FREE-LIVING NEMATODES OF THE GULF OF MEXICO 



By B. G. Chitwood and R. W. TiMM, formerly, The Catholic University of America 



NEMATODE ANATOMY 



Nematodes are unsegmented, triploblastic 

 pseudocoelomate, dioecious organisms witli a 

 complete digestive tract. Externally they are 

 invested with a noncellnlar cuticle composed of 

 various scleroproteins ; cilia are always absent 

 both externally and internally. Immediately 

 beneath the cuticle there is a cellular or syncytial 

 hypodermis concentrated in dorsal, ventral, and 

 paired lateral chords or ridges which project into 

 the body cavity. The musculature of the body 

 wall consists of a single layer of spindle-shaped, 

 iminucleate muscle cells attached throughout 

 their length to the hypodermis between the chords. 

 Since the dorsal and ventral musculature of the 

 body each acts as a unit, movement is whip-like or 

 eel-like. Because of the absence of circular or 

 diagonal muscle layers the squirming movements 

 and transverse contractions seen in turbellarians 

 and annelids are lacking in nematodes. The body 

 cavity is a pseudocoelom containing scattered 

 fixed cells of mesenchymatous origin. 



The oral opening is surrounded by lips and 

 sensory papillae or setae. Paired lateral cephalic 

 sensory organs, the amphids, are situated at the 

 labial or post-labial region; they are varied in 

 shape in the different groups of marine nematodes. 

 The mouth cavity or stoma is highly diversified 

 and often there is a relation of stomatal structure 

 to feeding habits. The esophagus is an elongate 

 muscular organ lined with cuticle; it contaias 

 three or five esophageal glands the orifices of 

 which may open into the lumen or through teeth 

 into the mouth cavity. Grossly the esophagus 

 may be cylindroid or may consist of several 

 distinct regions and be terminated by a bulb with, 

 or without, a valve. The intestine is a straight 

 tube consisting of a single layer of cells numbering 

 2 to perhaps 200 in circumference. Various types 

 of intestinal cell inclusions give characteristic 



appearances to the genera or species. These may 

 be organic or inorganic waste products, stored 

 food materials such as glycogen, oils, and pro- 

 teins, or absorption products such as plant 

 pigments. Finally, the digestive tract ends in a 

 rectum or cloaca lined with cuticle and opening 

 on the ventral side of the body but never 

 terminally. 



The reproductive system consists of one or two 

 tubular gonads. In the female the vulva is 

 ventral, usually near the middle of the body. If 

 paired, the ovaries are opposed and may be either 

 reflexed or outstretched. Most nematodes are 

 oviparous, but viviparous species occur in many 

 families. In the male the testes, if paired, are 

 usually opposed as in the female, but a common 

 duct, the vas deferens, extends from both gonads 

 posteriad to connect with the intestine and form 

 a common cloaca opening ventrally. Specialized 

 copulatory organs in the form of sclerotized 

 spicules are present in the male. A sclerotized 

 guiding piece, the gubernaculum, is almost always 

 present. In addition, the male generally has 

 copulatory sense organs varying according to the 

 different groups. 



Various glands empty externally through the 

 cuticle. Of these, the excretory system is the 

 most diversified. In the class Aphasmidea this 

 system consists of a single ventral gland cell in the 

 body cavity emptying through a duct which is 

 usually protoplasmic rather than sclerotized. 

 This is the condition in most aquatic nematodes. 

 In the class Phasmidea the excretory system has a 

 sclerotized terminal duct and one or two lateral 

 canals situated in the lateral chords. Unicellular 

 glands are also connected with the amphids and 

 with similar paired lateral caudal sensory organs, 

 the phasmids. Sublateral paired series of hypo- 

 dermal glands and three caudal adhesive glands, 

 emptying terminally at the tail, are also usually 

 present in the Aphasmidea. 



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