One atypical South American species, Hygrocybe aphylla, lacks gills.

Both groups lack true gills on the underside of their caps, though they often have gill-like wrinkles and ridges.

It is very similar in appearance to Hypselodoris maridadilus but that species lacks the white-tipped rhinophores and gills.

Like all acochlidians, it lacks plicate gills.

At the close of the Devonian, forms with progressively stronger legs and vertebrae evolved, and the later groups lacked functional gills as adults.

The mantle cavity is located on the right side of the body, and lacks gills, instead being converted into a vascularised lung.

Since they lack gills, they go to trapped pockets of air in the submerged nests to breathe.

The gill is flaplike with a bipectinate ctenidium situated in the nuchal cavity and lacks secondary pallial gills.

Some terrestrial species lack both lungs and gills and perform gas exchange through their skin.

Nemerteans lack specialized gills, and respiration occurs over the surface of the body, which is long and sometimes flattened.