INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

SECTION TRIPLOBLASTIC (TRIPLOBLASTICA), OR BILATERALLY SYMMETRICAL (BILATERIA) ANIMALS

SUBSECTION SPIRALIA (SPIRALIA)

PHYLUM GNATHOSTOMULIDA

Marine, microscopic (0.3-0.5 mm in length) interstitial animals distributed globally throughout the World Ocean. Over 80 species are known.

Anatomy. The body is elongated, with distinct HEAD and tail regions (Fig. 149).

Class="center">

Fig. 149. Diagram of the anatomy of Gnathostomula paradoxa (from Joffe):

1 - Pharynx with cuticular jaws; 2 - gut; 3 - Ovaries; 4 - Seminal Vesicle; 5 - Testes; 6 - copulatory organ

Skin-muscular sac. A characteristic feature of gnathostomulids is The Structure of their integumentary epithelium, in which each Cell bears a single flagellum. In addition to a layer of circular Muscles, the skin-muscular sac includes several bundles of striated longitudinal muscles. The parenchyma is poorly developed.

Digestive System. The Mouth opening is located near the anterior end of the body. The pharynx features a pair of hard cuticular jaws (hence the name of the phylum). Anterior to the pharynx lies a hard plate used by the animal to scrape off food—blue-green Algae, fungal hyphae,

and Bacteria. The pharynx leads into a blind-ending, sac-like midgut.

The excretory system is represented by numerous protonephridia arranged in two rows along the sides of the body. Each protonephridium consists of two Cells: a uniflagellated cyrtocyte and another cell that forms the protonephridial canal.

The Nervous system consists of a cerebral ganglion and longitudinal nerve cords located superficially, directly beneath the epithelial layer.

Sense Organs are primarily represented by uniflagellated sensilla.

The Reproductive System is hermaphroditic.

Gnathostomulids are capable of living in anoxic layers of marine sediments, forming dense aggregations (up to 600,000 individuals per 1 m3). A representative species is Gnathostomula paradoxa.



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.