Lecture 10 - Nematoda

• Many protostomes possess a cuticle.

  *Non-living outer layer secreted by epidermis.
• Cuticle restricts growth and must be molted via ecdysis.
• Regulation of molting achieved by the hormone ecdysone.
• Members of Ecdysozoa molt cuticle as they grow.
• About 25,000 species of nematodes are described, but as many as half a million may exist.

  • Many prefer the name Nemata for this phylum.
• Caenorhabditis elegans is an important model for studies of genomics and cell development and differentiation.
• Triploblastic – three embryonic germ layers. 
• Pseudocoel – used as hydrostatic skeleton.
• The cylindrical bodies of nematodes are covered by a tough coat called a cuticle.
• • Nematodes molt 4 times.
  • The old cuticle separates from the epidermis and the innermost layer is partially hydrolyzed
• A new cuticula is secreted by the hypodermis starting with the epicuticle
• Ring of nerve tissue and ganglia around the pharynx lead to dorsal and ventral nerve cord.
• Sensory papillae at head and tail.
• Amphids, pair of sensory organs on head, lead into a deep cuticular pit with modified cilia.
• Reproduction in Males

  • The female is held by the male within the bursa
  • The male inserts copulatory spicules
• • The sperm duct is muscular an sperm is transferred to the female against the pseudcoel pressure
  • Male cement glands can close vulva in some species
• Reproduction in Females

  • Most female nematodes have two ovaries
  • Structure is similar to the linear male system, oogonia are produced at the distal end and mature into oocytes while they move into the growth zone
• As the oocytes enter the oviduct

  they are fertilized by sperm stored in the receptacle
• Parasitic nematodes of humans:

  • Intestinal roundworm (Ascaris)
  • Hookworm
  • Pinworm
  • Trichina worm
  • Whipworm
• Nematode Diversity

  • Class Aphasmidia (Adenophorea)
  • Class Phasmidia (Secernentia)
• Trichuris trichiura (whipworm)

  • The third most common round worm of humans. Worldwide, with infections more frequent in areas with tropical weather and poor sanitation practices, and among children (800 million infected).
• Trichuriasis occurs in the Southern United States (locally up to 20%, detected in 1.2% stool samples across U.S.
• Adults live in cecum where the female worm produces 20,000 eggs per day which are shed with the feces.
• Embryonation occurs within 3 weeks in soil.
• Trichinosis is caused by infection with Trichinella spiralis.
• The larva is freed from its nurse cell, and enters the mucosa of the small intestine.
• The females give birth to live larvae while tunneling the epithelium.
• The larvae enters a muscle cell and lives as an intracellular parasite developing in the cytoplasm of the host cell.
• • The end product is a nurse cell
  • A fine net of blood vessels forms around the nurse cell(angiogenesis)
• The host cell looses its myofilaments and several additional subcellular changes occur.
• Both host cell and worm are enclosed by a collagen capsule (collagen mRNA has been detected in nurse cell, but some authors suggest the capsule is secreted by surrounding fibroblasts)
• Enterobius vermicularis

  • they are tiny
  • 2-13 millimeters
  • ivory or pearly-white in color
  • have separate sexes
  • life span: 2 mos.
• Enterobius vermicularis

  female:

  • 8-13 mm
  • 0.3 - 0.5 mm in diameter
  • pointed tail
  • has 2 uteri, vagina, & ovaries
• Enterobius vermicularis

  male:

  • 2-5 mm
  • 0.1 – 0.2 mm in diameter
  • curved tail
  • testicle, vas deferens, seminal vesicle, & ejaculatory duct
• Ancylostoma (Hookworms)

  • Small nematodes (1-1.5 cm)
  • Head is slightly bend (hook) and the ‘mouth carries characteristic teeth (Ancylostoma) or plates (Necator, note that these are not real teeth but cuticular formations of the ‘buccal capsule)
• The posterior end of the male worm is elaborated into a copulatory bursa
• Turbatrix aceti

  • known for feeding on the acidic bacteria
  • location is the thin meniscus at the edge of the liquid
  • wide range of temperature from 60 to 90 degrees
• Ascaris

  • Large intestinal nematodes (Ascaris lumbricoides infects humans, A. suum infects pigs, the species are almost indistinguishable, but have clear host specificity)
• Eggs are sensitive to sun light but otherwise extraordinarily resistant (ascarosides - special glycolipids secreted by the embryo)