INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE METAZOA (EUMETAZOA)

SECTION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERAL (BILATERIA) ANIMALS

SUBSECTION SPIRALIA (SPIRALIA)

PHYLUM FLATWORMS (PLATHELMINTHES)

SUBPHYLUM NEODERMATA (NEODERMATA)

SUPERCLASS CERCOMEROMORPHA (CERCOMEROMORPHA)

CLASS GYROCOTYLIDA (GYROCOTYLIDA)

A small group of Flatworms (10 species) that parasitize chimaeroid fish.

Morphology. The body is flattened, leaf-shaped, with scalloped margins (Fig. 136). A spherical or pear-shaped sucker is located at the anterior end, while the posterior end features a specialized attachment apparatus resembling a folded rosette.

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Fig. 136. Gyrocotyle fimbriata (adapted from Poljansky):

1 - cuticular spines; 2 - ganglion; 3 - scalloped body margins; 4 - nerve trunks; 5 - shell glands;

6 - nerve ring; 7 - attachment rosette; 8 - sucker; 9 - Vagina opening; 10 - vagina; 11 - Testes;

12 - Uterus sac; 13 - uterus; 14 - seminal receptacle; 15 - Ovary; 16 - ganglion of the attachment rosette

On the DORSAL SIDE OF the anterior part of the rosette, at the border with the trunk, There is a small funnel-shaped invagination at the bottom of which larval hooks are retained in sexually mature individuals.

The tegument of gyrocotylids is covered with microvilli, the tips of which are elongated into slender whip-like appendages. Glandular Cells are located beneath the tegument of the attachment rosette; their secretion is released to the exterior and presumably facilitates better attachment of the parasite to the host Tissues. In some species, the tegument at the anterior end of the body bears robust cuticular spines. Two Muscle layers lie beneath the tegument: circular and longitudinal.

The Digestive System is absent. The excretory system is represented by protonephridia; excretory pores are located in the anterior third of the body. The Nervous system is of the orthagon type. Sense Organs are poorly developed and appear as isolated sensilla.

The Reproductive System is hermaphroditic. The FEMALE REPRODUCTIVE SYSTEM includes a small ovary located in the posterior half of the body. The duct of the seminal receptacle, numerous shell glands, and the vagina—which opens externally on the dorsal surface of the body—all empty into the short oviduct. A convoluted uterus originates from the oviduct, with its opening located ventrally in the anterior half of the body. The Male Reproductive System consists of numerous small testes predominantly in the anterior part of the body, vasa efferentia, a vas deferens, and a poorly developed copulatory organ whose opening is situated near the uterine opening.

The life cycle is simple, without intermediate hosts. Embryonic development occurs either in the external environment (Water) or as the eggs pass through the loops of the uterus. The fully formed larva—the lycophore—leaves the egg membrane and actively swims. Its elongated body has a ciliated covering. The ducts of unicellular glands open at the anterior end, and 10 hooks are located at the posterior end. Upon entering the host Organism, the larvae lose their ciliated covering, migrate into the fish Circulatory system, and subsequently into the Blood Vessels of the intestinal mucosa. Sexually mature gyrocotylids typically localize within the spiral valve of chimaeras.

Before reaching sexual maturity, these parasites exhibit hyperparasitism—a phenomenon where organisms parasitize the bodies or body surfaces of parasites of the same or other species. Gyrocotylid larvae penetrate the Connective Tissue of young individuals of their own species, where the Initial Stages of metamorphosis take place: a cercomer appears as a small spherical body with radially arranged hooks. Subsequently, young gyrocotylids leave their temporary "hosts" and re-enter the lumen of the chimaera's spiral valve. Their cercomer gradually sinks into the funnel-shaped invagination, its boundaries progressively disappear, and the adjacent body regions proliferate to form the attachment rosette.

All known species of gyrocotylids are classified into two genera: Cyrocotyle (nine species) and Gyrocotyloides (one species).