Thomas Mesaglio (CC BY)
Stomatella Snails
Stomatella spp. (family Trochidae)
Herbivorous algae grazers that never bother corals, fish, or other invertebrates.
Identification
Slug-shaped snails up to about 2.5 cm (1 in) long, with a small, flat, fingernail- or ear-shaped shell covering only the front half of the body and a long fleshy tail trailing behind. Colour varies widely — black, white, green, brown, orange, pink, or red, often mottled. Two antennae sit at the head. Mostly nocturnal and surprisingly fast for a snail; look for them cruising live rock and glass after lights-out.
Often confused with
Nudibranchs and pest slugs, because most of the body is soft and exposed. The separating tell is the hard, flat shell sitting on the back like a tiny saddle — nudibranchs carry no shell at all and show feathery gills or finger-like cerata instead. A Stomatella also has a clear snail head with antennae and grazes algae film as it moves.
Natural predators
No natural predators are listed.
Field notes
Excellent free cleanup crew: they graze diatoms and film algae, breed readily in reef tanks, and commonly arrive as live-rock hitchhikers. Keep them — many keepers would happily buy what showed up here for free.