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Thumbnail of schematic Anthozoan diagram
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Like other polyps of the phylum Cnidaria, anthozoan polyps consist of a tubular body terminating in a mouth surrounded by a ring of tentacles. These are usually arranged around the periphery of the mouth disc and are hollow, with coelenteric space expanding into them. The polyp wall consists of an external layer (the ectoderm) and an internal layer (the endoderm). In between lies the mesoglea, which is cellular and thicker in anthozoans than in other cnidarian polyps. Some forms secrete an external or internal skeleton (corallum) that can be calcitic, aragonitic, horny or chitinous.

The two characteristic morphological features of anthozoans that distinguish them from other cnidarian polyps are:

In most species, the actinopharynx contains at least one siphonoglyph, a specialised flagellated longitudinal channel for driving water into the coelenteron.

Each radial chamber is in contact with one hollow tentacle. The mesenteries provide increased surface area and structural support, they also contain muscles and other important organs, such as tuberous mesenteric filaments for the fermentation and resorption of food. The mesenteries also contain reproductive cells in the endoderm.

Anthozoa have a nervous system that forms a network, enabling coordinated movement of body parts. Most orders contain colonial species exclusively; these colonies consist of polyps connected by living tissue (the coenenchyme).

The septa (or mesenteries) impart a radial symmetry on all anthozoans. Siphonoglyphs and bands of muscle along mesenteries impart a bilateral symmetry.

Author: Ben Kotrc
Last updated: 21 November 2005
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