Cyclostomata

[¦sī·klō′stō·mə·də]

(invertebrate zoology)

An order of bryozoans in the class Stenolaemata.

(vertebrate zoology)

A subclass comprising the simplest and most primitive of living vertebrates characterized by the absence of jaws and the presence of a single median nostril and an uncalcified cartilaginous skeleton.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Cyclostomata

(also Cyclostomi), a class of lower aquatic vertebrates of the superclass Agnatha. The eellike body is covered with a tough skin, which has many slime-secreting cells. There is no external skeleton. The notochord is persistent, and the internal skeleton is cartilaginous. There are no paired fins. The gills, which are in the form of pouches, are of endodermal origin. The funnel-shaped mouth is supported by a ring of cartilage (hence the name). The teeth are horny, and the tongue is used for perforating. The olfactory organ is sac-shaped, with a nasohypophyseal canal emerging from its bottom and ending in a blind sac. In the membranous labyrinth there are only two semicircular ducts.

The two subclasses of Cyclostomata, Petromyzones (lampreys) and Myxini (hagfishes), sharply differ from one another. Cyclostomata are marine, freshwater, or both. The females deposit eggs which are fertilized and develop in water. Cyclostomes are either ectoparasites of fishes or predators. Some species of lampreys are commercially valuable.

REFERENCES

Berg, L. S. Sistema ryboobraznykh i ryb, nyne zhivushchikh i iskopaemykh, 2nd ed. Moscow-Leningrad, 1955. (Tr. Zoologicheskogo instituta AN SSSR, vol. 20.)
Nikol’skii, G. V. Chastnaia ikhtiologiia, 3rd ed. Moscow, 1971.

V. D. LEBEDEV

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References in periodicals archive

A new species of hagfish, genus Eptatretus (Cyclostomata, Myxinidae), from the Pacific Ocean near Valparaiso, Chile, with new data on E.

Three new species of hagfishes, genus Eptatretus (Cyclostomata, Myxinidae), from the Pacific Coast of North America, with new data on E.

Eptatretus strickrotti n. sp. (Myxinidae): first hagfish captured from a hydrothermal vent

The fine structure of the micropyles of the eggs of Myxine glutinosa and Eptatretus burgeri (Cyclostomata).

Cyclical changes in the testis of the hagfish Eptatretus burgeri (Cyclostomata).

Fine structure of spermatozoa of the hagfish Eptatretus burgeri (Agnatha)

The earlier of these events marked the origin of the class Stenolaemata, of which the Cyclostomata are the only extant order; the later event marked the origin of the order Cheilostomata (of the class Gymnolaemata).

Calcitic nacreous ultrastructures in Bryozoans: implications for comparative biomineralization of lophophorates and Molluscs