PHYLUM NEMATODA (= NEMATHELMINTHES )
Definition and Introduction
Bilateral and protostomial organ grade eumetazoans in which the space between body wall and alimentary canal is a false body cavity ,or pseudocoel , derived , from embryonic blastocoels. The term Nematoda literally means threadworms or roundworms (Gr. Nema = thread + eidos = form )About 12,000 species known.
Ancient people were familiar with certain large sized nematode parasite of domestic animals . Minute nematodes were discovered only after the invention of microscope. Linnaeus (1758) included these in vermes Rudophi (1793,1819) included these under Nematoidea Gegenbaur (1859 ) ultimately proposed Nema thelminthes for these.
1. Many endoparasited of various animals and plants other free living and widely distributed in all sorts of water and damp soil.
2. Mostly minute or small , some large ( 1mm to 25 cm) some upto several metres long.
3. Slender , cylindrical , elongated body usually tapering towards both ends, unsegmented .
4. Body wall formed of a thick , tough and shiny cuticle, a syncytial hypodermis beneath cuticle. And innermost layer of peculiar ,large and longitudinally extended and muscle cells arranged in four quadrants .
5. The false body cavity or pseudocoel is spacious with a fluid but no free cells
6. Straight alimentary tract with terminal mouth and anus.
7. Circulatory system and respiratory organs absent. A simple excretory system , comp aratively simpler or complicated sensory organs and well developed nervous system, present .
Reproductive system well developed. Usually unisexual with sexual dimorphism,Many kinds of nematodes are arasites of useful plant and domestic animals . Some of these are pathogenic to their hosts, causing serious diseased. Even man is a host for more than 50 species . of which ascaris lumbricoides . and Enterobius vermicularis are very common ,Other human nematodes are wuchereria which causes filarial , Trichinella causing trichinosis ,and ancylostoma causing hookworm disease.