Jellyfish have a single opening that serves as both their mouth and anus.

Jellyfish

Sponges have specialized cells that allow them to expel waste without a dedicated anus.

Sponges

Some members of the cnidarian group, like corals and sea anemones, lack a separate anus.

Cnidarians

Flatworms

Certain flatworms use a simple system of branched tubes to distribute nutrients and expel waste.

Tapeworms

Tapeworms absorb nutrients directly through their skin, eliminating the need for a separate anus.

Roundworms

Nematodes have a complete digestive tract but often lack a distinct anus.

Comb Jellies

Some ctenophores have a single opening for both eating and waste expulsion.

Rotifers

These microscopic animals use a specialized structure called the "mastax" to process food and eliminate waste.