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(invertebrate zoology)
A group of shell-bearing mollusks represented by few living forms; considered to be a sixth class of mollusks.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a class of marine mollusks. Until 1952 they were known only from fossil shells from deposits of the Lower Paleozoic. In 1952, Danish zoologists discovered the first modern representative of Monoplacophora—Neopilinagalatheae. The body consists of a head, a foot, and a visceral hump covered with a mitriform or flat-spiral shell lined with a mantle. The head and foot can retract into the shell by means of one to eight pairs of muscles. Between the mantle and the foot is a mantle groove, in which there are five or six pairs of feathery gills; into the groove open the ducts of six pairs of kidneys and the anal opening. The digestive system includes an esophagus with a radula, a loop-shaped gut with a stomach, and a paired liver. The heart consists of two ventricles and four auricles. The nervous system consists of four longitudinal cords united by an esophageal ring and transverse commissures. There is an organ of equilibrium—the statocyst. There are two pairs of sex glands; the sexes are separate.

Of the approximately 60 original species of Monoplacophora, six are extant. They are united in the genus Neopilina. Extinct forms from the Cambrian to the Devonian are grouped in three orders: Tryblidiida (miter-shaped forms with many body retractors; Neopilina are included here), Cyrtonellida (flat-spiral or miter-shaped forms with two pairs of retractors), and Sinuitopsida (flat-spiral forms with one pair of retractors).


Beklemishev, V. N. “K voprosu o rannei evoliutsii molliuskov.” Zoologicheskii zhurnal, 1958, vol. 37, issue 4.
Dogel’, V. A. Zoologiia bespozvonochnykh, 5th ed. Moscow, 1959.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Cyrtolites Conrad, 1838 and its position among the Monoplacophora (Mollusca).
Relationship and internal structure of a new Pilina (Monoplacophora) from the late Ordovician of Oklahoma.
The taxonomic position of Cyrtonella mitella (Hall) (Mollusca, Monoplacophora).
The Solenogastres (= Neomeniomorpha), Caudofoveata (= Chaetodermomorpha), and Polyplacophora were grouped in the subphylum Aculifera, and the Monoplacophora, Bivalvia, Gastropoda, Scaphopoda, and Cephalopoda were placed in the subphylum Conchifera.
Bacterial symbionts in the epidermis of an Antarctic neopilinid limpet (Mollusca, Monoplacophora).