THE SCREW NEMAS 



(Ascarophis van Beneden, 1871) 



PARASITES OF CODFISH, HADDOCK AND OTHER FISHES 



CONTRIBUTIONS TO A SCIENCE OF NEMATOLOGY XVII 



BY N. A. COBB 



The screw-nemas, as it is here proposed to call them, have yet to be 

 adequately studied. Not very much has been added to van Beneden's 



original description. Almost nothing 

 is known about their life history and 

 habits. However, the present commun- 

 ication adds considerably to our knowl- 

 edge of their morphology. The sug- 

 gested explanation of the remarkable 

 screw form, and its probable mode of 

 evolution, present the nemic cuticle in 

 a new role. (See Figs. 5, 6, and 7.) 



Considering the number of screw- 

 nemas thus far seen, it is remarkable 

 that no males have been discovered. 

 Nicoll records screw-nemas as "ex- 

 tremely numerous" in haddock. Van 

 Beneden found them originally in the 

 codfish; Nicoll, in the codfish and had- 

 dock, and in the fishes Hippoglossus 

 vulgaris and Coins bubalis; MacCallum 

 now finds a species in the stingray. 



Nemas so widespread and numerous 

 probably have economic significance. 

 This probability can not be dismissed 

 by citing the absence of definite evi- 

 dence to the contrary, for, at rather 

 frequent intervals nowadays, nematolo- 

 gists are showing that nemas long 

 known and lightly regarded, are not 

 only of some importance in their rela- 

 tionship to mankind but sometimes of 

 great importance; and the multitudi- 



X400 



Fig. 1. Head and tail end of 

 Ascarophis helix n. sp. Above, to 

 the right, front view of the lip 

 region. The head end is nearly a 

 ventral view, but slightly oblique. 

 The tail end is a dorsal view, and 

 the anus, being on the far side, is 

 but indistinctly shown. 



nous ways in which this comes about may well give pause to any who, 



Waverly Press, Baltimore, Md., June 9, 

 out material alterations. 



From Jour. Wash. Acad. Sc., Feb. 19, 1928. Repaged with- 



