I think I have seen this species before on another site. I can't remember which one it was but I think the diet consists of gorgonians. That is if this is indeed the same species.
from the looks of it I doubt it eats algae. Probably carnivorous in one way or another since it has that sensory snorkel nassarius snails have. Might even be venomous.
My first impression is that it is some kind of small carnivorous snail. It resembles the Atlantic Flamingo Tongue snail which eats only gorgs but it is a very different type of snail.