INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

DIVISION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERAL (BILATERIA) ANIMALS

SUBDIVISION CHAETOGNATHA

PHYLUM CHAETOGNATHA

Chaetognaths are exclusively marine, active predators with an elongated, transparent body. Their HEAD bears a characteristic set of grasping spines (hence the name of the phylum).

Chaetognaths are striking for their unique combination of a simple body plan and highly specialized Tissues. They lack excretory, circulatory, and respiratory systems, as well as genital ducts; however, their epidermal epithelium is multilayered in certain areas, their musculature is striated, their fins contain elastoidin—a protein otherwise typical of fish and cyclostomes—and they possess a highly developed Nervous system.

Chaetognaths are characterized by radial Cleavage, deuterostomous development, and enterocoelous Formation of the mesoderm.

All these features previously provided grounds for classifying them as deuterostomes; however, other characteristics set them apart as a unique animal group. During embryonic development, they form a coelom that is absent in adults. Molecular genetic studies also refute the hypothesis of a close phylogenetic affinity between chaetognaths and deuterostomes.

The phylum Chaetognatha includes a single Class.



Last update: 13/08/2026

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