Flustra foliacea is a species of bryozoan found in the northern Atlantic Ocean. It is a colonial animal that is frequently mistaken for a seaweed. Colonies begin as encrusting mats, and only produce loose fronds after their first year of growth. They may reach 20 cm (8 in) long, and smell like lemons. Its microscopic structure was examined by Robert Hooke and illustrated in his 1665 work Micrographia.