Choose the word which is different from the rest.

Answer: Option E

Options A, B, C, and D (Oyster, Clam, Scallop, and Mussel) are all types of shellfish, specifically bivalve mollusks.
A bivalve mollusk is a creature that lives in the water and has a shell made of two parts hinged together.
Option E (Mast) is a tall pole or structure, usually on a ship or boat, used to support sails or antennas.
Therefore, it's the only option that is not a type of shellfish.