with running water; the species of Phryganea and Agrypnia inhabit 

 not only lacustrine plant thickets but also riverine thickets in the plains. 

 These species are often more abundant in the estuaries of these rivers than 

 in lacustrine plant thickets, because of the more favorable oxygen regime; 

 114 genera living only in small sphagnum marshes (Holostomis, Oligosto- 

 mis, Neuronia, Hagenella) develop well also in drainage canals with 

 a slow current and dark water. 



WATER BODIES AND BIOTOPES INHABITED 

 BY CADDIS FLIES 



Of the large diversity of water bodies inhabited by Trichoptera, we 

 mention only the few types in which the Trichoptera are represented 

 regionally. 



Water bodies of similar types (springs, brooks, rivulets and rivers with 

 a similar hydrological regime, lakes of the same type with a similar bottom) 

 are inhabited in different regions by different groups of species; these 

 different groups which are restricted to water bodies and biotopes of similar 

 type have the same ecological characteristics and are isoecological. 



The present chapter discusses such isoecological groups which inhabit 

 running and stagnant water bodies in different regions in the USSR.* 



Springs 



The division of springs into limnocren, rheocren and heleocren springs 

 does not always correspond to the emergence of underground water. In 

 large regions of springs in which only a fauna characteristic for this region 

 could develop, there is usually an intricate network of various types of 

 water bodies (usually micro-water bodies) with an underground supply which 

 is often connected. The stream of underground water (a trickling source or 

 small brook), depends on the relief of the locality, and is either a small brook 

 (rheocren, i.e., running spring) or an accumulation of water in depressions, 

 forming a more or less closed and slowly flowing water body or micro -water 

 body (limnocren, i.e., stagnant spring); when the relief is flat or slopes slightly, 

 the ground water is retained in the soil or flows over stones, forming small flows 

 overgrown with moss and other plants (heleocren, i.e., marshy spring).** 



A constant low water temperature (4—6°) is maintained near the 

 emergence of underground water throughout the year, preventing the freezing 

 of the source in winter; the further away from the point of emergence, the 

 more marked are the daily and seasonal fluctuations of the water 

 115 temperature; in localities with shallow floods supplied by springs, the water 

 temperature sometimes rises to 16—18° and more in summer. Areas 



* However, there are very few stenotopic species, i.e., species restricted to one biotope; they are much less 



numerous than species with a broader ecological range. There are no "eurybionts" among Trichoptera. 



"" It is not justified, as proposed by V.I. Zhadin (1950b :708), to place a narrow terminological meaning to the 



popular names of sources such as "rodnik" and "klyuch, " which are used widely and inaccurately in the 



geographical and hydrobiological literature. 



105 



