INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

DIVISION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERAL (BILATERIA) ANIMALS

SUBDIVISION DEUTEROSTOMES (DEUTEROSTOMIA)

PHYLUM HEMICHORDATES (HEMICHORDATA)

Exclusively marine benthic animals that cannot tolerate even the slightest decrease in salinity. They include both solitary burrowing forms and attached sessile species that form peculiar colonies. Around 100 extant and over a thousand extinct species have been described.

Hemichordates are bilaterally symmetrical coelomate animals characterized by the presence of a so-called stomochord—a short, blind, elastic outgrowth of the entodermal Pharynx—as well as paired metameric gill slits connecting the gut to the external environment.

The coelom is tripartite. The alimentary canal is complete, featuring a well-developed Circulatory system with an organized Blood flow driven by the pulsation of a closed pericardial sac. The Nervous system is represented by a continuous nerve plexus with concentrations of Nerve Cells forming dorsal and ventral cords.

Hemichordates are dioecious, with Gonads developing in the trunk region. Fertilization is external. Development proceeds via metamorphosis.

The phylum Hemichordata includes two classes.

Last update: 13/08/2026

Editorial and Educational Adaptation: This material has been compiled based on the primary/original source text. The project team performed an editorial review, corrected technical inaccuracies, structured sections, and adapted the content for an educational format.

What was processed:

elimination of formatting defects (OCR errors, structural breaks, corrupted characters);
editorial organization of content;
standardization of terminology in accordance with academic sources;
verification of factual statements against the original source text.

All mentions of the author, publication year, and origin of the primary text have been preserved in accordance with the source.