INVERTEBRATE ZOOLOGY IN THREE VOLUMES - VOLUME 1 - H.Y. Shcherbak - 1995

SUBKINGDOM MULTICELLULAR ANIMALS (METAZOA)

SECTION TRUE METAZOANS (EUMETAZOA)

PHYLUM CTENOPHORES (CTENOPHORA)

CLASS AMPHILINOIDEA (AMPHILINOIDEA)

This is a small Class of Flatworms (comprising only ten species) that, in their adult stage, parasitize the body cavity of sturgeons, certain teleost Fishes, and turtles. Crustaceans serve as intermediate hosts in The life cycle of amphilinids.

Representatives of this class are characterized by an unsegmented body possessing a single set of reproductive Organs. The anterior end bears a small retractile proboscis, while the posterior end features a depression that houses chitinoid larval hooks, which are remnants of the cercomer (Fig. 171).

The tegument of amphilinids resembles that of cestodes, yet it lacks microtriches. The internal Structure is generally similar to that of cestodes. A Digestive System is absent, and the excretory system is of the protonephridial type; however, unlike all cestodes, the flame Cells contain not a single tuft of cilia, but many—from 13 to 30.

The FEMALE Reproductive System consists of an irregularly shaped Ovary, oviduct, ootype, Vagina with a seminal receptacle, vitellaria, and a long, convoluted Uterus. The external opening of the vagina is located laterally at the posterior end of the body near the male genital pore, whereas the uterine opening is situated at the anterior end. The Male Reproductive System consists of numerous small Testes, vasa efferentia, and vasa deferentia that lead into an ejaculatory duct with a male genital pore at the posterior end of the body. This opening is provided with specialized Muscles whose contraction ejects seminal fluid into the vaginal opening of another individual.

Fig. 171. Amphilina foliacea:

1 — uterine opening; 2 — testes; 3 — uterus; 4 — vasa efferentia; 5 — vitelline duct; 6 — female and 7 — male genital pores; 8 — vas deferens; 9 — ootype; 10 — ovary; 11 — vitellaria

A decacanth larva, known as a lycophore, develops within the fertilized egg of amphilinids. Lycophores are not released into the Water; instead, intermediate hosts become infected by ingesting the parasite's eggs. To release the eggs containing lycophores from the host's body, some species (such as Amphilina) utilize the host's openings (abdominal pores), while others pierce the host's body with their anterior end and extend the uterus through this opening to discharge the eggs into the water. Various amphipods serve as intermediate hosts for Amphilina foliacea, a parasite of sturgeon fishes. A larva hatches from the ingested egg and migrates into the crustacean's body cavity, where it transforms into the next developmental stage corresponding to the cestode procercoid; however, unlike the latter, it lacks a cercomer and bears chitinoid hooks located directly at the posterior end of the body. Further development of A. foliacea takes place in the definitive host, which feeds on crustaceans infected with procercoids; these migrate into the host's body cavity and develop into adult worms.