What is a small shellfish that clings onto ships?

Barnacles are crustaceans that live attached to surfaces, often in marine environments. They have a hard, shell-like covering and use their appendages to filter food from the water.

There are many different types of barnacles, and some of them are known to attach to ships, piers, and other structures in the water. This can be a problem because barnacles can increase the weight and drag of a ship, making it less efficient.