Centaurs
Typically Centaurs have the upper body of a man and the lower body of a horse. A breed of ocean dwelling Centaur has the upper body of a man, the midsection of a horse, and the tail of a fish.
Maenads
Immortal female followers of Bacchus.
Nereids
A type of sea nymph, daughters of Nereus. They care for ocean life and sailors in distress. They are depicted as beautiful women with webbed feet or small tails.
Satyrs
Depicted with the body of a man, the tail of a horse, ears of a donkey, and sometimes the lower body of a goat. They are stout with round and flat noses. They reside in the countryside.
Sea Hybrids
Combinations of various different animals (such as bulls, goats, horses etc.) with fish tails.
Sons of Silenus
Similar to elderly satyrs. Fathered by Silenus.
Tritones
Half man have fish tailed monsters. Followers of Neptune, the sea god.
Also mentioned...
Minotaur
The half bull half man hybrid trapped in the labyrinth on Crete. Half brother of Ariadne. Killed by Theseus.