Dear Andrej,
There is no need to feel humble - all views are welcome. From the work of Ortea et al (1996) I would agree that Marina's animals in message #16619 seem to be H. malacitana. However the animals in her message #9683  look identical to the animals, also from Senegal, in Fig 6 F, G of Ortea et al, where they are are identified as H. bilineata.. There seem to be two differences. In the Senegalese version of H. bilineata, the central part of the mantle has whitish spots or lines arranged longitudinally and bordered by a yellow line. In Senegalese H. malacitana, the central part of the mantle has scattered yellow spots, sometimes with a median line of spots as well.

Marina appears to have provided us with an interesting selection of photos of 'blue chromdorids' from Senegal. I guess only further study will clarify whether we are dealing with a single variable species, or two different species which appear to be mimicking each other.

Again I must say I have no personal experience with these species so I am guided solely by the published literature and photos on the Forum. I would appreciate further input

• Ortea, J., Valdés, A. & García-Gómez, J.C. (1996) Revisión de las especies atlánticas de la familia Chromodorididae (Mollusca: Nudibranchia) de grupo cromático azul. [Review of the Atlantic species of the family Chromodorididae (Mollusca: Nudibranchia) of the blue chromatic group.] Avicennia, 1996, Suppl. 1: 1-165.

Best wishes,
Bill Rudman

Dear Marina,
I totally agree with your doubts about H. cantabrica and H. malacitana which I have discussed in an earlier message [#14740]. Clearly there is more work to be done with this group. I don't suppose you would have any photos of the egg ribbons of Seneglaese animals. It would be nice to compare them with your photos of H. cantabrica [#12746 ].

Best wishes,
Bill Rudman

Dear Valerie & Marina,
I agree these are very interesting animals. I think they also illustrate that we still have a lot to learn about the Atlantic 'blue chromodorids'. They certainly have similarities in colour to H. bilineata, but the distinctive feature in that species seems to be the median double yellow line on the dorsum. Edmunds (1982) identifies animals from Ghana, with white lines inside the yellow lines as H. bilineata, and Ortea et al (1996) do the same with animals from Senegal. In the animals in your message there are no median yellow lines, although there is a single median row of yellow dots in one animal. Instead the prominent feature are the fine yellow dots scattered all over the central part of the mantle and the sides of the body. 

I don't know if you have a copy of Ortea et al (1996), but although I am puzzled by some of the decisions in that revision, it is the best summary available. In that they have a photo (Fig 7E) of a juvenile of H. malacitana which has the same basic colour pattern as your animals, although the spots are a little larger.

I am posting a number of messages today on 'blue chromodorids'. I hope some local experts can give us their opinions.

• Edmunds, M. (1981) Opisthobranchiate Mollusca from Ghana: Chromodorididae. Zoological Journal of the Linnean Society, 72(2): 175-201.
• Ortea, J., Valdés, A. & García-Gómez, J.C. (1996) Revisión de las especies atlánticas de la familia Chromodorididae (Mollusca: Nudibranchia) de grupo cromático azul. [Review of the Atlantic species of the family Chromodorididae (Mollusca: Nudibranchia) of the blue chromatic group.] Avicennia, 1996, Suppl. 1: 1-165.

Best wishes,
Bill Rudman

Dear David,
I think this is Hypselodoris malacitana, but I am having some difficulty deciding the difference between this species and H. cantabrica. Both species seem quite variable in colour and both have colour forms with a median yellow line on the dorsum. Ortea, Valdés, García-Gómez (1996) mention that one of the distinguishing features of H. malacitana is a yellowish line down the posterior midline of the rhinophore which splits basally to form an inverted V. Looking at the photos of H. cantabrica on the Forum [messages #2124, #12745] they also have this same marking. If they are both H. malacitana as well, I have no idea how the two species can be differentiated. Any advice would be welcome.

• Ortea, J., Valdés, Á. & García-Gómez, J.C. (1996) Revisión de las especies atlánticas de la familia Chromodorididae (Mollusca: Nudibranchia) de grupo cromático azul. [Review of the Atlantic species of the family Chromodorididae (Mollusca: Nudibranchia) of the blue chromatic group.] Avicennia. Revista de Ecologia y Oceanologia y Biodiversidad Tropical. Supplement 1. 165pp.

Best wishes,
Bill Rudman

Dear Isabel,
These 'blue chromodorids' are indeed easy to misidentify, so like you I hesitate to sound to confident. However I am pretty sure this is Hypselodoris malacitana. The yellow mantle border with a thin dark blue line on the inner and outer edge seems quite characteristic, as does the lighter blue submarginal band. If it is H. malacitana it is an interesting find, for as far as can can determine this species has previously only been recorded from the Spanish coast of the western Mediterranean.
Best wishes,
Bill Rudman

Thanks Luis,
I can't find any reference to its food in Ortea, Valdes & Garcia-Gomez (1996). In the upper photo it is on a sponge you identify as a species of Ircinia. Do you know if that is its preferred food sponge?
Best wishes,
Bill Rudman