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In the absence of free oxygen, energy is obtained by the process of fermentation of glycogen, in which by glycolysis it is broken down into CO 2 and fatty acids.
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But the manner of O 2 liberation from food is not yet clearly known. Thus, respiration is anaerobic, which consists of extracting oxygen from food-stuffs-they absorb and assimilate through their cuticle. Cestodes have well-developed water osmoregulatory systems and their pH is also high.Īs intestinal parasites lead their life in an environment completely devoid of free oxygen (O 2), evolutionary adaptations have resulted in a very low metabolic rate requiring a minimum amount of oxygen. The osmotic pressure in the interior of the parasitic worms remains less than or same to the host, so that there is no difficulty in exchange of water. The flukes feed on tissue elements and inflammatory exudates and have probably intracellular digestion. Physiologically Helminths show striking adaptation to lead the parasitic life in the body of the host and to enjoy their life in simplest ways. Parasites can be described as being solely adapted for reproduction. Cestodes, for example, basically consist of a small head and neck region and the rest is serially repeated gonads. In many parasites there is a tremendous elaboration of the reproductive organs, associated with increased gamete production. The longitudinal lateral canals are provided with a number of flame cells (Fig. The characteristic feature of excretory vessel in Cestoda is ladder like. Excretory system particularly in Nematodes exhibits very little adaptation to parasitic mode of life. Ladder-like nervous system is the characteristic feature of Platyhelminthes (Fig.
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The advantage is that the worms can get pre- digested nutrients of the host. Similarly due to specialised musculature, power of locomotion enables the roundworms (Ascaris sp.) to counteract gut peristalsis and to maintain their position in the intestine. The well-developed musculature in Tapeworms (Taenia sp.) helps them to distribute their elongated snake like bodies throughout the length of the intestine of the host. Presence of spinous integument-in many Trematodes. In gut parasites, however as in Tapeworms, Gnathostomes, Amphistomes and Nematodes-the cuticle becomes thick, impregnated with impermeable chitin like substances and enzyme resistant, so that it is not digestable by the digestive juices of the host but is permeable to water. The parasites live in rich nutritious environments such as liver- flukes (in bile), blood flukes (in blood), Sporocyst larva and Cysticercus (in vertebrate muscles) and other larval forms (developing in lymph spaces and blood stream). The cuticle becomes thin, partly or wholely for food absorption. The cuticle of Helminth is highly modified and adapted to resist against digestive juices and for adhesion. Cyst membrane forms around the body, e.g., Metacercaria larva of liver-fluke. In parasites and particularly in endoparasites there is loss of locomotory organs. (iii) Loss of cilia from the body surface is an indication in this direction. (ii) Ectoparasites are capable of some free movement but endoparasites have little to do so when detached from the host, Nematodes are the obvious exception to the trend of flattening in parasites and parasitic nematodes, as a whole, show little morphological specialization.Īs the adult parasites live for entire life in the body of the host, the locomotor-organs are usually not necessary for them.Ĭonsequently the locomotor-organs are completely reduced except in the free-swimming larval forms: Fleas are laterally flattened and rely on escape through the hairs. Most parasites are dorso-ventrally flattened and this is related to the need to cling on to the host. This could be related to increased egg production. Many parasites are large compared with their free-living relatives.