unknown hitchhiker

looks like a pod. get a fish that will eat it.

isopod maybe?

Those jaws make it look awful like a parasite. Doesn't look like the kind of feeding apparatus I'd expect on a detrivore.

Big teeth and horns to boot! Looks dangerous.

Fish Lice.

Isopod. those arent jaws; thats its hind end. if its got big black eyes, then its the bad kind. if its got little eyes (barely visible) on the sides of the front end, its probably not the parasite kind.

it looks like that thing from aliens