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 It might be outdated or ideologically biased.



a subclass of annelid worms of the class Polychaeta (some zoologists classify Myzostomida as a separate class). Myzostomes are commensals or parasites of echinoderms (sea lilies, starfish, and ophiurids). Their parasitic way of life has led to the simplification and alteration of body structure (as compared with the structure of typical annelids). The oval or discoid body is from 0.5 to 12.5 mm long. On the ventral side of the body are five pairs of processes, or modified parapodia. The processes terminate in hooklike bristles, by means of which the worms attach themselves to the animal host. Myzostomes have a poorly developed brain and no eyes. The excretory organs are metanephridia (usually one pair). There are no circulatory and respiratory systems. Myzostomes are hermaphroditic: the male sex glands mature first, and the female glands later. A larva, the trochophore, emerges from the fertilized egg.

There are seven families of myzostomes, comprising about 120 species, distributed primarily in tropical and subtropical seas. In the USSR six species are found in the Barents, Kara, and Bering seas, as well as in the Sea of Okhotsk and the Sea of Japan. Some myzostomes are motile and crawl rapidly on the body of the animal host; others remain near the host’s mouth opening or penetrate the intestine. Some of the worms are found in the integuments of the arms and disk of the host, forming characteristic cysts.


Rukovodstvo po zoologii, vol. 2. Moscow-Leningrad, 1940.
Traite de zoologie: Anatomie, systematique, biologie, vol. 5, fasc. 1. Paris, 1959.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Among animals, there were Mesozoa, Gnathostomulida, Bryozoa, Cycliophora, Myzostomida, and Nemertea; also there are Rotifera, Nematomorpha, Scalidophora, Acanthocephala, Entoprocta, and Gastrotricha from Coelomata.
Myzostomida: a link between trochozoans and flatworms?
Volume 4A Polychaeta, Myzostomida, Pogonophora, Echiura, Sipuncuba.
Kleptoparasitism, the diversion of host food to a parasite that does not otherwise damage the host, is well known in some birds, mammals, and terrestrial arthropods (e.g., Elgar, 1993; Vickery and Brooks, 1994; Carbone et al., 1997), and even in one terrestrial gastropod (Zamora and Gomez, 1996), but it is poorly documented among marine invertebrates, with the exception of annelids in the order Myzostomida (Eeckhaut et al., 1995).