Dear Ian,
Thanks for the rapid response. Looking at your photos makes me wonder whether it is the same as the south-eastern Australian species, but hopefully Cynthia Trowbridge and others working on this complex of species will put us out of our misery soon. Sherman Bleakney (1989) decided Placida dendritica was a worldwide species but more recent work suggests there are a number of distinct regional species. If this proves true then the New Zealand animal, and perhaps its southeastern Australian look-alike, will revert to the old name Placida aoteana (Powell, 1937).

Smaller animals in Sydney look much like your photos, but as they grow they tend to become broader in the body with more flattened cerata.

• Bleakney, J.S. (1989) Morphological variation in the radula of Placida dendritica (Alder & Hancock, 1843) (Opisthobranchia: Ascoglossa/Sacoglossa) from Atlantic and Pacific populations. The Veliger, 32: 171-181.

Best wishes,
Bill Rudman

Dear Ruth,
You have certainly found a beautiful spot to work - and visit. When I was there many years a ago as a student, the lab was much more rudimentary.

Both the sacoglossans you mention feed mainly on an alga we used to know as Codium dichotomum, though I can't be certain that is still it species name. The important thing is that the alga, although usually intertidal, is usually found in crevices or under the brown alga Hormosira banksii [Venus's Necklace] - somewhere damp rather than immersed in a pool. Since its out of water at low tide, the sacoglossans are very difficult to see because they are lying flaccid on the algae. Often the first clue to their presence are their egg masses. The other way is to bring clumps of Codium back to the lab and cover them with sea water and watch for crawling slugs. I can't recall from memory whether the Codium is found on the rock platform at the lab, but it is certainly present in some of the nearby inlets and protected local shores. I am afraid you will need to get advice from local experts on the whereabouts of the Codium, because that is the key to finding the slugs. If you have not yet found this alga, there are some photos on the Fact Sheet and in some of the messages about this species. They are close-ups, but it is the only green algae you will see that looks like a branched finger sponge.

One word of caution however. Although both these slugs are relatively common, I'm afraid sea slugs are hopelessly unreliable. There is no guarantee that even the most common species will be there when you need it.

Good luck with your project,
Best wishes,
Bill Rudman

Dear Trevor,
Although this looks quite like an aeolid nudibranch it is in fact a sacoglossan. While both are 'sea slugs', sacoglossans are herbivores while all nudibranchs are carnivores. With few exceptions, sacoglossans feed by piercing the cell wall of particular algae [sea weeds] and sucking out the cell contents. In some species, like this one, the green chloroplasts from the plant are retained alive in the animal's digestive system, where they continue to photosynthesise, providing a plant-like solar powered way of life for the slug. The green specks and network in the body are microscopic branches of the difetive system where the chloroplasts are stored. It is an interesting coincidence that today I am also posting a message on a solar-powered nudibranch [#16890 ] which has a quite different approach to solar-powered life.

At present we can't give you a good name for this species, as there are similar-looking species all around the world which are still being studied to determine just how many species there are. At present we are just calling it Placida cf. dendritica

Best wishes,
Bill Rudman

Thanks Rachel,
There seems to be no better camouflage than to colour yourselves with the chloroplasts directly from the algae your sitting and feeding on. This and Elysia maoria, whose egg you illustrated in your last message are the two common feeders on this Codium in New South Wales, so its nice to see the differences in their egg ribbons. This is the ribbon I have always assoiated with Placida cf dendritica so its nice to have it confirmed.
Best wishes,
Bill Rudman

Dear Nishina,
This is most probably a species of Placida but not P. cremoniana. I think this is probably the Japanese 'form' of Placida dendritica. It seems to be photographed on Codium, or something similar, but the 'faded' look of the cerata suggest that it may not have fed for a while.

Have a look at Yasuhiro Shirai's message of a specimen from Japan, and Jui-Sheng Chan's from Taiwan.

Hopefully Cynthia Trowbridge or Kathe Jensen will give us an answer.
best wishes,
Bill Rudman

Dear Shauna,
You almost found some information on Placida dendritica. If you click on any word that is underlined it will take you to a page on that topic. Unfortunately I didn't underline Placida dendritica on the Solar Powered Sea Slugs page, but I have now.

So if you go to the Placida dendritica page you will find references to other pages with photos. There are also other messages on P. dendritica below yours on this page, which have more information which will be useful for you. You will see from reading those that there is some debate about whether Placida dendritica is one species found all around the world or a number of different species, each looking quite similar externally, but each restricted to a particular geographic region and probably having differences in anatomy and life history etc.

If you are looking for other information on the Forum try clicking on the buttons at the top of the page, using the SEARCH facility etc.

Good luck with your project,
You haven't been given the simplest 'species' to research.
Best wishes,
Bill Rudman

Dear Cynthia,
If you have photos of any of the other geographic 'forms' I would be happy to post them on the Forum for comparison. If any one can help Cynthia with specimens, it would be great to resolve just what "Placida dendritica" is.
Best wishes,
Bill Rudman.

Dear Cynthia,
Thanks for filling in the details. I remember when I was a student in Auckland, how we use to collect "Hermaea aoteana" & "Stiliger felinus" and watch them 'sneak up' on others of their kind and quickly stab them with their penial stylet. Clearly no thought of political correctness or sexual equality. I think it was not long after someone, (whose name escapes me), had published a paper on one of the species which aims so well at the hidden bursa copulatrix or sperm sac. What I find really amazing is the idea that in some species the injected sperm packet can somehow trigger off the growth of a sperm receptacle to enclose the injected sperm, and then grow a duct to connect the new sperm sac to the reproductive organs.

Best wishes,
Bill Rudman.

Dear Stephanie,
Thanks for the observations. I think this is what we are calling Placida dendritica. New Zealand animals of this species have been reported to mate by hypodermic insemination of sperm into their partner but usually near the position of the enclosed sperm sac. Random injection anywhere on the body has been reported in a couple of species of Elysia but not for stiligerids. It is possible that your animals are immature animals just 'practising' or that they are perhaps another species.

Best wishes,
Bill Rudman.

Dear Yasuhiro,
When I read that you found this on Colpomenia it made me wonder whether you had a species of Costasiella because I have found one living on Colpomenia. However in that genus the eyes are very close together and that doesn't seem to be the case in your species.

I think your animal is one that is usually called Hermaea dendritica or Placida dendritica. I am afraid there is considerable debate worldwide about whether there is one worldwide species or a number of similar regional species. See Cynthia Trowbridge's message suggesting there are many regional species at present being erroneously identified as Placida dendritica.

Best wishes,
Bill Rudman.