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The liver fluke is a parasitic worm that can live in the liver, gallbladder and bile ducts of humans, as well as other vertebrates. The liver fluke causes a disease called fascioliasis. In its structure, the liver fluke is similar to the ciliary worms, but its main distinguishing feature is that it is a parasite. Liver fluke systems have the following features:
Digestive system of the liver fluke
The mouth opening of the liver fluke is located on the front of the body. The mouth looks like a sucker, from which a muscular pharynx departs. The pharynx is followed by the esophagus, and then the branched intestine, which ends blindly. There are many branches from the intestines. The mouth opening also serves as an anus for the worm, through which it removes the products of its own vital activity.
Integuments of the body and the locomotive apparatus of the liver fluke
The liver fluke reaches a length of 30-50 mm, and a width of 12 mm. The body is formed by a skin-muscular sac, and the outer cover is represented by neodermis. Neodermal cells fuse with each other to form syncytium. Beneath the neodermis is the basement membrane, followed by a layer of smooth muscle. Worms have longitudinal, annular and diagonal muscle fibers.
In order to attach themselves inside the body of their final host, worms have special suckers. In the liver fluke, this sucker is represented by a powerful muscular apparatus, which is located on the peritoneum. An additional sucker is the mouth, however, with its help, the parasite also provides nutrition, while the abdominal sucker serves only for fixation.
The body of the liver fluke has a leaf-like shape. Its front end is drawn and resembles a beak in shape. The leaf-shaped body allows you to fully supply the body of the worm with useful substances.
The reproductive system of the liver fluke
The liver fluke is a hermaphrodite. The male genital organs are represented by two testes and vas deferens, ejaculatory canal and copulatory organ. The testicles of the worm are strongly branched. Male sex cells are formed in the testes, then through the vas deferens enter the copulatory organ, which protrudes and penetrates into the vagina of another parasite during mating.
The female genital organs are represented by oviducts with ovaries, vitelline glands, uterus and genital cloaca. Thanks to the yolk glands, the egg receives nutrients. Cross seeding, that is, this process requires the fusion of germ cells of different individuals. The eggs mature in the uterine cavity. After fertilization, the egg is covered with a dense shell. Melis bodies take part in its formation, which secrete a special liquid secret.
Worms during fertilization unite in pairs and exchange male sex cells. They enter the uterus, then into the ootype (the central chamber of the female reproductive system), where they merge with the eggs. The formed egg enters the uterus and gradually moves towards the external genital opening. At this time, an embryo is formed inside the egg. When it matures, the egg comes out. It has an oval shape, yellowish-brown color and sizes from 135 to 80 microns. For the exit of the larva, each egg is equipped with a small lid.
Excretory system of the liver fluke
The excretory organs are represented by a well-developed protonephridial system, which performs the functions of distribution and osmoregulation. In the middle of the body of the liver fluke lies the main excretory canal. The breakdown of complex substances into simpler ones in the body of the parasite is carried out anaerobically.
The nervous system of the liver fluke
The appearance of the nervous system of the liver fluke resembles a lattice, which originates from the peripharyngeal nerve ring. 3 pairs of trunks depart from it, which are interconnected by small jumpers. The lateral nerve trunks of the parasite are better developed.
Some organs of the liver fluke are simplified in structure, for example, it completely lacks a circulatory system.
The main aromorphoses of worms of this species are in the following features:
The presence of suction cups.
Well developed reproductive system.
Complex life cycle of worm development.
Intensive reproduction at almost all stages of the life cycle.
In addition to the fact that parasites lack a circulatory system, they do not have sensory organs in their sexually mature form. However, in the larval form (at the miracidium stage), the worms have eyes and cilia, which allow the parasites to navigate in the external environment and move actively.
For full development from a larva to an adult, the liver fluke will need to change one intermediate host. It is a freshwater mollusk, after which the larva becomes invasive and can infect humans or animals.