The introductory part gives methodological instructions for working with the determining key, briefly discusses the bionomic zones of the sea, the lifestyle and conditions of invertebrate organisms, gives an idea of ​ ​ the levels of biological organization, indicates the time of existence of taxa and determines their paleogeographic and rock-forming value. A geochronological scale and a scheme of geochronological distribution of the main groups of invertebrate organisms are placed in front of the systematic part.