Species of the family Beroidae are found in all the world's oceans and seas and are free-swimmers that form part of the plankton.

Like other comb jellies, the body wall of nudans consists of an outer epidermis and an inner gastrodermis, separated by a jelly-like mesoglea.

The mesoglea has pigments that give many nudan species a slightly pink color; Neis cordigera may be yellowish or a deep orange-red.

The mouth is zipped closed from each end, and the edges seal shut by forming temporary inter-cellular connections.

[3] Directly inside the mouth opening, in the lining of the gullet, can be found characteristic finger-like processes known as "macrocilia".

By this arrangement they effectively grip parts of the prey in synchronized waves like a conveyor belt, transporting it to the stomach, and the throat muscles promote this process.

The three-toothed tip of the macrocilia is stiff enough for it to rip the outer wall of larger prey such as other ctenophores; at the same time, proteolytic enzymes penetrate into the resulting wounds, rapidly incapacitating the victim.

They supply nutrients to the most active parts of the animal, the mouth, pharynx, combs of cilia and the sensory organs at the hind end of the body.

Each comb plate has its own meridional canal situated directly beneath it and a ring of channels surround the mouth.

In the late 1980s the ctenophore species Mnemiopsis leidyi was introduced into the Black Sea, probably through ballast water, which led to the collapse of the local anchovy population.

This division, after provisional results of morphological and molecular studies, however, probably does not reflect the actual relationships within the ctenophores.

The monophyly of Nuda is widely accepted, due to the complete lack of tentacles, and the presence of macrocilia as a common secondary feature, or synapomorphy.