Pleurobranchus albiguttatus from Reunion Island

Dear Hugues,

While preparing your message I was surprised to see the treatment of P. atlanticus in the new book by Valdes et al. (2006), Caribbean Sea Slugs. I have discussed this in more detail in a separate mesage [#18917 ]

In my opinion the most distinctive external feature of P. atlanticus  is the series of larger tubercles down each side of the midline which each have a white triangular mark on them.  This is also the most distinctive external feature on the Indo-West Pacific species P. albiguttatus, and as I say in my earlier comments [#5301] I wouldn't be surprised if P. atlanticus turns out to be the same as P. albiguttatus.

It is interesting that your juvenile has a thin orange mantle border. Anne Dupont [message #5301] sent us a photo of two white juveniles, from the Caribbean, with a thin orange border, which I identified as P. atlanticus, which again reinforces the similarity between these two species.  Mind you it is not unique to those two species as I illustrate a similar coloured juvenile of P. peroni on the Fact Sheet for that species.

So to your question about whether P. atlanticus is a synonym of P. alboguttatus, I can say we need to recheck their anatomy, but if I were a gambling man. I think I would put a lot of money on a 'yes' answer.

One interesting feature we can see in your photo [middle right] of the underside of the animal is the intense white elongate patch at the posterior end of the sole of the foot. This is a gland which develops in most species of Pleurobranchus as they reach maturity. I am pretty sure no one has ever studied the function of this gland - another one of the many things we still have to learn about these animals

Best wishes,
Bill Rudman