INTRO TO NEMATODES AND NEMATODES 1

• Somatic Musculature


  1. One or more layers of longitudinally arranged muscle cells: somatic musculature

  2. Probing and penetrating motion
• Body Wall layers

  • Cuticle
  • Hypodermis
  • Somatic Musculature
• Digestive Tract components

  • Foregut: Mouth, Pharynx, Esophagus
  • Midgut: Intestine
  • Hindgut: Cloaca (Male), Subterminal Vent
• Layers of the Cuticle


  • Epicuticle: thin, protective barrier that contains glycocalyx
  • Exocuticle
  • Mesocuticle: with obliquely oriented, collagenous, fibrous sublayers that can shift angles of orientation, thus, providing flexibility to the cuticle
  • Endocuticle: fibrous layer but orientation of fibers is indistinct
• Aphasmids

  • Trichinella spiralis
  • Trichuris trichiura
  • Capillaria philippinensis
• Reproductive organs: sexes are separate (dioecious), some are parthenogenetic, males are smaller than females, males are curved posteriorly, females are flat posteriorly
• Mechanoreceptors types

  • Labial papilla: lips surrounding the mouth
  • Cephalic papilla: behind the lips
• Hypodermis


  1. Thin, cellular structure that secretes the cuticle

  2. Protrudes into the pseudocoelom along the mid-dorsal, mid-ventral, and lateral lines to form the longitudinal hypodermal cords where the hypodermal organelles are confined

  3. Lateral cords: excretory canal

  4. Dorsal and ventral cords: longitudinal nerve trunks
• Cuticle


  1. Covered by tough, elastic protective covering: cuticle

  2. Metabolically active and periodically undergoes molting

  3. Also lines buccal cavity, esophagus, rectum, cloaca, vagina, and excretory pore
• Phasmids

  • Hookworms
  • Ascaris lumbricoides
  • Strongyloides stercoralis
  • Enterobius vermicularis
  • Filarial worms
• Chemoreceptors types

  • Amphids: anteriorly located
  • Phasmids: posteriorly located
• Nematode

  • Common name: roundworm
  • Elongated and cylindrical in shape, with bilateral symmetry
  • Non-segmented
  • Rounded anterior end; tapered posterior end
  • Light cream-white in color
• Male Reproductive Organ


  1. Single tubule

  2. One or two testes at its smaller end

  3. Extends into a vas deferens and seminal vesicle

  4. Terminates in an ejaculatory duct opening into the cloaca
• Pseudocoelom is a cavity that contains fluid called hemolymph which bathes the internal organs, offers protection by acting as a cushion, and acts as a hydrostatic skeleton providing support and rigidity
• Nervous System

  1. 2 major nerve centers

  2. Circumesophageal commissure or nerve ring

  3. Ganglia from longitudinal nerves

  4. Rectal commissure

  5. Ganglia from ventral longitudinal nerve
• Mode of Transmission

  • Ingestion of embryonated egg: Ascaris lumbricoides, Trichuris trichiura, Enterobius vermicularis
  • Ingestion of infective larvae: Capillaria philippinensis, Trichinella spiralis, Parastrongylus cantonensis
  • Skin Penetration: Hookworms, Strongyloides stercoralis
  • Mosquito-borne: Wuchereria bancrofti, Brugia malayi
  • Inhalation: Enterobius vermicularis, Ascaris lumbricoides
  • Autoinfection: Capillaria philippinesis, Strongyloides stercoralis, Enterobius vermicularis
• Female Reproductive Organ


  1. Usually didelphic

  2. Two cylindrical ovaries which expand into uteri

  3. Uteri unite to form a common vagina

  4. Single gonophore or vulva

  5. Opening of the reproductive organ to the exterior

  6. Frequently located near the middle of the body

  7. Varies in position between species

  8. Oogonia: being fertilized in the spermatheca
• Parthenogenetic


  • Males are smaller than females
  • Males are curved posteriorly
  • Females are flat posteriorly
• Habitat of Adult Worms in Hosts

  • Small Intestine: Ascaris lumbricoides, Capillaria philippinensis, Hookworms, Trichinella spiralis, Strongyloides stercoralis
  • Large Intestine (Colon): Trichuris trichiura (rectal prolapse), Enterobius vermicularis (pruritus ani)
  • Tissue: Trichinella spiralis, Filarial worms, Dirofilaria immitis, Gnathostoma spinigerum
  • Larva Migrans in Man: Dracunculus medinensis, Angiostrongylus cantonensis, Ancylostoma caninum, Ancylostoma brazilense
• Molting

  1. Formation of new cuticle

  2. Loosening of the old cuticle

  3. Rupturing of the old cuticle

  4. Escape of the larva

  5. Exsheathing fluid: control the sequence of events of molting
• Molting

  Hypobiosis: Developmental arrest, lag phase at some stage of development – life cycle is temporarily arrested, adaptation
• Excretory System

  1. Renettes: Basic component of the excretory system

  2. Large unicellular gland that empties through an excretory pore

  3. Not yet conclusive if it functions for removal of wastes like ammonia or strictly osmoregulatory
• Male Reproductive Organ

  1. Single tubule

  2. One or two testes at its smaller end

  3. Extends into a vas deferens and seminal vesicle

  4. Terminates in an ejaculatory duct opening into the cloaca

  5. One or more chitinized copulatory spicules

  6. Gubernaculum: guides the spicules when extended

  7. Sperm has no flagella or acrosomes
• Adult Worm

  • Adult female: oviparous, viviparous (larviparous), parthenogenetic
  • Oviparous: most of the nematodes produce egg, and the young hatches after being expelled from the body
  • Viviparous: brings forth live young that have developed inside the body of the adult female nematode
  • Parthenogenetic: development of a female (rarely a male) gamete (sex cell) without fertilization, asexual reproduction
• Larval Forms
• Larval Forms


  1. Rhabditiform Larva: First stage larva of Strongyloides stercoralis and hookworms, esophagus has terminal esophageal bulb

  2. Filariform Larva: L3 of Strongyloides stercoralis and hookworms, long esophagus, no terminal bulb, usually infective stage to the definitive host

  3. Microfilaria: Prelarval form of filarial worms
• Molting

  1. Formation of new cuticle

  2. Loosening of the old cuticle

  3. Rupturing of the old cuticle

  4. Escape of the larva

  5. Exsheathing fluid: control the sequence of events of molting
• Molting

  Hypobiosis: Developmental arrest, lag phase at some stage of development – life cycle is temporarily arrested, adaptation
• Hookworms


  • Long esophagus, no terminal bulb
  • Usually, infective stage to the definitive host
• Molting

  1. Hypobiosis

  2. Developmental arrest

  3. Lag phase at some stage of development – life cycle is temporarily arrested

  4. Adaptation to withstand adverse environmental conditions while waiting for the host
• Ascaris lumbricoides


  • Common names: Giant intestinal round worm, Biggest nematodes infecting humans, Pink worm, Pink color when well-nourished, Most common intestinal nematode of man, Soil-transmitted helminth (STH) along with Trichuris trichiura and hookworms
• Ascaris lumbricoides contributes to malnutrition and impairment of cognitive performance, reduces work capacity and productivity in adults
• Epidemiology factors


  • Cosmopolitan distribution
  • 1.2 billion people globally affected
  • 2,000 die annually
  • 5-15 years old: age group with highest intensity
  • Children are vulnerable
  • Overall local prevalence
  • School-aged children: 27.7%
  • Preschool children: 30.9%
• Larval Forms

  • Microfilaria
  • Prelarval form of filarial worms
• Strongyloides stercoralis


  • Long esophagus, no terminal bulb
  • Usually, infective stage to the definitive host
• Biology: Adult

  • Anterior End: Mouth with three lips, and sensory papillae, Small triangular buccal cavity
  • Posterior End: Male - ventrally curved with two spicules, Female - tapered
• Socio-economic factors

  Affect the level of transmission of STH
• Biology: Adult

  • Habitat: Small intestine
  • Large whitish or pinkish worms
  • Male: 10-31 cm long
  • Female: 22-35 cm long
  • Polymyarian somatic muscle arrangement
• Biology: Adult

  • Reproductive Organ in the posterior two-thirds: Male - single, long, tortuous tubule, Female - paired reproductive organ
• Biology: Larva


  • Larval morphology is similar to the adult, Production of pepsin inhibitor 3 (PI-3): protects the worm from digestion and phosphorylcholine that suppresses lymphocyte proliferation