NEMATODES

                       

1)      Shape-  They are elongated , cylindrical or filiform in shape and unsegmented worms without any appendage .

2)      Size -  The size of a bnematode varies from 1 mm to 1 meter in length . The small size nematodes are

              ( I ) Strongyloides stercoralis – There are two forms –

a)       Parasitic form – Parasitic male is seldom seen . Parasitic female measures

                            2.2 mm by 0.075 to 0.3 mm .

b)      Free living form – The female ( rhabditiform ) measures 1 mm by 0.06 mm .

     

         (II)      Trichinella spiralis – The male measures 1.5 mm in diameter . The female   

                                         measures 3 to 4 mm in length and 0.06 mm in diameter .

The largest nematode is Dracunculus medinensis . The female worm which measures about 1 meter in length .

3)      Body surface – The body is covered with a tough resistant cuticle . Longitudinal muscle fibres are present .

4)      The body cavity – The body cavity is unlined pseudocele . Various organs lie in the body cavity . Digestive system an d genital systems float in the body cavity . Excretory and nervous systems are in rudimentary stage . They have no circulatory or respiratory organs .

5)      Sexes -  They are sexually differentiated . The male is generally smaller than  the female . The mouth end of both of the sexes are same but posterior end of the male is coiled ventrally where as in female it is straight .

6)      Alimentary canal -  The alimentary canal is complete . The alimentary canal consists of oral aperture , mouth cavity , oesophagus  , intestine and a subterminal anus . The mouth cavity may contain lip with teeth or cutting plate . The intestine is flat or cylindrical tub e and lined by a single layers of cells .

7)      Nervous system -  This consist of a dorsal , a ventral and four lateral longitudinal trunks with transverse commissures  . The nerves terminate in all organs .

8)      Sensory receptor -  There are some special receptor or sensory organs present in  the nematodes , namely amphids ( olfactory receptor ) , tactile papillae , deirids and phesmids ( caudal chemoretors)  .

9)       Reproductive system -  The nematodes of man are all diecious helminths means the sexes are separate .

(A)    The male genital system – It consist of a long convoluted tube differentiated  

                 into testis , vas deferens , seminal vesicle an d ejaculatory duct . It    

                 opens with the intestine into a common cloaca . Accessory  

                 copulatory organs like one or two unsheathed spicule and   

                 gubernaculums are present . In some cases , copulatory bursa may    

                 be present .

         ( B )  The female genital system – It consist of a single or double convoluted tube .

                                 This tube is differentiated into ovary . Oviduct seminal receptacle ,  

                                  uterus , vagina and valva . The female genital organ ends into   

                                  genital pore which opens on the vental surface of the worm either in

                                  the middle of the body or near the mouth . In case of double tubes ,

                                  the tubes unite form vagina and en ds in the genital pore . The

                                 female nematodes may be divided as –

(a)                 Oviparous          –   The female nematodes lay eggs

(b)                Ovo-viviparous  –   The female nematodes lay eggs which will contain larva

                                  which are immediately hatched out .

(c)                Viviparous          –   The female nematodes give birth larva and they have no       

                                   egg .