Thorncracker Gilltail

The thorncracker gilltail split from its ancestor and has specialized in eating the thornstack. It uses it's strong beak to crack and break the thornstack's hard, thorny shell. It then eats the resulting pieces. It is black and dark blue so it can blend in with blocks temperate river's black mud and the thornstacks' dark blue bodies. Paradoxically, the camouflage is useless because it has no predators. It's population is kept in check by the limited amount of thornstacks to feed.