MNN Galleries

8 uncanny animal lookalikes

Flatworm (L) and sea slug (R)

Photo: Wikimedia Commons

7 of 10

Flatworms and sea slugs

Flatworms (left) often mimic sea slugs (right), but the species are quite different. Flatworms lack body cavities, respiratory organs and circulatory systems — they're pretty much just flat animals with holes for food to go in and out. "Sea slugs" is a term that describes many differents kind of marine creatures including shell-less saltwater snails and nudibranchs. Nudibranchs are conspicuously colorful mollusks that can secrete toxins as a defense mechanism, so it's easy to see why flatworms might evolve to look like them.