(1859 A.D.) created Nemathelminthes and Grobben (1910 A.D.) introduced aschelminthes.
It includes about 15,000 species.

VVI Examples of Phylum Nemathelminthes for Entrance Exams:-
  • Ascaris lumbricoides (Roundworm)
  • Ancyclostoma duodenale (Old World Hookworm)
  • Necator americana (New World Hookworm)
  • Loa loa (Eye worm)
  • Trichuris (Whipworm)
  • Enterobius vermicularis (Pin Worm or Threadworm or Churna)
  • Wuchereria bancrofti (Filarial worm)
  • Dracunculus (Guinea worm)
  • Trichinella

General characters of Nemathelminthes

1. Pseudocoelomate (Blastocoelomate) i.e. the body cavity is not lined by embryonic mesoderm and false coelom derived from embryonic Blastocoel.
2. Cylindrical and Bilaterally symmetrical i.e. body can be equally divided into two parts, has the syncytial epidermis.
Epidermal cells lack cilia. The body is circular in cross-sections so-called roundworms.
3. Triploblastic i.e. three germ layers; ectoderm, mesoderm, and endoderm.
4. Unsegmented, muscle layer of body wall consists of longitudinal fibres only. Circular muscle absent.
5. Vermiform- worm-like, elongated, cylindrical, tapers at both ends.
6. Organ–system grade of body organization
7. Complete digestive tube, with a mouth and anus/cloaca, non-muscular intestine.
8. Presence of cuticle that secretes anti-enzymes to protect the worm from the digestive enzymes of the host.
9. Excretion occurs by gland cells or canals or both. Some forms have protonephridia or Renette cells or Giant cells.
Renette cell is ‘H’ shaped. They are ammonotelic or ureotelic.
10. Respiratory system absent, aerobic-free living, anaerobic- parasites, gaseous exchange through the general body surface.
11. Circulatory system absent, circulation by hydrolymph or pseudocoelomic fluid.
12. Aquatic, terrestrial, parasites, or free-living found in soil or water. Some are important plant and animal parasites.
13. First unisexual phylum, No asexual reproduction, sexual dimorphism, internal fertilization, males are smaller.
14. Nervous system with a nerve ring and anterior and posterior nerves.
15. Usually direct development without a larval stage.
They are more advanced than Platyhelminthes in having body cavity, unbranched and complete digestive tract, and separate sex; cylindrical body.

Classification of Phylum Nemathelminthes

On the basis of the presence or absence of phasmids (caudal sense organs), phylum Aschelminthes is divided into two classes namely, Aphasmidia and Phasmidia.

Class 1: Aphasmidia
· No phasmids
· Various types of anterior sense organs (amphids), rarely pore-like.
· Excretory organs are either reduced or absent.
· Most of them are free living.

Example: Enoplus, Mermis, etc

Class 2: Phasmidia
· Presence of phasmids
· Amphids are pore-like.
· Excretory organs consist of well-developed paired lateral canals
· Most of them are parasites.

Example: Ascaris, Trichuris, etc

Class 3: Rotifera
· Commonly called wheel animalcules having a trunk and tail.
· Body wall thickened into plates or lorica.
· A ciliated tracheal disc is present which helps in ingestion and locomotion.
· Sensory organs antenna and eyespot.

Examples: Limnias, Branchionus, Rotara, etc.

Class 4: Nematomorpha
· Commonly called hairworms.
· Free-living and aquatic with separate sexes.
· Body wall with thick cuticle.
· Body cavity is filled with parenchyma.
· Larva is found as a parasite in the insect.

Examples: Paragordius, Nectonema, etc.

Class 5: Gastrotricha
· Free living.
· Microscopic, maybe marine or freshwater forms.
· Mouth surrounded by bristles.
· Body wall with cuticle which bears spine.
· Posterior end forked.

Examples: Chaetonotus, Macrodasys etc.

Class 6: Kinorhyncha
· Marine, microscopic, and worm-like forms.
· Superficial segmentation of the body.
· Body surface with spiny cuticle and spherical.

Examples: Trachydemus, Echinoderes, etc.

Trichinella spirallis

· Commonly called Trichina worm
· Smaller and slender parasitic nematode in human, pig, dog, cat, rat
· Infection is caused by ingestion of encysted larvae with raw or undercooked flesh. In the intestine, cysts dissolve and larvae are liberated. They become adults within 2 days. They survive only for a week or two but encysted larvae retain viability for several years. Copulation occurs in the intestine and female lays eggs that hatch and the resulting young larvae enter the bloodstream and are carried to the voluntary muscles of the chest and legs. Here they get coiled and form cysts.
· Causes trichinosis characterized by abdominal and muscular pains, nausea, and diarrhoea.
· Piperazine citrate has been found effective in the removal of adult worms from the intestine

Trichuris trichiura

· Commonly called whip-worm, as the anterior portion of the body is long and slender, posterior portion thickens giving the appearance of a bullwhip,
· Adults live in the large intestine of the man, particularly in the human colon, also in the vermiform appendix and rectum.
· Females lay an enormous number of eggs daily that pass in stools. Eggs gain entry into the human body with contaminated drinking water and raw fruits and vegetables. In the intestine, the eggs hatch, and larvae develop into adults. The infective stage is the 2nd stage embryonated eggs
· Sanguivorous i.e., feeds on a blood meal
· Symptoms are bloody stools, pain in the lower abdomen, weight loss, nausea, vomiting, constipation, fever, headache, appendicitis, anaemia, eosinophilia, etc.
· Causes trichuriasis
· Drugs like mebendazole or albendazole are most effective when administered orally for 3 consecutive days.

Loa loa

· Commonly called African eye-worm or loa-worm, chiefly found in Africa
· Causative agent of Loiasis or “Calabar swellings”
· Adults live in the subcutaneous tissues of the body and migrate freely across the eyeball beneath the conjunctiva, hence the name eye-worm.
· Digenetic parasite, Intermediate hosts are mango flies- Chrysops dimidia or Chrysops silica
· Females produce microfilariae. They show diurnal periodicity. Larvae moult and develop up to the infective stage in fly and are again infected in the bloodstream of man through the proboscis. It causes intense itching, pain, and swelling in eyes known as “Calabar swellings”.

Dracunculus medinensis

· Commonly called Guinea worm
· Largest or longest nematode parasite in human
· Common digenetic parasite of the subcutaneous tissue of man throughout the warmer parts of the world
· Mature female contains numerous embryos in her uterus. The egg-laying female worm goes to hands, feet, legs, etc that regularly come in contact with cold water. Here the parasite produces toxic secretions which produce blisters on the skin. Soon an ulcer is formed. On coming contact with water, the ulcer breaks down and the worm releases embryos in water. Larvae, after swimming freely for a short time, penetrate the body of Cyclops. In Cyclops, the larva moults twice and becomes infective in 3 weeks’ time. When infected Cyclops is taken in by a man with water, the larvae escape and bore their way into subcutaneous tissue where they become adults. Within the subcutaneous tissue, the favourite areas of the parasites are arms, shoulders, and legs forming blisters. So, one can feel the worm by touching the skin.
· Larvae are released in the stomach.
· Guinea worm infection causes non-specific symptoms like itching, eosinophilia, nausea, vomiting, diarrhoea, asthma, fainting, etc.
· Metronidazole is the drug of choice.
· Oil of Chenopodium is used successfully for expulsion.

Taxonomic summary

Phylum- Nemathelminthes

Ascaris- Common roundworm
Ancylostoma- Hookworm
Necator- Hookworm 
Enterobius- Pinworm or seat worm
Wuchereria- Filarial worm
Dracunculus- Guinea worm
Loa loa- Eye worm
Trichuris- Whipworm
Trichinella- Trichina worm

Disease-causing Roundworms of man

Name Habitat Effect
Ascaris lumbricoides (The Giant intestinal roundworm) Small intestine Anaemia, Diarrhoea, Bronchitis, Pneumonia
Ancylostoma duodenale (The Hookworm) Intestine Itching and Inflammation of skin, Anaemia, Mental and physical retardation
Trichinella spirallis (The Trichina worm) Encysted larvae in striated muscles, adults in the intestine Trichinelolosis, Muscular pain, Pneumonia
Wuchereria brancofti (The Filarial worm) Lymphatic vessels, Lymph nodes Elephantiasis or Filariasis Lymphatic obstruction (Lymphoedema, hydrocele, elephantiasis)
Dracunculus medinensis (The Guinea worm) The subcutaneous tissue of limbs Ulcers, Diarrhoea, Asthma, Giddiness, Eosinophilia
Enterobius vermicularis (The Pinworm) Large intestine, caecum, and appendix Oxyuriasis, Anal itching, Appendicitis, Nervous trouble
Trichuris trichiura (The Whip worm) Caecum, appendix, and colon Trichuriasis, Abdominal pain, Anaemia, Bloody stools
Loa loa (Eye worm) Subcutaneous connective tissue of eyes Conjunctivitis, Calabar swellings

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