Sea sponges are marine invertebrates of the phylum Porifera. Sponges consist of thin cell walls separated by a jelly-like substance known as mesohyl, which acts as the sponge's endoskeleton. Cells move through and around the mesohyl, and change functions regularly.

Sea sponges have pores and channels that allows water to flow through them in a system that acts as the sponge's digestive, respiratory, and circulatory system. Some sponges feed using symbiotic relationships with microorganisms, while others trap and feed on small crustaceans.

Sea sponges resemble coral, but are an entirely distinct species. In fact, sponges are a distinct evolutionary branch from all other animal species, who are known as "eumatazoans" in this context.

Dried sea sponges were used in ancient Greece as cleaning tools, owing to their ability to absorb fluids. While this practice still exists, most modern cleaning sponges are made of polyurethane or wood fibers.

By far the most notable fictional sea sponge is SpongeBob SquarePants, star of the American animated series of the same name, although his appearance reflects a household sponge rather than any living species of sponge.