Hippocampi

Hippo campus Hippocampi 

(singular Hippocampus) these creatures are internal servents of Poseidon and his children.

Habitat
Open oceans, reefs and underwater kingdoms

Diet
Kelp and seaweed

Behavior
They are social creatures often living in pods. They are also very loyal to they're rider's and friends.

Biology
They are mammals having both horse and dolphin features.

Appearance
Length: 8-12 feet They have a horse-like front and head and a dolphin tail. It's skin is whale-like but with shining scales on the backs.

Tips for demigods
They are alot like Pegisi, always loyal and useful