Scientific Name: Stomatella varia 
Classification:     Mullusca
Common Names:

Description:
Stomatella look like a cross between a snail and slug. Their shell is fairly flat and inconspicuous compared to most snails.  They are brownish green in color and seem to stay under about 3/4" in length.  Stomatella can move very quickly for a snail.

Good or Bad?:
Stomatella are good additions to the reef tank.  They are herbivores and feed upon micro algae in the reef tank.

Notes: 
Stomatella are active day or night, but come out mostly at night and are fairly secretive during the day.  A look at the tank walls after dark with a flashlight will usually spot this critters if they are present in the tank.  They will reproduce in the reef tank, but don't seem to reach nuisance population levels.  Breeding has been observed during the daytime with all individuals climbing up to high points on the live rock and simultaneously releasing their eggs and sperm into the water.  This can cause the tank water to look milky for a short time, but is nothing to worry about.  The filter feeders get to eat well when this occurs.