Identity of Nudibranch mimic

March 23, 2002
From: Raymond Mears

Dear Dr.Rudman:
I purchased two organisms March 9,2002. They were identified to me as Nudibranchs and algae eaters. I have filimentous algae getting out of hand and figured the people had watched long enough to know proper feeding. I knew at the time they were not Nudibranchs but if they cleared the algae and did not eat coral who cared? My first thought was strange chiton but no plated back and in fact the backs are without shells.

It is now March 21. They do not eat the coral. They do not eat. One no longer grasps the aquarium wall with a firm foot. I suspect they are dying. Before I took your time I regarded it as my duty to do my own research. That did not take long. Suspecting from your page what I might have, I entered Lamellariidae and Velutinidae into search engines. Results were several taxonomic lists. I looked over the feeding info. on your site. I tried the strings feeding Velutinidae and feeding Lamellariidae on your site getting no results.

I have no scanner or close up camera so will give a verbal description. I have seen how often you must tell people they have no hope for feeding some creature and expect the same reply. I would, at least, like to know what I am starving to death. We both reside in English speaking regions so measure is non- metric and only approximate. Largest snail is 1"3/4 long by 3/4 wide. Chiton like hump back max height perhaps 3/4". Unlike a chiton the body can bend to L shape in movement. Back shows no siphon opening, like some of your pictures, on the forehead. Upper body colour is black. Irregular grey patches run longitudinally on top 1/3 of body but are circles or run perpendicular to body axis on sides. Orange knobs are scattered on the grey. They are slightly irregular in size and spacing. At times they will flatten some of the nodules and drop the orange to gray. When they move about, the"forehead" has nudibranch like orange antennae.When they sit still these are not obvious. They do not move much these days.You may know what they mimic which would tell us a little about them.

Moving to the underside,they do have real antennae of about 1/8". Sometime obvious sometime not. I do not see eye spots at the tips. The stalks, foot, entire under surface is gray. Foot has a dark center line. Foot border is crenulated. I have never seen a radula.Do not even see a well defined mouth. I think I have seen an anus at times. Somewhere in reference to the velutinidae I think you mentioned an abalone like foot. That mantle to the substrate,space all around perimeter then foot look is present here also. They leave a slime trail like a garden snail when they move. In fact,when
first obtained they exuded slime from the upper surface as well.

I hope this is enough info. to give me some likely suspects.
Raymond Mears

Mears, R., 2002 (Mar 23) Identity of Nudibranch mimic. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Raymond,
I suspect your animals are a nudibranch of the family Phyllidiidae. Have a look at the page on Phyllidia varicosa. If I am right the slime they exuded from the upper surface when you first got them would have been a white stringy sort of substance. If so, you were lucky they exuded this before they had much contact with your aquarium because the chemicals they exude can be quite toxic to aquarium fish and when freshly caught if the aquarium they are in is left in a closed room there air can become so acrid that your eyes can start streaming and stinging.

Phyllidiids like all nudibranchs are carnivores, in the case of phyllidiids, each species feeds on specific sponges. The chances of matching your slug with its correct food sponge are slight to non-existent. I suppose you should confirm that your slugs are phyllidiids before I suggest what you should say to the person who sold you these as algal eaters. One final check would be to check on the underside of the body to see if it has gills in the gap between the foot and the mantle. [If you look at the page on Torsion and gills there is a photo on the bottom left of Phyllidia ocellata showing typical Phyllidia gills].
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Mar 23). Comment on Identity of Nudibranch mimic by Raymond Mears . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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