Here is a term paper on the ‘Characters and Representatives of Aschelminthes’. Find paragraphs, long and short term papers on the ‘Characters and Representatives of Aschelminthes’ especially written for college and medical students.
Term Paper # 1. Characters of Aschelminthes or Nemathelminthes:
1. The animals of this phylum are triploblastic and acoelomate.
2. Their body is vermiform, cylindrical or flat and bilaterally symmetrical.
3. A pair of cuticle is found on the body. It is covered by scales or small bristles.
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4. Their body is un-segmented.
5. The body cavity in them is a pseudocoel.
6. They are always elongated and appear round in transverse sections.
7. The sense organs are found in the form of papillae and amphids. The presence of amphids is a characteristic of the phylum nemathelminthes.
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8. The mouth is present in the middle of the anterior end and is surrounded by lips.
9. A permanent head is not distinct in them. The part of the body behind anus in females in cloaca, in males, it is called the anus.
10. The sexes are separate and the gonads are coiled.
11. The excretory system consists of canal-like or glandular structures but their excretory nature is doubled.
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12. They are oviparous or ovoviviparous.
13. The nervous system consists of a nerve ring from which nerves are given off both anteriorly and posteriorly.
14. Generally, a pair of circular pouches called phasmids is found in parasitic nematodes.
15. They are found in free living condition in the wet marine or fresh water ground. Some members of this phylum are endoparasites.
Characters of Class Nematoda:
1. They are triploblastic and acoelomate animals.
2. Their body is elongated, cylindrical and pointed at both the ends.
3. The body is covered by cuticle.
4. The body is un-segmented and without cilia.
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5. Most of them are fresh water, some are found in soil and a few are parasites.
The class nematoda is divided into two sub-classes:
1. Aphasmidia
2. Phasmodia
Sub-Class—1. Aphasmidia:
1. The sensory organs are not found on the caudal or posterior region of the body.
2. Different types of sense organs are found of the anterior part of the body.
The sub-class aphasmidia is divided into two orders:
1. Chromadoridia
2. Anoplioidea
Order—1. Chromadoridia:
1. The oesophagus is not long and is made up of three regions.
2. The oesophageal glands are never bilobed.
Examples:
Monophstra, Plactus, Chromadora and Cyatholaimus, etc.
Order—2. Anoploidea:
1. The body is divided into two parts, anterior muscular and posterior glandular part.
Examples:
Trichinella, Trichuris, Trichocephala, Capilaria and Mermis, etc.
Sub-Class—2. Phasmidia:
1. Caudal sense organs are present.
2. The sensory organ of the anterior part is like a pore.
The sub-class phasmidia is divided into two orders:
1. Rhabditida
2. Spirurida
Order—1. Rhabditoidea:
1. The oesophagus is formed of three layers which are more distinct in larval stages.
The order Rhabditidea is divided into four sub-orders:
(i) Rhabditina:
Examples – Bunonema and Rhabditis.
(ii) Tylenchina:
Examples – Heterodera and Chondronemma.
(iii) Strongylina:
Examples – Ancylostoma, Necator, Haemonchus and Metastrongylus.
(iv) Ascaridina:
Examples – Ascaris, Enterobius, Toxocara and Thelostoma.
Order—2. Spiruroidea:
The oesophagus is formed of two layers:
The order-spirurida is divided into two sub-orders:
(i) Spirurina:
Examples – Gonglonema, Wuchereria, Onchocera and Loa.
(ii) Camallanina:
Examples – Dracuuculus and Comallanus.
Term Paper # 2. Some Representatives of Aschelminthes or Nemathelminthes:
1. Rhabditis:
The order Rhabditoidea includes many free living semi-parasitic nematodes. They are found in soil, organic substances, water and excreta of man and animals. There is no alternation of generations in them. Rhabditis hominis is mostly found in the faeces of man and Rhabditis maupasi occurs in soil. Their juveniles are found in earthworms.
The adult R. maupasi is about 1.7 to 2 mm long. The excretory system is ‘H’ shaped and the reproductive system is ‘H’ shaped. There is one testes in males and two ovaries, two oviducts and seminal receptacles are found in females.
The uteri are small and valva is situated in the middle of the posterior part of the body. Their life cycle is simple. The eggs, laid in the soil, reach inside the earthworms, through their excretory and genital pores. Here they develop into juvenile stage. After the death of earthworms, they develop into adults on the decaying flesh of earthworms.
2. Heterodera:
It is a phytoparasitic nematode. It is well developed for the parasitic mode of life. It is also known as “sugar beet eel worm”. They infect the sugar beets and plants of cruciferae family. Heterodera rastochiensis is called golden potato eel worm. It infects roots of potato plants. It is also known as root knot eel worm.
Galls and nodules are formed in the roots of the plants by its infection. It infects beans, peas, cabbage and cotton plants. The shape of the male worm is rhabditoid-like. A fully mature female is pyriform in shape.
Its colour is lemon yellow and size varies from 0.6 to 0.75 mm only the females of H. marioni are pathogenic. The roots of the plants are infected by the second larval stages of these worms. Their eggs laid on the vegetables, after destroyed the tissues of the vegetables damage the intestine of man on reaching there.
3. Enterobius Vermicularis:
It is found as a parasite in man throughout the world. It is commonly known as pin worms or ‘seat worm’ or ‘thread worm’. It lives in the vermiform appendix, colon and caecum of man as a parasite. The females are larger in size than the males. There are three small lips and pair of cephalic expansions.
On the anterior end of these worms, the posterior end of the female is pointed but in it is blunt, curved and provided with a spicule. The gubernaculum is not found. The caudal alae support the papillae. The uteri are coiled and filled with eggs. The eggs laiden females migrate to the inner part of the anus of the host.
Their life cycle is simple without an intermediate host. The wriggling egg-laiden females cause itching in prianal and regions at the time of egg laying. The presence of air in the neighbourhood incites the females to lay eggs.
The host scratches the infected part due to itching and in the process the eggs laid by the female stick on the fingers and below the nails and re-infect the host on being swallowed with food or water. The symptoms of the infection of these worms are loss of appetite, occasional hysteria and inflammation of the mucous membrane of colon and appendix.
4. Dracunculus Medinensis:
It is commonly known as ‘guinea worm’ or ‘serpent worm’. Its adults are found in the viscera and tissues of human. This worm is common in Africa, Turkey, India, North America and China.
The shape of the body of the worm is like a thin filament. The female is larger in size than the male. A ring-shape structure made up of cuticle is found at their anterior ends. It contains a mouth, six inner and four outer papillae. The female genital pore is found in the middle of the body.
In males, four pairs of pre-anal and six pairs of post-anal papillae are found. The spicules of males are thin and filamentous. The females lay larvae. They migrate to those parts of the body of the host which come more in contact of water.
In these parts, it produces a toxic substance which produces blisters on the skin. On coming in contact with water, these blisters burst making wounds in the skin, the female projects its uterus to release small coiled embryos in the water.
The female dies after laying the eggs. The released embryos or larvae lead a free swimming life for sometimes and then infect the secondary host, Cyclops of the class crustacea. After moulting twice in Cyclops, the larvae become capable of re-infecting man with the water containing the infected Cyclops. They reach in the body of man again and become adult in sub-cutaneous tissues.
5. Trichinella Spiralis:
The infection of Trichinella does not occur in tropical countries. It is common in Europe, America, and Arctic regions. The parasite is generally found in man, pigs, dogs, seals, whales and polar-bears. The female is larger than the male. In both, the anterior part is pointed and the posterior is fleshy. The cuticle found on them is stripped.
The mouth opens into the pharynx which leads into the capillary oesophagus. The oesophagus is covered by hard granular cells called Stichosomes. Only one testis and one ovary are found in males and females respectively. A pair of copulatory pads is found on the posterior part of the male. The spicule is absent. The vulva is present in the anterior part of the body of the female.
The adult worms are embedded in mucous membrane of the host. The males die after copulation. The female increases in size and lay larvae in villi peritoneum, mesenteric lymph glands and mesenteric veins on reaching the intestine. After 25 days of infection, the larvae reach the arteries through the hepatic and pulmonary filters and settle in striated muscles.
The larvae coil and form a cyst around them in the voluntary muscles. The cysts are generally formed in muscles, eyes, tongue or diaphragm of the host. The cysts are lemon shaped and are formed in about two weeks. The cysts have a nucleated fibrous layer and a hyaline layer. Each cyst contains about 1 to 7 juveniles.
The infection in man takes place by eating improperly cooked or raw meat of infected pigs. In the cysts embedded in human beings, a hard covering made up of calcium is formed around them. Sometimes the larva dies in the calcified condition. Its larvae remain viable for infection for 11 years in pig and 25 to 30 years in man. After reaching the suitable host, the ecdysis taken place in four in five times in larva and it becomes adult.
6. Loa Loa:
It is another filarial parasite found in humans. It is also known as ‘African eye worms’. It is mostly common in Africa. During migration, it generally causes itching and swelling in the eyes. This condition is known as ‘Calabar swelling’.
The body of the parasite is covered with warts. The females give birth to microfilariae which are found in blood circulation only at day time. During night, they are absent from the blood circulation. Their intermediate host a blood sucking fly, after reaching the fly, they become capable of infecting other hosts.
The microfilariae of Loa loa prove fatal for a blood sucking fly. After reaching the fly, they become capable of infecting other hosts.
The microfilariae of Loa loa prove fatal for the host on reaching the brain and spinal cord. They give much trouble to the host by causing swelling and pain in the eyes.
7. Trichuris Trichiura:
The common “human whip worm” is Trichuris trichiura. It has a world-wide distribution, particularly in the warmer parts. The worm occurs in the caecum, appendix vermiform and intestine embedded between villi or even penetrated into the mucous layer. The slender body ranges from 30 to 50 mm in length, the female being slightly longer than the male.
The anterior two-third part of the body containing the pharynx or oesophagus, is extremely thin, like a whip, hence the popular name. This whip like portion anchors the worm to the wall of the host’s intestine. It feeds an epithelial cells and blood. Life cycle is monogenetic i.e. no intermediate host.
After copulation female lays eggs in lumen of intestine. Development occurs in most soil and infective larva develops in three weeks within the egg. Man is infected due to contamination of food and water. Hatching taken place in intestine and within one year the juvenile grows into adult.
8. Tococara Canus (Dog Ascarid):
Larvae hatching from eggs ingested by a pregnant female dog migrate through placenta to enter the developing embryos or foeti puppies born may show a heavy infection of these worms. Adult individuals generally have fewer worms. Adult male and female worms each up to ten and twenty cm respectively.
Eggs start development in host’s faeces and become infective in 4 or 5 days. When ingested, they hatch in the new host’s intestine to liberate juvenites.
They penetrate the intestinal wall, reach lung through hepatic portal circulation break into alveoli, migrate up the air passage, become swallowed in pharynx and reenter intestine. Dog acarid is also important medically. Embryonated eggs in contaminated soil may be ingested by children, especially during the dirt eating stage, when children are one to three year old. Larvae known as larva migrans, continue to live in liver of infected children indefinitely.
9. Wuchereria Bancrofti (Filaris Bancrofti):
Its body is thread like which tapers anteriorly with a slightly swollen point end. There are no lips, the pharynx is muscular anteriorly and glandular posteriorly. The adult nematodes live in the lymphatic vessels and lumph glands, lying in coils. The female is 10 cm long and 0.25 mm in diameter.
The male is 4 cm by 0.1 mm, its tails is coiled like a tendril with many papillae, and with one long short spicule. The mature female gives birth to juveniles known as microfilariae, each of which is enclosed in a delicate sheath. The microfilariae pass from the lymphatic system into blood vessels, they come to the peripheral circulation between 10 pm and 2 am but disappear inside during the rest of the day.
The microfilariae will develop further only if they are sucked up along with human blood by a mosquito. Accumulation of living and dead Wuchereria blocks the lymphatic system which results in an inflammation of lymph glands and other pathological conditions.