The anatomy of corallimorpharian polyps is quite similar to that of stony coral polyps. However, there is a great deal of variation between the various families and genera, and there is no "basic" internal anatomy.
Polyps consist of three layers. The internal endoderm surrounds the interior gastrovascular cavity. This cavity contains numerous outgrowths of the endoderm called mesenteries, the gonads and mesenterial filaments. Gonads develop along the mesenteries. The mesenterial filaments are a simple cord of cnido-glandular material. All genera have an abundance of nematocysts embedded within the endoderm. A single mouth (actinopharynx) connects the gastrovascular cavity with the external environment. Some species have an indistinct siphonoglyph but most do not have one. The outer layer, the ectoderm, tends to be thin and lacks nematocysts in some genera. Between these two layers lies a layer of tissue called the mesogloea, which can be rather thin in soft and flexible genera (e.g. Discosoma) and thick in more rigid genera (e.g. Amplexidiscus, Co ra Hi m o rph us).
The polyp itself consists of a base that is firmly attached to the substrate in some genera (e.g. Corynactis, Ricordea and Discosoma) wiiile deep sea genera are often free-living (e.g. Nectactis) (den Hartog, 1980). The body column tends to be smooth and lacks specialized organs and can occasionally be separated into a scapus and scapulus. The oral disc can be smooth with small, bump-like tentacles (e.g. Discosoma) or can be covered with captitate tentacles (e.g. Rhodactis). Tentacles can be very reduced or elongated, sometimes with swrollen tips (acrospheres) along the oral disc margins, depending on the genus and/or metabolic state of the animal. The tentacles of some species are retractile while in others they are not (see chapter nine). For more detailed descriptions of polyp anatomy of the various genera, please refer to chapter nine.
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