Nereid n. : A sea nymph, one of the daughters of Nereus, who were attendants upon Neptune, and were represented as riding on sea horses, sometimes with the human form entire, and sometimes with the tail of a fish.

Nereid n. : Any species of Nereis. The word is sometimes used for similar annelids of other families.

Example:
How far away is Nereid from neptune?

Taxonomy
Nereids, Callianassa, Cymothoe, Doto, free encyclopedia, Halimede, Cymo, Neso, sea nymphs, crab, Thetis, depths, cave, wife, salt sea, Iaera, Proto, Dexamene.

Defination from the web:
Nereids (neer'-ee-eds) (Νηρηΐδες) are sea nymphs, the fifty daughters of Nereus and Doris. ... There gathered round her every goddess, every Nereid that was in the deep salt sea. ...