Those are the little tiny shellie ones. I
I've always wanted some but have found them difficult to find. I believe Mike Dunagan has some. You could ask him about their care.
Shellies can go in a 30 fine. They are not as large, but I think a little more agressive than the other types. The shellies are harder to find. Mine jumped the tank after a move. So I am the lookout for some new ones. I have most types of comps and calvus. I keep them in a 125.