Odontogriphus

Odontogriphus is part flatworm, part leech, and swims with a manta ray's rippling glide. Beneath its body is a mouth ringed with odd teeth.

It settles onto prey from above, latches on with that toothed ring and feeds. The bite deals 1d6, then blood drain adds 1d4 every round. Pulling free takes a successful Strength check, or under the companion science-fiction rules, a Fitness check at -10.

Its flexible body can also smother a man-sized or smaller victim, wrapping around it the way a lurker above does. Each constriction attack adds 1d6 damage, and the victim suffocates within 1d4+1 rounds at most. A personal air supply underwater does not help, because the squeeze keeps the lungs from filling. Anyone striking the creature while it is wrapped around someone also deals half that damage, rounded down, to the trapped victim.