Ok, my first question would be is an urchin an invertebrate? Hope so. Anyway, we have put nothing new in our tank for maybe 4 months. Suddenly we have an urchin. It is kinda big to be missed for so long, about the size of a 50 cent piece I would say. We have no idea how it got in there, must have hitch hiked on something and then been like a 007 urchin and hid out. Is this something we can leave in there? Will it multiply and take over the tank? It hasn't moved for about 2 weeks. Weird huh?
Wendy