Ninja Star snails is our descriptive name for this species of star snails.  They were formally named Astrea phobia, but the new scientific name for them is Lithopoma phobium.  They are closely related to the regular “astrea “ star snails, but have very pronounced spikes around the edge of their shell throughout most of their life.  They get quite a bit bigger than the standard astrea snails, and when full grown they can be 2” across.

 

These snails inhabit pretty much the same habitats as the other astrea snails, but they are very difficult to find and available in very limited quantities.  They will eat just about any thin film algae, but will also eat hair algae and other nuisance algae.  They don't seem to eat coralline algae, and usually don't bother caulerpas, most calcareous algae, and most fleshy macro algae.  They may forage on some of the larger algae, but unless they are really hungry they don't tend to eat them.  They don't generally eat bubble algae; so if you're having a problem with it, get some green or red mithrax crabs.