Short Notes on Aschelminthes

Aschelminthes

Aschelminthes is basically a phylum of some animals that are no longer related to each other but are from obsolete phyla of pseudocoelomate. Previously there were many classifications in this phylum but now the classifications themselves are from other phyla or are reclassified. Their body actually possesses a pseudocolor. Few related animals from this phyla form the phylum Aschelminthes which consists of animals from ten different invertebrate phyla. Roundworms are commonly included in this phyla. They are also referred to as nematodes or nemathelminthes because their bodies are round when examined transverse cross section-wise. They follow a bilateral symmetry and triploblastic in their body pattern. They may be parasitic or non-parasitic, aquatic or terrestrial. There are many species of roundworms, Ascaris, Wucheria, Rhabditis present in this phylum. The common thing among all of them is the presence of a false coelom. The parasites in this phylum cause a number of diseases.


Characteristics of Aschelminthes

Aschelminthes have the organ-system level of organization. The organs associate to form a distinct system concerned with a specific physiological function such as respiration, digestion, circulation, excretion, and reproduction. They are triploblastic animals. Ascaris and guinea worm are phylum aschelminthes examples. Aschelminthes possess the pseudocolor and hence are called pseudocoelomates. They possess a body cavity but it is not linked with the mesoderm. In between the endoderm and ectoderm mesoderm is present. They have an elongated cylindrical body that tapers at both ends. The digestive system in aschelminthes is complete and has two separate openings. The alimentary canal is a straight tube extending from the mouth at one end to the anus at another end of the body. They have a well-developed muscular pharynx Their food mainly consists of blood, lymph, partially or fully digested food particles which are sucked by the rhythmic pumping action of the muscular pharynx. 

 

Excretion in Aschelminthes

An excretory tube is present in the body of aschelminthes. It helps in the process of excretion in roundworms. This excretory tube collects the body waste from the body cavity and removes it out through the pore. The roundworms thus possess anus as well excretory pore, unlike the other lower animals that come below them. The phyla lower to them lacks digestive tract. 

 

Sexes in Aschelminthes

It is short notes on aschelminthes sexes. Sexes are separate in aschelminthes. Separate sexes mean that males and females can be identified by external features. This condition is also known as dioecious. Females in this case are longer than males. Sperms and ova are produced by different individuals. Only sexual reproduction takes place. In aschelminthes external fertilization takes place. Ascaris and guinea worms have these characteristics. They are examples.

 

Short Notes on Aschelminthes Development

The development of the young ones takes place by intermediate larval stage whereas some develop directly. When direct development occurs, the young ones resemble the adult. The larva is not involved in direct development. There we can conclude that in roundworms both direct and indirect development takes place. 

 

Phylum Aschelminthes Examples

  1. Ascaris

It is commonly called roundworm and is a very common endoparasite in the small intestine of man. It is more common in children than in adults. Their body is covered with syncytial epidermis. They possess a cuticle that is resistant to the digestive enzymes of the host. Its body wall is made up of the following layers: 

  • The cortex is made up of keratin. It is resistant to enzymes. 

  • Matrix is present below the cortex. Below this, there are fibers that are made up of collagen. Below fibers, we have a basement membrane. And below the basement membrane, they have a syncytial epidermis below which only longitudinal muscles are present and circular muscles are absent. 

The sexes in Ascaris are separate and they show sexual dimorphism. Females are longer than males. Males possess a curved tail, two pineal setae, and cloaca. The males have 50 pairs of pre-anal papillae and 5 pairs of postanal papillae. Both males and females have terminal mouths. Their mouth is also triradiate, surrounded by three denticulate lips which are one median dorsal and one ventrolateral. Cuticular lips are present in the mouth. Their lip's inner margin has denticles and the outer margin has sensory papilla. The mid-dorsal lip bears two minute double papillae while each ventrolateral lip bears towards its ventral side a double papilla and towards the lateral sides a single papilla and a special reduced papilla known as amphid. The excretory pore is situated mid ventrally which is a little behind the mouth. There is a single huge excretory cell called renette cell or gland cell in the H-shaped canal system. It consists of two longitudinal excretory canals connected anteriorly by the transverse canalicular network. The Female has a posterior transverse anus and separate gonopore situated ventrally at about \[\frac{1}{3}\] distance from the anterior end. Fertilized eggs of Ascaris pass out of the body of the host through fecal matter. Ascaris is monogenetic which means that no intermediate host is required for its development. The egg is oval in shape with three protective coverings. The coverings are the outer protein layer, middle chitinous shell, and the inner membrane made of esterified glycosides. Infective eggs of Ascaris remain viable for six years. Its zygote will develop into a juvenile within 10-14 days in soil. The larva is called rhabdoid for its close resemblance to rhabditis.  

  1. Dracunculus Medinensis

It is commonly called guinea worm. It occurs in the subcutaneous tissue of man. The toxic secretions of the parasite cause blisters on the skin of the host. It is a digenetic parasite. The human being is its primary host and cyclops is the intermediate host. Sexes are separate. The Female is long while the male is short. The parasite causes itching, diarrhea, nausea, and vomiting. This worm has been completely eradicated from India. These two are phylum aschelminthes examples.

FAQs on Short Notes on Aschelminthes

1. List the main characteristics of Aschelminthes.

Aschelminthes are pseudocoelomate metazoans which means they don’t have the characteristic of a true coelom which is the presence of a cellular peritoneal lining in the coelom. The main characteristics of Aschelminthes are as follows:

  • They have a fluid-filled cavity in their body

  •  They have an underdeveloped vascular system

  •  The body is muscular with longitudinal fibers.

  • They may be parasitic or free-living in aquatic and terrestrial conditions.

  • They have a false coelom and is triploblastic

  • They have a developed digestive system with mouth, intestine, anus and pharynx.

  •  Absence of respiratory and circulatory systems.

  • The nervous system consists of nerve rings with longitudinal nerves on both anterior and posterior sides.

  • Presence of developed sense organs in form of pits, bristles, eyespots, and papillae.

  • They have separated sexes and conduct sexual reproduction.

  • Eggs are shelled but they don’t have the larval stage.

2. What are the main classifications of Aschelminthes?

Aschelminthes is primarily classified into 5 classes. They are Nematoda, Nematomorpha, Rotifera, Gastrotricha, Kinorhyncha. However, there are several orders under these five classes. The details classification are as follows:

  • Orders under Nematoda: Enploidea, Dorylaimida, Mermithoidea, Chromadoroidea, Araeolaimoidea, Money Asteroidea, Desmoscalecoidea, Rhabditoidea, Rhabdias Idea, Oxyuroidea, Ascaroidea, Strongyloidea, Spirurida, Dracunculoidea, Filarioidea, Trichuroidea, Dioctophyma Idea

  • Orders under Nematomorpha: Gordioidea, Nectonematoidea

  • Orders under Rotifera:  Seisonidea, Bdelloidea, Monogonontea

  • Orders under Gastrotricha: Macropodidae, Chaetodontidae

  • Orders under Kinorhyncha: Homalorhagida, Cyclorhagida.

3. Name some of the diseases caused by Aschelminthes.

Some of the aschelminthes are parasitic and some are non-parasitic. The parasitic ones cause diseases in the intestine mainly except for Trichinosis which infects skeletal muscles. They are as follows:

  • Enterobiasis caused by pinworm enters the host body through ingestion of eggs

  • Ascariasis caused by pinworm enters the host body through ingestion of eggs

  • Ancylostomiasis caused by hookworm enters the host body through the skin

  • Trichuriasis caused by whipworm enters the host body through ingestion of eggs

  • Strongyloidiasis caused by whipworm enters the host body through the skin

  • Trichinosis caused by whipworm enters the host body through ingestion of encysted intermediate hosts.

4. Why is Aschelminthes obsolete?

Aschelminthes is presently just an informal name for metazoans from ten classes of invertebrates. The phylum consists of wormlike invertebrates of microscopic size. Previously five classes were included in this phylum but now each of these classes has been reclassified into separate phyla. The animals were originally grouped together under this phylum because all of them have one thing in common that is the presence of a false coelom i.e a coelom that does not possess a lining of mesoderm within it though evolutionary they are not linked to each other. This phylum has some similarities with the arthropods even exhibiting molting. Thus they are not linked to each other by a common phylum and hence the phylum of aschelminthes is obsolete now.

5. Where is this topic of aschelminthes included in the school-level syllabus?

CBSE has included the topic of Aschelminthes in the curriculum of Class 11 biology. It is included in the NCERT book prescribed for CBSE. The PDF of this chapter of the NCERT biology book is available on the website of Vedantu which can be downloaded easily free of cost from the site and also from the Vedantu learning App. Question and answers of this chapter and also that from NEET Exemplar are also given in Vedantu. The solutions have been done by the biology experts of Vedantu. Live classes are also available for the students for any kind of assistance.

6. Name Any Two Examples of Phylum Aschelminthes.

Two examples are Ascaris and guinea worm.

7. What Type of Coelom is Present in Aschelminthes.

They possess pseudocoelom

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