J'iorpholo;'y A, V.-.l 



NlT^lATODE MORPHOLOGY 



General Structiire of a Nematode 



Nematodes are triploblastic, bilaterally symmetric, unsegmented, non- 

 coelomate animals. Their shape is more or less cylindrical, sometimes 

 fusiform, pear-shaped or otherwise modified, particularly in the adult 

 female. The mouth opening is generally anterior and is usually sur- 

 rounded by lips bearing sensory organs. The mouth is followed by a 

 mouth cavity or stoma, an esophagus, intestine, and a rectum terminating 

 in a ventral terminal or subterminal anus in females, or a cloacal 

 opening in males. The body is covered with cuticle. There are usually 

 no external appendages, but appendages do occur in rare forms. The 

 body wall is composed of a hypodermis or epithelium which is situated 

 beneath the cuticle, ^nd a single layer of muscles. Sexes are usually 

 separate. The male reproductive system opens directly into the rectum 

 forming a cloaca, while the reproductive system of the female has a 

 separate opening, the ventrally situated vulva. Excretory and nervous 

 systems are present, but there are no specialized organs of circulation 

 or respiration. 



External Characters 



The nonatodes, or roundworms, are generally vermiform animals of long 

 cylindrical shape, circular in cross section. There are two general 

 types of body form, the fusiform and the filiform , the latter being 

 less common. The fusiform is that of an elongated spindle, widest 

 through the middle and tapering toward the blunt or pointed ends; the 

 posterior end is generally more tapering and pointed than the anterior 

 end and in some species is very slender. Filiform is thread-like with 

 a uniform body diameter throughout. Other variations are the short, 

 plump, pyriforrii or oval shape assumed by females of Heterodera and 

 Meloidogyne . Most attain a length of 3 to U mm. Males are nearly always 

 smaller than the females (Plate I). 



Nematodes in general lack coloration, being transparent or of a whitish 

 or yellowish tint conferred on them by the cuticle. 



The body is not divisible into definite regions and lacks a distinct 

 head, although this term is sometimes applied to the anterior end. The 

 ventral surface of nematodes is identifiable by the presence in the 

 mid-ventral line of the e xcretory pore (Plate I, Fig. 1, G), the gono- 

 pore in the female, and the anus. In most forms, the excretory pore 

 is located about opposite the base of the esophagus. The vulva (Plate 

 I, Fig. 1, Q) is usually situated in the oosterior body half. The anus 

 or cloacal opening of the malQ (Plate I, Fig. 1 and 2, U) lies near the 

 posterior end. The body region behind the anus is commonly called the 

 tail. 



The oral opening is surrounded by six lips (Plate I, Fig. 3, B) in 



