Dear Kevin,
Yes the flattened triangular shaped flaps are its oral tentacles. Most chromodorids have more tapering cylindrical tentacles, so this is an interesting observation. I don't think its a character of the genus Mexichromis however, because species I am familiar with from the Indo-West Pacific don't have this shaped oral tentacles. I guess its another thing to add to the 'to check up' list.

Best wishes,
Bill Rudman

Dear Aidan,
Thanks very much for thinking of us. These animals have their reproductive organs on the right side of the body just behind the rhinophores, so from the way your two animals are aligned I suspect they are not actually mating. But I suspect their position is either pre- or postnuptial.

Another interesting thing in your photo is the bluish grey patch below the two nudibranchs. McDonald & Nybakken (1978) reported that this species feeds on the sponge Dysidea amblia, and this patch could well be a dysideid. I am sure one of out west coast colleagues can correct me if I am wrong. Some dysideids are often partially covered by sand grains or have them incorporated in their outer layers, which can make it very difficult to know if a chromodorid is feeding on a sponge or just crawling over a patch of sand. My guess is that these two animals are together because of the food sponge. That is not to say they won't mate - but to be totally unromantic, the initial attraction is the food, rather than the beauty of the nudibranchs.

• McDonald, G.R. &  Nybakken, J.W. 1978. Additional notes on the food of some California nudibranchs with a summary of known food habits of California species. The Veliger, 21(1): 110-118.

Best wishes,
Bill Rudman

Thanks Clinton,
It's good when a topic stimulates some more messages. Your animal seems to be on a mixed assemblage of sponges, cnidarians and ascidians. Mexichromis porterae has been reported to feed on a species of Dysidea, but as luck would have it I can't see anything looking like Dysidea in your photos. Some chromodorids seem to always be found with their food while others are seldom seen near anything identifiable.
Best wishes,
Bill Rudman

Dear Chris,
Thanks for another photo of this species. It is nice for you to be able to compare it with the very similarly coloured Chromodoris macfarlandi at the same time [see message #14430 ]. If you ever catch it on its food sponge or laying eggs, photos would be very welcome
Best wishes,
Bill Rudman

Dear Amber,
What a spectacular way to make a debut on the Forum! It is indeed a beautiful animal. Sorry I didn't have a size indication on the Fact Sheet - which I have now added. Dave Behrens (1991) notes that it grows to 35 mm in length
Best wishes,
Bill Rudman

Thanks Chris,
It's nice to get photos of this species which is so similar in colour to Chromodoris macfarlandi and Hypselodoris californiensis. We have a group of red-spotted chromodorids in southeastern Australia. All chromodorids have noxious glands in their skin and we think these groups of similarly coloured species have evolved because it is easier for fish predators to learn to avoid just one colour pattern.
Best wishes,
Bill Rudman

Dear Lacey,
Great news on your project. Thanks for letting me know how it went.
Best wishes,
Bill Rudman.

Dear Beth,
Have a look at the answer I gave to Lacey Keen, a classmate of yours, a few days ago, to the same question.
best wishes,
Bill Rudman.

Dear Lacey,
You're lucky that Mexichromis porterae is one of the few Californian nudibranchs I have a picture of on the Forum. Like many nudibranchs, I don't think a lot has been published on its biology and natural history. One important point for you to know though is that for the last 20 years it has been placed in the genus Mexichromis, rather then Chromodoris, because parts of its anatomy (eg: radular teeth, reproductive system)are rather different from those found in species of Chromodoris.

Like all chromodorids, Mexichromis porterae is a sponge feeder, and has been reported by a number of authors to feed on the sponge Dysidea amblia DeLaubenfels. Chromodorids, like Mexichromis, have some very interesting defence mechanisms. Like many plants, sponges make and store in their tissues, a variety of distasteful chemicals to deter animals from eating them. Sponge-feeding chromodorids are not affected by these chemicals and remove them from the sponges they eat, and store them in glands around the edge of their mantle. In combination with their bright colour patterns, predators, such as fish, apparently learn that these nudibranchs taste terrible and aren't worth eating. Have a look at the pages on Defensive Glands, and Mexichromis macropus. Also have a look at the section on 'Warning Display' in the Defence - Colour Patterns Page. Mexichromis porterae is one of a number of species on the west coast of America with a blue and yellow colour pattern, suggesting a mimicry group like the red-spotted chromodorids of south-eastern Australia. Have a look at Mike Miller's messages illustrating some of these West Coast animals - though I think they are all yellow spotted rather than yellow-lined. I guess you are familar with Dave Behren's book Pacific Coast Nudibranchs which will also give you some background information. All I can find in the literature on other aspects of their natural history is that they are fairly uncommon and found from the intertidal to about 18m depth. Perhaps someone with further information will let us know. For example does anyone know if they have free-swimming veliger larvae or direct development?

About the last part of your essay topic What is it's place in the biosphere?. It's not possible to answer such a question. To me it suggests there is some plan to nature and the environment, which is wrong. Evolution is directionless and without a plan. That's how it works. Nudibranchs don't have a 'place' or a 'purpose' they just 'are'.

Closely related species have their own food requirements and possibly other slight differences in ecology. However, because at any one place, the actual species present, and their numbers, can change over time, the inter-relationships between species is continually changing. You can say that Mexichromis porterae has a direct predator-prey relationship with the sponge Dysidea amblia but every other relationship it has with the fauna and flora at that place is in a continual state of flux. Sorry there is no easy answer to life's big questions.

Good luck with your assignment,
Bill Rudman.

Thanks Scott,
It's quite a coincidence that your photos have arrived at the same time as I am posting Roberto Moresco's photos of Hypselodoris messinensis from the Mediterranean, where, as I am sure you know, there is another, somewhat bigger collection of blue chromodorids with yellow markings. It's good to hear from you.
Best wishes,
Bill Rudman.