Solitary or colonial coelenterates without any free-swimming medusa stage and with the coelenteron divided by mesenteries: The actinozoa include most of the common sea-anemones and corals.

Coelenterata consist of a rather large phylum of sedentary or free-swimming animals having a radially symmetrical sac-like body with a mouth at one end, usually surrounded by a ring of stinging tentacles.

The digestive cavity, known as the "coelenteron", has only this opening, but repeated budding may give rise to a colony in which all the body-cavities are connected with each other.

The body-wall is "diploblastic" that is made of two layers of cells, ectoderm and endoderm, with a gelatinous layer known as the "mesogloea" between them.

The individuals of a colony are known as "polyps" or "hydroids". They form the asexual sedentary generation which alternates with a free-swimming sexual phase known as the "medusa". The latter is a disc-shaped jelly-fish which breaks away from the parent colony and swims away. It produces gametes and after fertilization has taken place, a new polyp colony develops.

Included in the Coelenterata are corals and anemones in which the hydroid stage is dominant, jelly-fish in which the medusoid stage is dominant, and complex forms such as the "Portuguese Man-of-war" formed by a large floating colony of diverse polyps.

In zoology, the class of sedentary marine coelenterates: Anthozoa, or Zoophytes, are called "Actinozoa" including the sea-anemones, coralline polypes, etc.

They exist either in a solitary manner or in a colony and their tentacles surround a central mouth.

One organism of the class Anthozoa: An anthozoan is a marine invertebrate and can be a coral or a sea anemone, for example.