These creatures are foul things that prey on the weakness of loss. Their home society, and indeed, their home, in completely unknown, as all that have been found have been killed to out standards.
Rich Romans raised fish in private pools at their villas. A favorite fish was lamprey, a parasitic fish which sucks off blood and flesh but made an excellent meal. A particuarly gruesome punishment for slaves was to be thrown into the lamprey pool, where their flesh was ripped from the bone by swarms of the jawless fish.