Yes, SWIMMERET is a Scrabble word!

Letter values in Scrabble US: S 1, W 4, I 1, M 3, M 3, E 1, R 1, E 1, T 1.

Is it a valid word?

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

one of the paired abdominal appendages of certain aquatic crustaceans that function primarily for carrying the eggs in females and are usually adapted for swimming