INVERTEBRATE ZOOLOGY IN THREE VOLUMES - VOLUME 3 - H.I. Shcherbak - 1997

PHYLUM CHAETOGNATHA, OR ARROW WORMS

Arrow worms are marine animals, the vast majority of which lead a pelagic lifestyle. They possess an elongated, bilaterally symmetrical, often transparent body divided into HEAD, trunk, and tail regions. The Mouth is located at the anterior end of the ventral side of the head, surrounded by a robust grasping apparatus. Fins are situated along the sides and at the posterior end of the body (Fig. 122).

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Fig. 122. Sagitta euxina

The body is covered with a thin cuticle and a single-layered epithelium, which thickens in certain areas due to The formation of multilayered regions. Adult animals possess a primary body cavity, although a coelom is established during embryonic development.

The digestive tract is a straight tube terminating in an anus at the boundary between the trunk and tail regions.

Specialized excretory, respiratory, and circulatory systems are absent. The Nervous system consists of a Brain (supraesophageal ganglion), several small ganglia in various PARTS OF THE body, a robust ventral ganglion, and rather long connectives uniting them.

Arrow worms are hermaphrodites; their development proceeds without metamorphosis.

The phylum Chaetognatha includes a single class of the same name.



Last update: 13/08/2026

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