- The phylum ‘Nemathelminthes’ (Gr; nematos = thread ; helminths = worm) or Nematoda comprises the roundworms.
- Triploblastic, bilaterally symmetrical, vermiform, unsegmented cylindrical true worms with pseudocoel (i.e pseudocoelomate or blastocoelomate)
- Pseudocoelom / False coelom derived from embryonic blastocoel.
- Tube within a tube body plan, organ-system grade of body organization.
- Body round in cross section and covered with transparent cuticle composed of scleroprotein.
- A syncytial epidermis generally without cilia.
- Body wall has only longitudinal muscles.
- No distinct head, digestive tract complete usually surrounded by lips bearing sense organs.
- Alimentary canal of roundworms have both mouth and anus.
- Both respiratory and circulatory system are absent.
- Excretory system comprised of one or two renette cells or protonephridia.
- Nervous system consists of circumpharyngeal nerve ring and six longitudinal nerve cords.
- Presence of sensory papillae. (Amphids : in mouth, Phasmids : in anus)
- All are dioecious ; i.e. sexes are separate with sexual dimorphism. [1st unisexual phylum]
- Eggs with chitinous shell, cleavage determinate and spiral.
- Larval forms are : Rhabditiform, Filariform, Microfilariae etc.
- Classification : 5 classes [Rotifera, Gastrotricha, Kinorhyncha, Nematomorpha and Nematoda]
Examples:
- Ascaris lumbricoides (Round worm)
- Wuchheria bancrofti (Filarial worm)
- Enterobius vermicularis (pin / thread / seat worm / churna)
- Necator americana (Hook worm)
- Trichinella spiralis (Trichina worm)
- Loa loa (eye worm)
- Dracunculus medinensis (Guinea worm)
