Clam

Clams are Pre-Hardmode enemies that spawn in the Sunken Sea biome. They are initially passive, but after being hit 3 times they become aggressive and chase the player, leaping around to attack them. They can drop Mollusk Husks in Hardmode with a 1/2 (50%) chance, which are used to craft Mollusk armor.

The Giant Clam can manually summon several Clams while hostile. It also boosts their spawn rate significantly via the Clamity debuff, which causes them to become instantly aggressive as well.