Tapeworms

Tapeworms (Cyclophyllidea Braun, 1900), an order of tapeworms, many representatives of which parasitize humans. The scolex of tapeworms is equipped with four cross-located suckers, and in some species also a rostellum armed with hooks. The body of tapeworms in the vast majority of cases is characterized by well-expressed strobilation. The ovary is most often bilobed, the vitelline gland is ordinary, usually located behind the ovary. The uterus represents a closed sac of various structures. Due to the absence of an uterine opening, eggs can exit from the proglottid only after the violation of its integrity or its complete disintegration. Tapeworm eggs do not have a lid. Their outer shell is extremely delicate and often equipped with filaments. Inside the egg there is a spherical or ellipsical embryo, called an oncosphere, surrounded by an embryonic membrane. The oncosphere is characterized by three pairs of embryonic hooks. The number of testes in tapeworms varies from one to several hundred in each proglottid. The male reproductive system ends with a genital pore located next to the vaginal opening on the lateral edge of the strobila. Less frequently both openings are located on the same plane. Some representatives of tapeworms are characterized by the doubling of the reproductive system in each proglottid. The larval stage of the parasite - a larvocyst - most often has the structure of a cysticercus or cysticercoid, less frequently of a cenurus or echinococcus. Tapeworms are hermaphrodites with the exception of the genus Dioicocoestus Fuhrm. Compared to other orders of tapeworms, tapeworms differ in the greatest diversity of their anatomical structure and abundance of species. Among tapeworms that affect humans, the largest number of representatives also belongs to the order of tapeworms. The order of tapeworms is divided into the following 9 families according to Meggitt's classification (1924) with modifications by Skryabin and Shultz (1929): 1) Acoleidae Ransom, 1909; 2) Mesocestoididae Fuhrmann, 1907; 3) Tetrabothriidae Linst, 1891; 4) Davaineidae Fuhrmann, 1907; 5) Amabiliidae Fuhrmann, 1908; 6) Taeniidae Ludwig, 1886; 7) Hymenolepididae Raill. et Henry, 1909; 8) Anoplocephalidae Cholodk., 1902; 9) Stilesiidae Skrjabin, 1926. In humans, representatives of the following 4 families parasitize: A. Davaineidae. The rostellum of the scolex is armed with characteristic hammer-shaped hooks. Usually the suckers are also armed with small numerous hooks. The genital openings of proglottids are either double or ordinary (genus Raillietina). The mature uterus disintegrates into capsules containing one or several (Raillietina) eggs. A representative of this family, namely Raillietina asiatica Linst., 1901, was found in humans only once in Ashgabat. B. Anoplocephalidae. The scolex is unarmed. The width of mature segments significantly exceeds the length. Vitelline glands and Meline's body are present. Eggs are equipped with a pear-shaped apparatus. The parasitism in the human intestine of a representative of this family, Bertiella satyri (Blanch., 1891), has been confirmed in tropical countries. C. Hymenolepididae. The scolex is usually armed. Testes are mostly located behind the glands. The uterus is sometimes sac-like, sometimes reticular, sometimes disintegrating into capsules. Mature proglottids are usually square. Medical importance is attached to 3 representatives of this family, belonging to the subfamilies: Hymenolepidinae Ransom, 1909, and Dipylidiinae Stiles, 1896, namely: 1) Hymenolepis diminuta (Rud., 1819), 2) Hymenolepis nana (v. Sieb., 1852) (see Hymenolepis), 3) Dipylidium caninum L., 1758 (see). D. Taeniidae. The scolex is either unarmed or equipped with a double crown of hooks. The length of mature proglottids significantly exceeds the width. The genital openings are irregularly alternating. The uterus has the appearance of a longitudinal trunk with lateral branches or lateral protrusions. The larval stage has the structure of a cysticercus, cenurus, or echinococcus (see Cysticercosis, Cenurosis, Echinococcus). Lit.-see ref. to art. Flatworms. I. Podolyapolskaya.