Another Scutus in live rock

March 5, 2002
From: Becky

I am a novice reef keeper on a small scale (20 gal.) and I have been trying to identify a slug type creature that came in on some live rock I purchased for my tank 6 months ago. It appeared to be a hole - until it moved. Most of the time it is disc shaped although it can elongate. It can ruffle its edges and looks like a snail from the underneath (when it's on the glass). It usually has a hump in the center and has 1 white stripe down the back, although it can vary the thickness of this stripe to the point of disappearance when it wants to. It seems to be able to contort its body to any shape or dimension necessary to conceal itself in live rock. For a long time it would not come out into the light, but it seems to be less shy now. I think it eats slime algae as I see it frequently attatched to the glass. I have 2 azure damsels (1.5" ea.), 1 percula clown (1.75"), 1 green mandarin, small red hermits, small algae snails (astrae), & 2 emerald crabs. None of the other residents seem to bother this black creature, although for a long time he seemed to be fearful. My primary interest is how safe this creature is. Eventually, I plan on adding some leather corals & mushrooms. Do you think this black thing will bother them? I don't have a picture & have looked in vain on the slug pages for something resembling this creature.

Becky, 2002 (Mar 5) Another Scutus in live rock. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Becky,
You don't say where your live rock came from but I suspect your animal is animal is Scutus, a 'snail' rather than a 'slug'. The white stripe you can see on its back is part of its flat white shell, which appears to vary in size because it is partially covered by a flap on each side of the body, which can expose or cover the shell as it extends or contracts. Have a look at the photos on the Fact Sheet. Scutus seems to be a common 'hitch-hiker' on live rock and seems to thrive in home aquaria feeding, as you suspect, on algal film. Far from being a problem in your aquarium, it could be a useful addition to your tank.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Mar 5). Comment on Another Scutus in live rock by Becky. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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