BABASAHEB BHIMRAO AMBEDKAR UNIVERSITY Department of Zoology Lecture Outline /Summary Notes CLASS: M.SC. Zoology, 2nd Semester PAPER CODE & NAME: ZL-203-Parasitology -1 Course TeaCher: Dr. Suman Mishra TOPIC- UNIT3: Morphology and Anatomy of Parasites-1 CESTODA/ CESTOIDEA TAXONOMIC POSITION CLASS CESTODA/ CESTOIDEA SubClass Cestodaria SubClass EuCestoda Order Amphilinidea Order GyroCotylidea Order Caryophyllidea: in freshwater fish e.g. Amphilina e.g. Gyrocotyle Order Spathebothriidea: Fresh /marine fish Order ProteoCephalata Order Tetraphyllidea e.g.Acanthobothrium Order Diphyllobothridea e.g. Diphyllobothrium Order TrypanorhynCha e.g. Tetrarhynchus Order Pseudophyllidea e.g.Bothriocephalus Order CyClophyllidea e.g. Taenia GENERAL CHARACTERISTICS Highly speCialized Class of flatworms of Phylum Platyhelminthes, the members are Commonly Called tapeworms. It has 3,500 speCies. They are ribbon-shaped, dorsoVentrally flattened (tape-like) organisms laCking epidermis, body CaVity, skeletal and circulatory systems. DigestiVe system is absent, or when present it is rudimentary and without anus. Nutrition is obtained through body surfaCe from the intestine of host. NerVous system and exCretory system are present. Body is segmented exCept Order Caryophyllidea . All cestodes are exClusiVely endoparasites and adults liVe in the Vertebrate digestiVe system while juVeniles (larVal forms) are found in both Vertebrate and inVertebrate hosts. The members mostly exhibit a high degree of host speCifiCity. They are predominantly hermaphrodites with well deVeloped reproductiVe system. They haVe indireCt life CyCles with need of atleast one intermediate host. These parasites liVe in digestiVe traCt of Vertebrates as adults, and in bodies of Various animals as juVeniles (larVa). MORPHOLOGY The adult body is diVided into three main regions. 1. Head (Scolex): It is present at one end and is a hold-fast struCture. It may haVe grooVes, CirCular or leaf like suCkers, and rostellum armed with hooks and hooklets. The tapeworm firmly anChors itself to the intestinal wall with the SColex. Mouth is not present in them. 2. NeCk: The scolex narrows to form the neCk from whiCh strobilization i.e. formation of new proglottid segments ocCurs in this region. As new proglottids are formed from the neCk region, they push the older ones progressiVely posterior, thus creating a chain of proglottids - the strobila. The asexual proCess of forming segments is termed strobilation. 3. Strobila : It is the third body region Consisting of a series of linearly arranged proglottids. Proglottids funCtion primarily as reproduCtiVe units. The stroblia Can be subdiVided into 3 regions: Immature, Mature and GraVid proglottids. Anterior proglottids are immature, while posterior proglottids are mature and produCe eggs.. After fertilization, the proglottids at the posterior end accumulate eggs and are called gravid (ripened). HOLD FAST ORGANS The sColex loCated at anterior end funCtions as Hold fast organs, serVing for attaChment to host tissues and Consist of suCkers, grooves, and rostellum with spine like hooks and hooklets. Three types of suCkers are present on sColex: 1. Bothria- 2, rarely 4/6 shallow sucking grooVes (Pseudophyllidea) 2. Bothridia: 4 leaf like flexible struCtures (Tetraphyllidea) 3. True suCkers/acetabula-4 musCular Cups, with or without hooks (CyClophyllidea). Hooks are generally grouped at apiCal end of sColex on a protrusible rostellum Bothria Acetabula Bothridia NERVOUS SYSTEM The nervous system consists of “brain” whiCh is a reCtangular or CirCular nerVous tissue Varying in complexity from a simple ganglion to a combination of several ganglia and Commissures. Several pairs of longitudinal nerVe Cords extend posteriorly from this “brain” along the length of the strobila, lateral to the osmoregulatory Canals. The longitudinal nerVe Cords are ConneCted in each proglottid by Cross connectives. Small motor nerVes emanating from the Cords and Cross-connectives innervate the reproduCtiVe organs and musCulature. Small sensory nerVes supplying the tegument merge with the cords and connectives EXCRETORY SYSTEM/OSMOREGULATION A protonephridial system also runs the length of the tapeworm. It Consists of 2 Components: the collecting canals and the flame cells. The collecting canals (2 dorsal and 2 Ventral) are aligned on lateral side and extend the entire length of the strobila. All 4 Canals lie just inside the medullary margin of the parenchyma, and a single transVerse Canal ConneCts the Ventral Canals at the posterior end of eaCh proglottid. The Ventral Canals Carry fluid away from the sColex, while the dorsal Canals carry towards scolex thus helping to effiCiently remoVe wastes from body. In some tapeworms, the 4 longitudinal canals are linked within the scolex by either a network of canals or a single ring of vesicles whereas in others, the dorsal and Ventral Canals on eaCh side are linked by a simple connection in the region of the scolex, with no apparent exchange between the 2 sides. In the terminal proglottid of young worms, there is an exCretory VesiCle into whiCh the Ventral Canals empty; In older tapeworms, the posterior ends of the Ventral Canals open independently to the exterior. Flame Cells are assoCiated with the Ventral canals; fluid connected by the flame cells passes through secondary tubules into the main canals. Analysis of fluid within the osmoregulatory system shows that it consists primarily of: gluCose, soluble proteins, lactic acid, urea, and ammonia ULTRASTRUCTURE OF TEGUMENT Body wall The outer body wall of tapeworms Consists of a tegument that bears speCialized miCrovilli known as miCrothriCes (singl. miCrothrix) projeCting from its outer surfaCe. These tips proVide resistanCe to the peristaltiC movement of the host’s intestine and agitate intestinal fluids in the immediate miCrohabitat. The tapeworms have no digestiVe system, therefore tegument plays an important role in nutrient absorption. The tegument even absorbs some of the host’s own enzymes whiCh help in digestion. Tegument Consists of following layers: • A syncytial epithelium, with distal and proximal CytoplasmiC regions. • Tegumental musCulature made of 2 layers - an outer circular and an inner longitudinal musCle layer • GlyCoCalyx – covering tegument and made up of Carbohydrate Containing moleCules, for proteCtion from host digestiVe enzymes & enhanCing nutrient absorption Nutrition: LaCking a digestiVe tract, these worms must deriVe all nutrient molecules from the host or its miCrohabitat, and suCh moleCules must Cross the tegument. Nutrients cross the tegument by actiVe transport, faCilitated diffusion, and simple diffusion. The most important nutrient moleCule is glucose, whiCh after polymerization within the parasite, is stored as glyCogen usually in the parenChyma and interstitial fluid; the only other major, transported Carbohydrate is galaCtose. The tapeworms reside in enVironments of Very low oxygen tension (small intestine), thus obtain energy anaerobiCally by substrate phosphorylation Via glycolysis. Most adult tapeworms also absorb lipids, probably by simple diffusion. MetaboliC rates differ in different parts of the body with neCk and immature proglottids haVing a muCh higher rate of metabolism than the mature and gravid proglottids. FUNCTIONAL ANATOMY OF MALE & FEMALE REPRODUCTIVE ORGANS Tapeworms are monoeCious. They produCe large number of eggs. Each proglottid Contains a Complete set of male and female reproductiVe organs. MALE REPRODUCTIVE SYSTEM consists of numerous testes scattered throughout each mature proglottids, vas efferens arising from each testis whiCh unite to form a Common vas deferens, a musCular, eVersible cirrus modified from distal portion of Vas deferens, and usually enClosed in a cirrus pouch. Cirrus pouch opens into Common genital atrium . The testes produCe sperms which are conducted into the Copulatory organ Cirrus through a duCt system. In most speCies there is an enlarged area of the Vas deferens, the seminal VesiCle, for the storage of sperm. The male system of a proglottid matures before the female system (protrandry), therefore, Copulation ocCurs with another mature proglottlid of the same tapeworm or with another tapeworm in the same host. Thus, cross fertilization produces hybrid Vigor. FEMALE REPRODUCTIVE SYSTEM consists of a single, sometimes bilobed ovary, leading into an oViduCt whiCh opens into the ootype surrounded by Mehlis’ gland. The ootype reCeiVes a single Common vitelline duct formed by union of many primary vitelline ducts whiCh arise from the vitelline glands. The vitelline glands (=Vitellaria) may form a CompaCt body or Consist of numerous folliCles sCattered throughout the medullary parenChyma in each proglottid. The oViduCt Continues as the uterus whiCh opens to the outside of the proglottid through a uterine pore for expelling eggs (Order. Pseudophyllidea) or is a blind saC (Order CyClophyllidea) whiCh aCCumulates the deVeloping eggs. The vagina carries sperms from genital atrium to the oViduCt. Sperms are stored in an enlargement of the Vagina called seminal receptacle. The oVary produCes eggs whiCh are fertilized in the region where the Vagina and oviduct join. Then eggs pass into the ootype where capsules are formed around the eggs through secretions from the Vitelline gland. The ootype is also surrounded by the Mehlis’ gland whose seCretion helps in the formation of the egg Capsule. The reproduCtiVe organs degenerate after storage of egg. Therefore, gravid proglottids are called as “bags of eggs”. In speCies