ParaH. H:l 



RINQ NEMATODES (CRICONEMOIDES SPP.) 



Rinf); nematodes are fairly common in agricultural soils and sometimes 

 occur in great numbers. However, because of their rather odd shape and 

 slup;gish movements, they may sometimes be overlooked. Shape is typi- 

 cally plump, since they are usually only about ten to fifteen times as 

 long as wide. Often the body is strongly curved, as shown in Fig. 7^ 

 of Goodey's "Soil and Freshwater Nematodes." Once found, identification 

 to genus presents no special difficulty. The cuticle is strongly annu- 

 lated, and the annules are retrorse (directed backward). Apparently 

 this feature is connected with their locomotion, which is of a somewhat 

 different type than the serpentine motion of longer and slimmer nematodes. 

 Ring nematodes move through the soil by alternate contraction and expan- 

 sion of the body, the retrorse annules acting somewhat in the fashion of 

 a ratchet, catching on soil particles when the body is extended, and 

 slipping past when the body is contracted. The common rame, "ring nema- 

 todes," is applied to two genera, Criconema and Criconemoides . These 

 are closely related, differing mostly in that the annules of the latter 

 are smooth, while those of the former are fringed with scale-like pro- 

 jections, the shape and arrangement of which varies with species (Fig. 76, 

 Goodey) . Criconema appears to be rare in agricultural soils, but is 

 often found in forest soils. 



Ring nematodes are usually about one-half millimeter long. Tliey have 

 stylets which are often-one-tenth of the body length and may be as long 

 as one-third of the body length. The stylet knobs are well developed 

 and are to be seen in the anterior part of the median oesophageal bulb 

 when the stylet is retracted. 



An aid to identification to species is "On the Morphology of Criconeraoidesj 

 etc.," by Dewey J. Raski (Proc. Helmin. Soc . Wash. 19(2): 8^-99 of 1952). 

 This paper has a key to the species and is copied for inclusion in these 

 Notes. 



Very little information, either on the biology or pathogenicity of ring 

 nematodes, is available. It is quite certain that they are plant-para- 

 sites. Steiner (Plant Nematodes the Grower Should Know) presents a 

 photograph of a ring nematode partially embedded in a root, though it 

 .is probable that most feeding is done from the outside of the root. It 

 is a fair assumption that this feeding kills or injures cells and that 

 the dead tissue might provide an entrance for pathogenic bacteria or 

 fungi which could not otherwise attack the plant. 



Present evidence that ring nematodes may be a cause of important losses 

 in crops is mostly limited to observations of great numbers of ring 

 nematodes associated with roots of plants which were growing poorly. 



