What is this?

[Nano]

Originally Posted by Mandosh

Same class as nudibranchs...both gastropods.

Stomatella varia. It's a herbivore and it's harmless. Great little algae eater.

+1 I have a few in my tank I thought they were nudibranches at first, but these guys are beneficial where as nudis are detrimental in most reefs depending on the variety! keep him like said above he's a good little algae eater!