Yes, MEDUSAE is a Scrabble word!

Letter values in Scrabble US: M 3, E 1, D 2, U 1, S 1, A 1, E 1.

Is it a valid word?

MEDUSAE is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

(Greek mythology) a woman transformed into a Gorgon by Athena; she was slain by Perseus
one of two forms that coelenterates take: it is the free-swimming sexual phase in the life cycle of a coelenterate; in this phase it has a gelatinous umbrella-shaped body and tentacles