INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

DIVISION DIPLOBLASTICA, OR RADIATA

PHYLUM CNIDARIA, OR COELENTERATA

SUBPHYLUM ANTHOZOA

CLASS CERIANTHARIA

A small group of exclusively solitary polyps. They possess a long, muscular, smooth body with a pointed posterior end. At the anterior end lies an expanded oral disc bearing numerous tentacles arranged in two whorls, with the tentacles of the outer whorl being longer (Fig. 100). Cerianthids lack a Skeleton. Their external Morphology is predominantly radially symmetrical, whereas their internal anatomy shows bilateral Symmetry. This is evident in The Structure of the flattened Pharynx, which features a single siphonoglyph and a specific arrangement of septa.

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Fig. 100. General appearance of the cerianthid Cerianthus sp. (after Naumov et al.)

These animals typically burrow vertically into the substrate and encase themselves in a mucous tube reinforced with discharged nematocyst threads. The tubes are usually 30-40 cm long, though tubes of up to 1 m in length are known.

Only the upper extremity of the animal protrudes from the tube; the outer tentacles spread out and rest against the substrate, while the shorter tentacles of the inner whorl are held upright. Cerianthids are typically brightly colored.