Crustacean?

Crustacean?

Observation - Crustacean?. Description: Found in a pool of seawater on the Isle of Skye, this animal is about 5 cm long (as far as I can remember). Could anyone please tell me, what kind of animal this is and if it is commonly found there?

Found in a pool of seawater on the Isle of Skye, this animal is about 5 cm long (as far as I can remember).
Could anyone please tell me, what kind of animal this is and if it is commonly found there?