gliding, crawling when assisted by body bristles or 

 other devices, and in microsoopic worms a kind of 

 thrashing about, which in open water leads nowhere. 

 Among aquatic plant debris, in sand or mud, in soil, 

 or in the fluids or tissues of a host, friction against 

 solid particles may help the whiplike contortions to 

 move minute worms along or enable them to explore 

 their surroundings. 



Marine nematodes are on the whole the largest of 

 the free-living forms; some are nearly 2 inches long. 

 They turn up in any sample of shore sand or mud, 

 but especially in soft muds full of the microscopic 

 plants and organic debris on which they feed. On 

 such bottoms they are the most numerous of all mul- 

 ticellular animals. A handful of muck could easily 

 contain many thousands of individuals of fifty or 

 more species. Even in antarctic waters a thimbleful 

 of bottom material will teem with hundreds of nema- 

 todes of species common almost anywhere. The rec- 

 ord depth for bottom-living nematodes is more than 

 21,000 feet. 



Fresh-water forms are also widely distributed, 

 being carried about by currents, by wading birds and 

 other animals, or by drifting plants. They occur in 

 still or running water, but are most abundant on the 

 shores of lakes, where they favor stony or muddy or 

 plant-invaded bottoms. Some have hollow stylets and 

 suck plant juices; others are feeders on decaying par- 

 ticles; many are voracious feeders on protozoans, on 

 other nematodes, or on their little relatives, the 

 rotifers and gastrotrichs, discussed later in this chap- 

 ter. Nematodes able to survive in hot and sulphur 

 springs in Germany are of the same or closely related 

 genera as those found in Yellowstone Park in the 

 United States or in hot springs in China. Those of 

 swift or tumbling mountain streams are able to fas- 

 ten by sticky secretions from glands at the tail tip, 

 and such adhesive glands occur in most free-living 

 nematodes, though not in the parasitic ones. 



Land nematodes are spread about by winds and 

 plants and other animals, almost like protozoans, and 

 indeed they are similarly suited for wide dispersal of 

 the same common species by their small size and 

 habit of resisting drying when in an inert state. Some 

 species, however, have very specific niches, and the 

 one most often pointed out is Tiirhatri.x sihtsiae. de- 

 scribed from the felt mats on which beer-drinkers set 

 their mugs in Silesia, in Germany. A relative, Tiirba- 

 trix ciceti. long called the vinegar eel, feeds on the or- 

 ganisms that form the "mother" of naturally ferment- 

 ing vinegar. 



The mermithid nematodes, such as Menriis above, 

 are long, threadlike worms that taper less than 

 typical members and are often mistaken for the hair- 

 worms described later in this chapter. They do, how- 

 ever, taper more than the hairworms. The adults are 

 from a few to 20 inches long, and are found in soil, 



sometimes in water, but do not feed. The juvenile 

 stages are parasitic in insects, often in grasshoppers 

 or crickets, feeding on all the organs as they grow to 

 adult worms and then emerge. Mermithid damage to 

 insects should be of some consolation to farmers, be- 

 set as they are with nematodes harmful to crops. 



The free-living soil nematodes have been carefully 

 estimated in Danish soils, where grassland may 

 teem with almost 2,000,000 worms per square foot, 

 and cultivated soils with up to 200,000 worms in the 

 same area. For most species 90 per cent of them can 



Mermis, a mermithid nematode worm. (Pennsylvania. 

 Ralph Buchsbaum) 



be found in the top two inches of soil, and none be- 

 low four inches. Some soil nematodes have been re- 

 ported, however, down to a depth of twenty-five feet. 

 The smaller ones, perhaps only ';,,, of an inch in 

 length, feed on bacteria and small algae. The larger 

 ones with teeth or grinding devices feed on proto- 

 zoans, rotifers, and other nematodes. To gather 

 them for microscopic examination one needs to put 

 fresh garden soil in a piece of cheesecloth and set it 

 in a funnel stopped by rubber tubing and a clamp. 

 When the funnel is filled with water, the nematodes 

 wriggle downward into the stem and collect there. 

 After some hours the water in the stem can be run 

 into a glass dish. 



[135 



