Reproduction in Flabellina iodinea

Dear Jennifer,
I don't know why you call yourself 'hopeless' - after all you did find the Sea Slug Forum! I didn't know there were any websites explaining the life cycle of Flabellina iodinea. I wouldn't mind a reference to the sites please. As far as I know the only reference is Engel's thesis (1976) which is listed at the top of the page. I guess you would have to go to Santa Barbara to look at it. All I know is that they lay eggs [see photos in Mike Miller's message] and the eggs take about a week to hatch as free-swimming veliger larvae which live in the plankton, feeding on phytoplankton (microscopic plants), before settling on to the sea bottom and turning into miniature slugs. I don't know how long they last in the plankton.

Now to the rest of your question. You ask if both sexes become pregnant. Firstly mammals are the only animals that really become pregnant, because 'being pregnant' basically means growing an embryo or carrying a baby inside your body. With few exceptions, only mammals do that. Some other animals become enlarged as large numbers of unfertilised eggs develop inside them. They may look pregnant but a better term for them is probably 'gravid'. However nudibranchs don't fit into either category. They are hermaphrodite which means they have a fully functioning set of male and female reproductive organs. This means they all produce eggs and sperm, and so can act as both male and females. The one thing we think they can't do is fertilise their own eggs.

I hope that answers your questions
Best wishes,
Bill Rudman