What is this??

[CaptDan]

Looks like a snail without a shell it’s purple

 

[Peace River]

Others will likely chime in soon, but it looks like some type of sea slug. Can you share pictures under white lights?

 

[NicholasP]

I think I have the same in my tank, they came with the live rock. They're more whitish when young, but have two antennae and a proboscis. They are covered by half a shell on their back, I think they are called stomatellas and they're harmless. They haven't bothered any of my corals and just go about their day eating algae

 

[Peace River]

I think I have the same in my tank, they came with the live rock. They're more whitish when young, but have two antennae and a proboscis. They are covered by half a shell on their back, I think they are called stomatellas and they're harmless. They haven't bothered any of my corals and just go about their day eating algae

Good call out! That is likely the type of sea slug that it is, but I was asking for a better picture to confirm. Like you said, they are reef safe.

 

[EeyoreIsMySpiritAnimal]

Stomatella

 

[NicholasP]

Also, when I had a bloom of hairy algae in my tank, their population increased tremendously, I had 2 or 3 tiny white ones, and they were constantly grazing, and some nights I saw them shooting a white liquid. Now I have like 5 or 7 pretty big ones, but i don't bother removing them, I keep them as a part of my cuc along w my snail, hermit and urchin. There's always enough food for them as I never scrape the rear glass panel of my aquarium, because they've cleaned everything and I leave that there as a food source that they all go crazy on every day.