Long Spine Urchin in Small Tank???

[Myka]

As many of you know I have some baby Bangaii Cardinals. I was looking through our local classifieds and happened upon an ad for a "small black long spine urchin". Now, I have seen some tiny 1" long spine urchins, and I've seen some well over 12". I left a message to find out what the actual size of it is. I have my little baby Bangers in a 10 gallon right now. It is an established tank having been setup for over a year, however it is BB, just has an AquaClear 100 for filtration, only PVC for hiding, and a single astraea snail to keep it low on the algae. The Bangers are in one of those "net breeder" thingies to protect them from the AquaClear until they get bigger.

The long spine urchin is a natural hideout for the baby Bangers...what would I have to do to keep this urchin in the tank with them? How quickly will it grow? What does it eat?