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.

Brief History

 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.

Important Characters

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.