Dear Hugues,
I can't add much to my anatomical study of Phanerophthalmus in 1972. Certainly it seems to vary in colour from green or yellow to the greyish colour of one of your animals. Phanerophthalmus has a remarkable similarity in shape to an aglajid and for many years was considered a member of that family despite the fact that its internal anatomy was clearly that of a haminoeid.

Atsushi Ono's message [#1468] shows the colour variation as well and he includes an animal with a white W mark around the posterior edge of the head shield, which is the main distinguishing feature of P. albocollaris.  I suspect P. albocollaris is a colour form of P. smaragdinus but unfortunately, synonymising species [that is deciding they are not different] is much more difficult than making a new species, as you have to make detailed anatomical comparisons, look at variation in colour and shape etc, etc.  Of course these are the things that should have been done when the new species was proposed, but unfortunately it is often not done. As I have said on the species Fact Sheet, P. albocollaris was described from a single 3 mm long specimen, so we can't really say whether its distinct colour pattern is because it is distinct or because it is a juvenile variation of P. smaragdinus. A few other species of Phanerophthalmus have been described but there seems to be no easy way to distinguish them from P. smaragdinus on what we know of their colour and anatomy.

I can't really say if the colour of these animals is a result of the colour of their algal food. In sacoglossans the colour is often affected by the colour of the chloroplasts they acquire from their food, but in haminoeids the food is crushed and digested and chloroplasts are not retained, so they would need to have a mechanism to retain colour pigments from their food. The first step would be to find just what algae they eat. At present we don't know if they are specialist feeders or not.

• Rudman,W.B., 1972. The herbivorous opisthobranch genera Phanerophthalmus A.Adams and Smaragdinella A.Adams. Journal of Natural History, 5: 647-675.

Best wishes,
Bill Rudman

Dear Chuck,
The green animal is Phanerophthalmus smaragdinus, a primitive herbivorous slug with an internal shell. The grey-black animal in your lower photo is quite different. It is a marine snail, with a flattened shell partially hidden by folds of skin on its back. Have a look at the Scutus page for more information.

Best wishes,
Bill Rudman

Dear Philibert,
Congratulations to Alain for his photographic technique. I have tried to photograph Phanerophthalmus smaragdinus many times without great success. It is usually half covered in sand - or at least with some grit - in the field, and does not like crawling on smooth surfaces in the lab. I never thought to try photographing it on my hand! This species is a great example of just how often in the Cephalaspidea, shelled species have evolved into slugs independently. In fact Phanerophthalmus was considered for many years to be a member of the Aglajidae. However its internal anatomy clearly shows that its ancestry is amongst the haminoeids.
Best wishes,
Bill Rudman

Dear Atsushi,
I suspect that Phanerophthalmus gets some of its body colour from the algae it is feeding on, which could explain some of the colour variation from pink to dark green. I am not sure though about the black forms. The white edging at the posterior tip of the headshield in both pink and black animals does suggest they are the same species. I have seen small pink animals and larger ones ranging from a translucent pale green to a dark greenish-black but never pure black ones like the one in your photo.

The only way to be sure if they are the same species is to have a look their anatomy to see if we can find any differences in the shape of their teeth or gizzard plates.

Best wishes,
Bill Rudman.