Yes, THORAXES is a Scrabble word!

Letter values in Scrabble US: T 1, H 4, O 1, R 1, A 1, X 8, E 1, S 1.

Is it a valid word?

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

the middle region of the body of an arthropod between the head and the abdomen
the part of the human torso between the neck and the diaphragm or the corresponding part in other vertebrates
part of an insect's body that bears the wings and legs

Not playable in Scrabble US: PECTUS.