INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

SECTION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERAL (BILATERIA) ANIMALS

SUBSECTION SPIRALIA (SPIRALIA)

PHYLUM FLATWORMS (PLATHELMINTHES)

SUBPHYLUM NEODERMATA (NEODERMATA)

SUPERCLASS CERCOMEROMORPHA (CERCOMEROMORPHA)

CLASS AMPHILINIDA (AMPHILINIDA)

A small group of parasitic Flatworms (only 10 species known, with one species, Amphilina foliacea, found in Ukraine) that inhabit the body cavity of sturgeons, certain teleost Fishes, and turtles as adults. Crustaceans serve as intermediate hosts. They are distributed worldwide across all continents (except Antarctica), predominantly in tropical and subtropical regions.

Anatomy. Amphilinids have a flattened, mostly leaf-shaped body. A small depression at the anterior end contains a mobile proboscis connected to the ducts of numerous glandular Cells. The posterior end features a depression that houses chitinoid larval hooks.

The body wall is represented by a tegument. The Digestive System is absent. The excretory system is of the protonephridial type, and The Nervous system is an orthogon. The Reproductive System is hermaphroditic (Fig. 137).

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Fig. 137. Amphilina foliacea (adapted from Dogiel):

1 - uterine pore; 2 - Testes; 3 - Uterus; 4 - vas deferens ducts; 5 - vitelline duct;

6, 7 - female and male genital pores, respectively; 8 - vas deferens; 9 - ootype; 10 - Ovary; 11 - vitellaria

The life cycle of amphilinids involves alternating hosts. Species parasitizing the body cavity of sturgeon fishes (such as A. foliacea or A. japonica) release their eggs externally through the abdominal pores of the definitive host, whereas species inhabiting the body cavity of teleost fishes or turtles, which lack abdominal pores, exit by disrupting the host's body wall. Eggs containing a fully formed ciliated larva, known as a lycophore, are released into the Water. The posterior end of the lycophore bears 10 chitinoid hooks, while its anterior end features the openings of unicellular gland ducts.

The larva does not hatch from the egg in water; instead, intermediate hosts become infected by ingesting the eggs. For A. foliacea, the intermediate hosts are amphipod crustaceans (genus Gammarus and others).

Upon hatching in the intermediate host's gut, the lycophore migrates into the body cavity, where the next larval stage develops. This stage corresponds to the procercoid of cestodes (see below), but it lacks a true cercomer. The hooks are located directly on the posterior part of the body. Definitive hosts become infected by consuming intermediate hosts. The parasites then migrate through the gut wall into the definitive host's body cavity, where they reach sexual maturity.