What kind of urchin is this?

[sakeating]

I think it might be a hairy pin cushion urchin, but I'm not sure. Secondly, how many of these can live in a 40g tank? Because i have 3. They all hitchhiked in on live rock. The largest one is about the size of a gold ball. The other 2 are quite small, maybe about the size of a penny. The largest one started out in my 20 really tiny and over about 2 months grew to this size, so he's grown quite a bit. How much larger can I expect them to get?

Thanks!

[TheGreatAukSociety]

An E. viridis short spine urchin. They grow fast the first year. But slow down and stay small. 40 gal can keep 1 adult.

I keep the in reef tanks. They eat hair algae. And are even covered in this weekends meeting.

[sakeating]

Awesome. Thanks for the info. Unfortunately I can't make the meeting :( Saturdays don't work for me. How does one catch one of these? Other than removing the rock it is on?