When a Fish Lives Inside a Sea Cucumber’s Backdoor 🐟 Meet the pearlfish — the slender, translucent freeloaders that hide inside sea cucumbers’ anuses for protection. Species such as Carapus and Encheliophis slip tail-first into the respiratory opening of a sea cucumber and spend their days inside the host’s cloaca, emerging at night to feed — or, in some species, feeding on the host itself. 🔍 What makes it extraordinary: Pearlfish enter through the sea cucumber’s cloacal opening, the same open

The sea cucumber plays an unusual role in its ecosystem. | National Geographic