc. If anyone knows of a published study on nematocyst retention I would be interested.

Have a look at Cesar Megina's message about feeding in Hermissenda crassicornis, which shows it eats a lot of different animals. If you want to see how long it takes to replace its nematocysts, you will need to be able to identify nematocysts from different anemones and hydroids, so that you will be able to see when a changeover occurs. One possibility would be to feed them on a compound ascidian, which of course does not have nematocysts, and see if the aeolid loses the nematocysts in its cnidosac, and how long it takes. You could also try removing some of the cerata from Hermissenda and let them regrow while feeding on an ascidian, so that you know they won't have access to new nematocysts, then move them to a cnidarian food - sea anemone or hydroid, and see how long it takes for nematocysts to appear in the cnidosac.

With such a variable diet, Hermissenda crassicornis seems quite a good animal to use for some simple experiments.

Concerning your second question. I guess this is unrelated to the nematocyst question. Feeding preference experiments are difficult to interpret unless you know something about the biology of the food and the feeder. Navanax may prefer Phidiana crassicornis in laboratory experiments, but I would be surprised if they meet up with each other in the wild very often. So a laboratory preference may have no significance in understanding the biology and natural history of either the food or the feeder. As Cesar Megina mentions with Hermissenda crassicornis, in different places, Hermissenda eats quite different things. Usually in nature animals don't have the luxury of choosing their 'preferred' food. Food availability and competition from others, usually removes much choice from their list of possibilities.

Which doesn't really answer your question. I guess if you have to do a choice experiment you will have to find an animal with a fairly wide diet and let it choose. But trying to make sense of the results may be difficult.

Best wishes,
Bill Rudman.