Parasatic adaption of helminths and its phylogenetic significance.

Parasitic adaptions of helminths:

Helminths are the group of invertebrates organism which includes animals belonging to two important phyla namely,platyhelminths and nemathelminths.Several species of the group helminths have adapted themselves to the parasitic mode of life A parasite is that organism which lives at the expense of another organism, at the expense of another organism, and in return, it cause injury or harm to the host.Such as association in which one organism, the parasite, is benefited while the another one the host, is harmed is called parasitism. Parasitism has evolved accidently as a result of contact between different forms of animals,mainly for the purpose of obtaining nourishment and receiving shelter. An ideal parasite is that which harm to its host because if the host dies the parasite depending upon the will also have to die.

According to the Elton, "the union of parasite and host is usually an elaborate compromise between extracting sufficient nourishment to maintain and propagate too much the vitality or reducing the number of its host which is providing it with a home and free ride."

To lead a parasitic mode of life, the parasites have adapted themselves in such a way as to survive and adjust itself ith the body environment of their host.Adoption is a dynamic process of adjustment with the new environment for establishment, self-regulation, self-preservation and race continuation.

Herbert Spenser defines adoption as "the continuous adjustment of internal reaction to external reaction". The degree of adaptations exhibited by different types of parasites mainly depends on upon their intimate relationship with their host. These adaptations are mainly two types give
as

1. Morphological adaptations:

2. Physiological adaptations:

Thus, adaptation is the fitness of the organism to its environment. It is the characteristics with results in suitable and convenient morphological and functional correlation between an organism and its environment.

These adaptations are termed Parasitic adaptations in such case , are of morphological as well as physiological nature. A parasitic flatworm has undergone profound adaptations to suit their parasitic mode of life.

Morphological adaptations

Several morphological adaptations have occurred in the body of helminths parasites in order to survive well in the body of their host. They have occurred either in the form of degeneration of certain organs or attainment of new organs.

a) Degeneration of organs:

In order to lead a parasitic life complete or partial degeneration or loss of organs have taken place in the body of helminth parasites. Such degeneration is important organs in which degeneration have occurred are -

1) organs of locomotion: since the parasite resides in the host body where they live well protected and nourishment readily available, there is no need to move. Hence, the locomotory organelles are completely loss. However, in cases where the larval forms are free living, the locomotory organs in the form of cilia reappears, e.g, Miracidium larva of Fasciola.

2) Tropic organs: The organs which are concerned with nutrition are called tropic organs. As the parasite derives fully digested or partially digested nutrition from the host's body, the alimentary canal has either totally disappeared (e.g. degree of degeneration, Ascaris).

3) Nervous system and sense organs: The endoparasite live in a well protected and more or less stable environment inside host's body in perpetual darkness, there is no need of a complex form of the nervous system, consequently, the photoreceptor organs (eyes) and other sense organs have completely lost. The central and peripheral nervous system have also reduced considerably as compared to the other free-living species of the same phylum.

b) Attainment of new organs:

The helminths parasites have attained certain special structures which help them adjust well within the body of their host. These are-

1) The shape of the body: The shape of the body have become round or dorso-ventrally flattened or ribbon-like which enable them to fit in the space of host's body where they reside.

2) Development of the protective covering: The integument of the parasite have lost epidermis and have developed several layered thick protective covering of cuticle. The cuticle is resistant to host's digestive enzymes, antitoxin and abrasive action of the food and roughage passing through the digestive tract. The cuticle is permeable to water and also help in the absorption of food protective spines have also developed in the cuticle of several trematodes.

3) Development of adhesive organs: The endoparasites live in an environment where there is always a danger of being dislodged or swept away along with the host's body fluid or peristalsis of the alimentary canal. Hence, there is always a demand for certain organs of attachment to keep the parasite in their respective position. The different forms of adhesive organs found in helminth parasites are-

i) Acetabulum: In adult flatworms, in the upper half of the body, the acetabulum is present which act as anchoring structure e.g. Fasciola.

ii)Suckers: Suckers are strong organs or attachment found in both trematodes as well as in cestodes In Fasciola hepatica, there are two suckers, an anterior sucker surrounding the mouth and a large ventral sucker. In a Taenia solium, there is four sex.Hooks: The anterior end of the body of cestodes and trematodes bear hook and spines as

Hooks: The anterior end of the body of cestodes and trematodes bear hook and spines as the organ of attachment.

iv) Jaws: In nematodes (e,g.Ascaris) chitinous jaws are present inside the mouth which helps them to anchor with the wall of the gut.

(v) . Glands.: The secretory glands are present at its near to the mouth. In the case of certain helminth help them to tissue by secreting histolytic juices.

Physiological adaptation:

The helminths endoparasites live in the body in the physiological environment of the host.

These helminths have acquired certain physiological adaptations. Some of these physiological adaptation exhibiting by parasites are Secretion of anti-enzymes and mucous, Development of anaerobic mode of respiration, Osmotic pressure adaptability, Chemotaxis,

Protective mechanism.

1.Secretion of anti-enzyme and mucous: In order to obtain the nutrition from host's body most of the endoparasite live in the host body where abducent nutrient is also available.But in such time, the parasites living inside the gut are always in danger of being digested by the digestive enzyme of the host. The parasite (e.gTaenia solium)overcome these problems by developing following adaptation.

a) Development of strong impermeable cuticle around the parasite.

b) The parasite stimulates the host gut to the secret huge amount of mucous that surround the parasite.It also protection from the digestive juice of host.

c) Most of the parasite produce anti-enzyme which protects from the gastric juice and digestive enzymes of the host.

d) It has been reported that lime cells present in the body wall of the tapeworm neutralize the acidic effect of gastric juice.

2. Development of anaerobic mode of respiration.

Most of the helminths endoparasites especially those living inside the gut lumen live in the oxygen-deficient environment.At the same time, they possess very low metabolic rate which requires very little amount of oxygen. To overcome this problem of not- availability of oxygen, helminth es parasites have adapted to the anaerobic mode of respiration in which energy is obtained by fermentation of glycogen bin an oxygen free environment and carbon dioxide and free fatty acid are given out as the end product.

3. Osmotic pressure adaptability.

The para sites maintain osmotic pressure of their body fluid approximately same or slightly

less than that of the environment in which they live inside the body of the host cell. They facilitate them to absorb the nourishment from the general body surface. Osmotic equilibrium also prevents the disturbing exchange of water.

4. Chemotaxis:

The endoparasite has t0 face the changing chemical environment inside the body of their hosts, hence are adapted to exhibit the phenomenon of chemotaxis which allows them to find their way and respond accordingly.

5. Protective mechanism: Alimentary canal parasites have to protect themselves from the action of the digestive juice of host.Helminth accomplishes

this by following action which is listed below.

1. by the stimulating wall of the gut to secrete mucus, which then form a protective clothing around the parasite.
2. by secreting anti-enzymes to neutralize the digestive system of the host and,
3. by probable continually renewing their protective.

Phylogenetic Significance:

Plathelminthes have supposed to be evolved from a coelenterate-like ancestor which undergone change following

from radial to bilateral symmetrical, Coelenterata ancestor was like a planula larva as primitive acoel worms that may characteristic with planula, such as listed

1. Absence of epidermal basement membrane,
2. Absence of gut,
3. Absence of gonads,
4. The absence of excretory organ.

Reference:

Aggarwal Sarita. A Text Book of Biology,New Delhi.: Madhuban Educational Books, 2011.

Bhamrah, H.S., and Kavita, Juneja. A Text Book of Invertebrates, New Delhi: Anmol Publications Pvt Ltd, 2011.

Jordan E.L. and P. S., Verma. Invertebrate Zoology, New Delhi,: S. Chand and Company Pvt. Ltd., 2011.

Kotpal, R. L..,Modern Text Book of Zoology: Invertebrates, New Delhi, India: Rastogi Publications,2011.

http://www.parasitesinhumans.org

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