Aquarium mystery

December 11, 1999
From: Kelly Greco

Dr. Rudman:

I have recently set up a reef aquarium. A couple of nights ago, I noticed a pair of what I believe to be some type of a sea slug grazing for algae (I assume) on the live rock. Tonight, I noticed a second of the same species. I am hoping you might help me to identify it. It obviously was introduced into the aquarium with the live rock which is from Fiji. The specimens in question show no type of an obvious gill, and do not swim freely but rather crawl over the rock at night. I have, therefore, only observed the dorsal side of the animal.

Description: Black (as night!!), oval shaped, approx. 2.5 cm in length, 2 cm in width. The main body is rather small ( < 1 cm) with the mantle (??) radiating outward as a skirt. There is a slit on the dorsal side which runs the length of the body and I believe is the anus as I have seen excrement being eliminated from it. At the anterior end, I can see two antennae extending from beneath the skirt or mantle. There seems to be a mouth similar to other herbivorous molluscs (such as Astrea sp.) That is also at the anterior end.

Again, I havent been able to observe the ventral side of the animal. Judging by it's locomotion, I would guess that it has a molluscan foot.

Any ideas??!! Any input is greatly appreciated.

Kelly Greco
Portland, Oregon USA

Greco, K., 1999 (Dec 11) Aquarium mystery. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Kelly,
If you could send me a photo or even a rough drawing it would raise my answer above that of a stab in the dark. One possibility is that it a species of Scutus, which is a slug-like snail, vaguely related to animal like the abalone, Haliotis. There is a photo of Scutus on the 'What is a Slug?' Page. If it is Scutus you will find an elongate white shell hidden beneath the two flaps which form the slit on its back.

Another possibility is a Sea Hare like Dolabrifera bit that is not quite the shape or colour that you describe.

If your animals are not like Scutus then I think I will need a picture - either photo or drawing to me of much help. If you can't scan an image to send then send it to me by mail at:
Australian Museum
6 College St,
NSW 2010

Best wishes,
Bill Rudman.

Rudman, W.B., 1999 (Dec 11). Comment on Aquarium mystery by Kelly Greco. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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