Yes, METAZOA is a Scrabble word!

Letter values in Scrabble US: M 3, E 1, T 1, A 1, Z 10, O 1, A 1.

Is it a valid word?

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

multicellular animals having cells differentiated into tissues and organs and usually a digestive cavity and nervous system
any animal of the subkingdom Metazoa; all animals except protozoans and sponges

Also: subkingdom metazoa.