Nematoda

Nematoda

Diversity and Classification:

  • About 30,000 species have been observed, but it is estimated there are more than million 

  • 2 main classes:

    • Chromadorea

    • Enoplea


Biology and Importance

  • Commonly called Roundworms 

  • Huge diversity as they are found almost everywhere 

  • Both free-living and parasitic forms

  • Parasitic forms can affect humans, animals, or plants

  • Size ranges from less than a millimeter to meters

  • Caenorhabditis elegans  is the model organism

    • Used for studying

      • Development

      • Gene function

      • Programmed cell death


Form and Function (General Characteristics)

  • Triploblastic 

  • Unsegmented

  • Bilateral symmetry

  • Pseudocoelom

  • Cuticle covering body with various striations

  • Lack cilia and flagella

  • Muscle cells under epidermis, only run in longitudinal direction

  • Hypodermis thickened into chords, thicker laterally than dorso-ventrally


Nutrition and Digestion

  • Have a complete digestive system

    • Mouth, tube with specialized middle parts, and anus

  • Muscles surrounding the tube contract, squeezing the food and pushing it along in a process called peristalsis. Indigestible wastes pass out through the anus

  • Order of digestion

    • Mouth (swallows) -> pharynx (crushes) -> esophagus (moves) -> gizzard (grinds)  -> stomach (digests) -> intestine (absorbs) -> anus (eliminates)

  • Review picture for the different mouths


Excretion 

  • Excretes nitrogenous waste as ammonia via diffusion

  • Marine nematodes use renette glands to regulate water and salt balance; located under pharynx


Nervous system 

  • Simple nervous system consisting of a ring of nervous tissue that surrounds the pharynx

  • dorsal /ventral nerve cords run the length of the body


Reproduction

  • Most are diecious some are monoecious 

  • Male may by monorochi or diorchic

  • Males have spicule to assist with depositing sperm

  • Sperm lack flagellae and move by pseudopodia, like amoebas

  • Female may be monovarial or diovarial 


Class Enoplea

  • Characteristics

    • amphids pocket like, not spiral, usually post-labial. 

    • cuticle smooth or finely striated. 

    • phasmids present or absent.

    • esophagus cylindrical or bottle-shaped with 3 to 5 esophageal glands, stichosome or trophosome may be present.

    • simple non-tubular excretory system, usually a single cell.

    • female generally with two ovaries. 

    • male generally with two testes.

    • caudal alae rare