Orange-Tentacled Flame Shell

Flame shells live in enormous colonies, but hidden in nests.
Graham Saunders, Flickr

A colony of 100 million flame shells (Limaria hians) was discovered in Scotland in 2012, and is thought to be the biggest in the world. Flame shells are bivalve mollusks that are shaped a bit like scallops—but they have bright orange tentacles exuding from their shells. Despite their bright color, flame shells are very hard to spot because they hide in self-constructed felt-like nests. They bind together stones and shell pieces to build a nest, and hide within. The only way to see the live animal is to tear open the nest.