INVERTEBRATE ZOOLOGY IN THREE BOOKS - BOOK 1 - H.Y. Shcherbak - 1995

SUBKINGDOM MULTICELLULAR ANIMALS (METAZOA)

SECTION EUMETAZOA (TRUE METAZOA)

PHYLUM CTENOPHORA

CLASS GNATHOSTOMULIDA

Over 80 species of gnathostomulids are currently known. These are widespread marine animals of very small size (0.3–0.5 mm). Their body is elongated, with the HEAD and tail regions usually distinct from one another (Fig. 142). The integumentary epithelium is ciliated, with each Cell bearing a single flagellum.

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Fig. 142. Class Gnathostomulida (Gnathostomula paradoxa):

1 — Pharynx with cuticular jaws; 2 — intestine; 3 — Ovaries; 4 — seminal receptacle; 5 — Testes; 6 — copulatory organ

The excretory system appears as primitive protonephridia arranged in two rows along the sides of the body. Each of them consists of a monociliated cyrtocyte and another cell that forms the protonephridial canal.

The Nervous system consists of a cerebral ganglion and longitudinal cords. Sense Organs are represented primarily by monociliated sensilla.

The Reproductive System in these animals is primitive; sperm ducts and female efferent ducts are absent. The copulatory organ varies in its degree of development among different species.