For the half-serpents I'd say Naga. If I recall correctly they are half-serpent monsters from Chinese or Japanese legends.

For the half seahorses: Humacampus (derived from Hippocampus according to Wikipedia and huma from human.)

Aso, ArenaSnow, why would you use Dutch translate?

EDIT: Oops, Naga comes from India and Sri Lanka and such countries. My bad.