INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

SECTION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERAL (BILATERIA) ANIMALS

SUBSECTION MOLTING ANIMALS (ECDYSOZOA)

PHYLUM NEMATODES (NEMATODA)

CLASS ENOPLIA (ENOPLIA)

Most species are free-living marine, freshwater, and soil inhabitants, while others are commensals and parasites of animals and plants. The most characteristic feature of enoplians is the presence of well-developed Sense Organs in free-living forms. Based on their feeding habits, they are predominantly predators and saprophages (orders Enoplida, Dorylaimida, Mononchida). In many species, the stoma is armed with sharp onchs, Teeth, or a sharp spear (Fig. 273).

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Fig. 273. Anterior body ends of enoplians (from Paramonov and Sonin, modified):

a - sensory setae in marine enoplians; b, c - oral armature in dorylaimids, plant parasites Hoplolaimus tylenchiformis and Dorylaimus striatus, respectively: 1 - sensory setae; 2 - teeth; 3 - stylet; 4 — spear

Dangerous parasites of humans include Representatives of the order Trichocephalida: the trichina worm (Trichinella spiralis) and the whipworm (Trichocephalus trichiurus). The whipworm parasitizes the human cecum. Its anterior end is elongated into a Hair-like appendage (hence its name), with which it deeply embeds into the intestinal mucosa and feeds on Blood (Fig. 274). Females reach a length of 5 cm. Humans become infected by ingesting invasive eggs from soil, unwashed vegetables, raw Water, etc. In the human intestine, a larva hatches from the egg, penetrates the villi of the Small Intestine using its stylet, and subsequently moves into the lumen of the cecum, embedding its hair-like anterior end into the mucosa. Whipworms can live in the human intestine for up to five years, causing digestive disorders, anemia, and sometimes appendicitis.

Fig. 274. Whipworm Trichocephalus trichiurus (from Dogiel):

1 - expanded posterior end; 2 - hair-like anterior end of the body embedded in the intestinal mucosa

The trichina worm (Trichinella spiralis) causes trichinosis, a disease widespread wherever pig farming is developed, including Ukraine. In addition to humans, trichinosis affects pigs, rodents, insectivores, and carnivorous mammals. Mature trichina worms are small in size: females up to 4.4 mm, males up to 2 mm. The life cycle of the trichina worm takes place entirely within the host's body, without a free-living stage in the external environment (Fig. 275). Infection occurs by eating meat containing trichina larvae. Rats and pigs become infected by eating each other's meat. In insufficiently heat-treated pork, microscopic capsules contain live, spirally coiled trichina larvae. In The Stomach, the larvae are released from the capsules, and within two to three days, the trichina worms reach sexual maturity. After mating, the males die, and after a certain time, the females give birth to live larvae. The offspring of a single female number about 2,000 larvae, which pass through the intestinal walls into the lymphatic and Blood Vessels, migrate through the blood, and are carried to the Muscles, where they penetrate Muscle fibers, feed on their contents, and eventually encyst. Starting from the sixth month, the capsule walls begin to impregnate with calcium compounds, but the larvae remain viable for a long time (sometimes for 20-24 years). Infection of a new host occurs when eating the meat of a previous host infested with trichina larvae. The greatest danger to the host Organism is posed by trichina larvae, which destroy Muscle Tissues and exert a toxic effect on the body. This is accompanied by muscle pain; the settlement of larvae in the eyes can lead to blindness, and in the Brain, to death.

Fig. 275. Life Cycle of Trichinella spiralis:

a - female; b - male; c - larvae in muscles; d - encysted larvae in muscles; e - Circulation of the parasite in the host organism;

f - host range; g - pathways of trichina circulation in the wild; h - in synanthropic conditions:

1 - meat scraps with trichina larvae; 2 - circulation of trichina among rats