320 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



As a general rule, four molts occur in the devel- 

 opment of the parasitic and terrestrial free-living 

 nematodes thus far observed, but there has been 

 no formal study on the life cycle of any of the 

 marine nematodes. Neither has the embryology 

 of any marme nematode been worked out. We 

 have recently observed the first three cleavages of 

 Euchromadora vulgaris collected at Woods Hole, 

 Massachusetts. In this species the first two 

 cleavages appear to be equal, while the third 

 cleavage is quite unequal in the derivatives of one 

 of the first two blastomeres. The few published 

 illustrations of nemic embryos in aphasmideans 

 would appear to indicate differences from the 

 established pattern in the Phasmidea. This 

 should be an interesting field of investigation. 

 Most species produce relatively few eggs; 1 or 2 

 fully formed eggs per uterus is the rule in small 

 forms such as Monhystera and Chromadora, but 

 some of the larger forms such as Oncholaimus may 

 contain up to 20 mature eggs per uterus. The 

 number of eggs is characteristic of the species. 

 Eggs may be deposited in the one cell condition 

 or in various stages of development, and a few 

 viviparous marine nematodes have been reported. 



Saline content of the water in which the marine 

 nematodes live must be an important factor in 

 their life, since there is practically no overlapping 

 between marine and fresh-water inhabitants. 

 Attempts to acclimate marine nematodes to fresh 

 water, and vice versa, have been unsuccessful. 

 Rhabditis marina has recently been found on 

 decaying seaweed along the beach at Woods Hole, 

 Massachusetts. This form has been cultured with 

 bacteria on nutrient agar made up with either sea 

 water or tap water. Specimens taken from either 

 substrate may be transferred directly to tap water 

 or sea water. Both rhabditids and tylenchids are 

 usually soil or fresh-water inhabitants. Study of 

 their osmotic relations should prove interesting. 

 In the Nematoda, as in the Protozoa and Turbel- 

 laria, the excretory system is best developed in 

 fresh-water and soil groups (Phasmidea) and less 

 well developed in the marine groups (Aphasmidea). 

 A study of estuarine forms would probably be 

 very helpful in determining the conditions of 

 transition from a marine to a fresh-water biotope. 



On the other hand, the influence of oxygen 

 tension is probably not so important as has been 

 surmised. Chitwood and Chitwood (1938) con- 

 cluded that Chromadora quadralineoides and Oncho- 



laimium oxyure var. domesticum were highly 

 oxygen loving, since they were found in abundance 

 on an aquarium aerator. However, we have 

 cultured the former species for 2 months aad the 

 latter for an entire year in small unaerated aquaria. 

 Probably they are able to help satisfy their oxygen 

 requirements from the green algae on which they 

 feed. Few appear to be adapted to anaerobic life. 



LITERATURE CITED 



Allg£n, C. a. 



1947a. Papers from Dr. Th. Mortenson's Pacific 

 Expedition, 1914-1916, on some free-living marine 

 nematodes from Tobago (Br. W. I.). Vidensk. 

 Medd. Dansk. Naturl. Foren-Copenhagen 110: 45-63. 

 1947b. Idem. West American marine nematodes. Ibid. 

 110: 65-219. 

 Baylis, H. a. 



1915. Two new species of Monhystera (nematodes) 

 inhabiting the gill-chambers of land crabs. Ann. 

 & Mag. Nat. Hist., ser 8 (95), 16: 414-421, figs. 1-6. 

 Chitwood, B. G. 



1935. Nematodes parasitic in, and associated with 

 Crustacea, and descriptions of some new species and 

 a new variety. Proc. Helm. Soc. Washington 2 (2) : 

 93-96, fig. 22. 

 1951. North American marine nematodes. Texas Jour. 

 Sci. 3 (4): 617-672, figs. 1-15. 

 and Chitwood, M. B. 



1938. Notes on the "culture" of aquatic nematodes. 

 Jour. Washington Acad. Sci. 28 (10): 455-460. 



1950. An introduction to nematology. Sec. I. Anatomy, 

 213 pp. 



Cobb, N. A. 



1912. Further notes on Tricoma. Jour. Washington 



Acad. Sci. 2 (20): 480-484, figs. 1-2. 

 1920. One hundred new nemas. Contr. Sci. Nematol. 



(9): 217-343, figs. 1-1 18c. 

 1928. A new species of the nemic genus Syringolaimus 

 with a note on the fos.sorium of nemas. Jour. 

 Washington Acad. Sci. 18 (9): 249-253, figs. 1-3. 

 De Man, J. G. 



1892. Ueber eine neue, in Gallen einer Meersalge 

 lebende Art der Gattung Tylenchus Bast. Festschr. 

 70 Geburtst. R. Leuckarts, 121-125, 3 figs., pi. 16, 

 figs. 1-14. 

 Schneider, Wilhelm. 



1939. Wurmer oder Vermes II. Fadenwurmer oder 

 Nematoden. Die Tierwelt Deutschlands und der 

 angrenzenden Meeresteile. Jena. 270 pp. 



Stekhoven, J. H. S. 



1935. Nematoda Errantia. In: G. Grimpe and E. 

 Wagler (eds.), Die Tierwelt der Nord- und Ostsee, 

 Teil Vb, 173 pp. 

 TiMM, Richard W. 



1951. A note on the cell inclusions of Syringolaimus 

 smarigdus Cobb, 1928. Proc. Helm. Soc. Washington 

 18 (2): 125-126. 



