sea monster
mythical or legendary creature, believed to dwell in the sea and often imagined to be of immense size
Loch Ness Monster
lake monster of Scottish folklore
Charybdis
figure in Greek mythology transformed in a sea monster by Zeus
Scylla
nymph transformed into a sea monster by Circe in Greek mythology
kraken
legendary sea monster of large proportions
Cetus
sea monster or large sea creature
Sea monk
marine monster of the Renaissance
water horse
mythical creature
Tannin
Biblical demon or monster