Dear Gonçalo,
If you haven't looked at the List of the Worldwide Food Habits of Nudibranchs - by Gary R. McDonald & James W. Nybakken, its a good place to start.

I would also welcome more recent feeding data.
Best wishes,
Bill Rudman

Dear Michael,
I think they are just plain lost. Both are sponge feeders. Mind you nothing is too strange for molluscs. There are species of colubrariid and marginellid snails which wait for Parrot Fish to form their 'nests' to sleep in at night and then feed on them by piercing soft parts like around the eyes. I think there are also cancellarid snails which do similar things to rays. And of course there is always Gymnodoris nigricolor which lives on gobies.

So although I think they are lost, it always pays to keep an open mind about such things.
Best wishes,
Bill Rudman

Dear Chiara,
Aeolid nudibranchs of the Family Aeolidiidae are all specialist feeders on sea anemones and their close relatives the zoanthids. Here is a list of the species on the Forum. Check through them for information on feeding.

Dear Andrea,
The short answer is I don't think they do like algae that much and I am sure they don't eat it. You certainly see nudibranchs on algae - perhaps because they stand out against the rather uniform background colour of the plant - but seeing them there doesn't mean that most of them are on algae. All it measn is that most of the ones you are seeing are on algae. prehaps most of the population are well camouflaged on their food, or in crevices etc etc.

Why are they on algae at all? Both cheromodorids and phyllidiids are sponge feeders so I presume that if you find them on algae its because they have crawled there. Although I love them dearly, I must admit that they are creatures of little brain. They search for their food by sensing chemicals in the water. Unless they have a good scent to follow I presume their movement is rather undirected, so if they crawl up the stalk of a seaweed the chances are quite high that they will stay on the plant for some time. On the other hand there are many nudibranchs which feed on hydroids and bryozoans that grow on algae. These nudibranchs, including some aeolids, dendronotoideans and polycerids, are therefore commonly found on algae. Althopugh they may seem to be grazing on the algae they are in fact grazing on some epiphytic animal colony growing on the algae.
Best wishes,
Bill Rudman

Dear Ben,
Have a look at the other questions on this page, below your message. My comments there will give you plenty of information. I'm afraid there is a mistake in your email address so I can't let you know about this answer.
Best wishes,
Bill Rudman

Dear William,
You want this information before Monday? You are very lucky that I am feeling kind! If you want to find information on the Forum click on anything underlined and use the navigation buttons at the top and bottom of every page.

There is a page on the Forum called 'Predation Records - Who eats Sea Slugs?'. If you go there you will find some examples of things that eat sea slugs. If you want more general information go to the General Topics List.

On your question about what they eat. Have a look at the top of this page for advice. Also have a look below your message for similar questions I have answered before.
Good Luck with your project - but next time don't leave it to the last minute
Bill Rudman

Dear Anna,
Nudibranchs are all carnivorous, each species usually having a very specialised diet, eating only one or a few items of prey. Some other sea slugs, such as the Sea Hares, are herbivores, feeding on different types of sea weed.

Have a look at the messages below yours on the Feeding Page for some background information and some suggested places to look.

It would also pay to look at the General Topics Index for other pages which may be of interest. As I say in most of the messages use the SEARCH BUTTON as well. If you type in food or feeding you will many more examples.
Best wishes

Dear Phanor,
I think you can be fairly safe in assuming that an aeolid that eats opisthobranch eggs is most probably a member of the genus Favorinus. However the only way to be sure is to have a look at their anatomy, and in particular the single row of radular teeth.
Best wishes,
Bill Rudman.

Dear Eddie,
'Please help asap' requests usually suggest you've left an assignment to the last minute. Let's hope you make it - but I'm afraid I can't drop everything to meet your deadline.

Most of the species you mention are in the Forum so go to the relevant page and look at the attached messages for the information you are after.

A good source of information on nudibranch diets is Gary McDonald & James Nybakken's A List of the Worldwide Food Habits of Nudibranchs.

best wishes,
Bill Rudman.

Dr Rhanor Gillette's lab has two movies of opisthobranch feeding behaviour. One is of Pleurobranchaea learning to avoid a cnidosac-wielding Flabellina and the other is of Navanax inermis feeding on an aeolid. This shows that like the aglajid genera Melanochlamys and Chelidonura it feeds by using the buccal bulb as a suction pump.

Although the two mpg files may take a while to download they are worth persevering with.
Bill Rudman.

Dear Sheila,
Sea Slugs have a wide variety of diets, and most species are very specialised, eating only one or a few items of food.

Some, such as the Sea Hares are herbivores, eating sea weeds. Others such as the nudibranchs are specialised carnivores, each species feeding on a particular food. If you look around the Sea Slug Forum you will find some photos of different Sea Slugs and their food. A few examples of nudibranchs feeding are:
Glaucus atlanticus which feeds on the floating cnidarian Physalia,
Gymnodoris subflava, which feeds on other nudibranchs,
Favorinus japonica, which feeds on other Sea Slug eggs, and
Jorunna sp., which is one of many dorid nudibranchs that feed on particular sponges.

Another group of herbivores are the sacoglossans which feed by sucking the contents out of individual cells.

If you look at the yellow bar at the top of your message you will see a SEARCH button. If you type in 'food' or 'feeding', you will get a list of pages in the Forum which are about the food of different species.

Concerning your second question about the advantages of having or not having a backbone. One is not better than the other, they are different. Many invertebrates have an outer shell or exoskeleton which gives them support and protection and others like worms and slugs use their blood or other body fluids to give them a hydrostatic skeleton. I'm afraid the question is a bit too big to answer here. Just remember that invertebrates make up 99% of the animal Kingdom so it is obviously a very successful body plan.

Best wishes,
Bill Rudman.