hiding in cracks among stones, near tree trunks or among shrubs. Like a 

 relict, the evolution of the adults of this family was retarded, so that we can 

 establish only 2 large primitive genera (Rhyacophila and Himalo- 

 psy che) in the recent fauna, among the adults of the Rhyacophilinae; 

 however, the diversity and morphological specialization of the larvae of 

 Rhyacophila developing under the dynamic life conditions of streams 

 are greater than the differences which in other groups became generic or 

 even subfamily characters, e. g., different shape and size, presence or absence 

 of gills, diversity of form of gills and anal legs and highly differentiated 

 158 primary chaetotaxy. There are highly specialized characters in the larvae 

 of Rhyacophilidae, on the background of its general primitive character 

 which resulted in the characters of the adults; this explains the recent 

 flourishing and wide geographical distribution of the family. The high 

 specialization of the larvae of some forms of the Palearctic Rhyacophilinae 

 is even more sharply and widely expressed in the Australian subfamily 

 Hydrobiosinae in the modification of the forelegs of the larvae into forceps 

 or other structures. 



In an article on phylogenetic relicts, Rohdendorf (1959) states the reason 

 which explains the survival of ancient organisms under recent life 

 conditions, i. e., the possession of certain useful specific characters; 

 Rohdendorf (ibid.:50) writes: "The appearance of a few one-sided adaptations 

 may prove so useful in the evolution of an ancient branch that it enables it 

 to develop into a progressive, widely distributed group." Such is the family 

 Rhyacophilidae, for example, the adults of which are nearly a phylogenetic 

 relict according to its morphology and mode of life, while the highly 

 specialized and progressively developed larvae have ensured the large 

 number of species and wide geographical distribution of the family. 



The primitive characters of organisms which do not correspond to the 

 concept of phylogenetic relicts are retained in the same manner, e. g., in 

 the highly progressive family Hydropsychidae. 



A discussion on the primitive or specialized appearance of a group should 

 be based on all characters of morphology, biology and its success; however, 

 isolated primitive morphological characters of a group may be present 

 throughout a system, in the different systematic categories. 



Such characters are present in the Annulipalpia, both in the lower 

 Rhyacophilidae and in the higher Hydropsychidae (and also to a greater or 

 lesser extent in all intermediate forms). This is true also of the Integri- 

 palpia. In other words, primitive characters retained by the larvae of 

 Trichoptera from ancestors are more or less characteristic for the lower 

 families which are isolatedly represented and distributed in all ranks of 

 the system. 



We attempt to give below an at least one-sided representation of the 

 main lines of the phylogeny of the order in the light of new data on the 

 morphology and biology of the larvae, including the data in the systematic 

 chapter. 



To clarify this problem on the basis of the diversity of the characters of 

 the various families, we shall attempt to define the phylogenetically 

 important characters. We shall limit ourselves to the larvae of Annuli- 

 palpia as they are a more ancient and primitive suborder with clearer 

 phylogenetic relationships among its families. The phylogenetic relation- 

 ships among the families of Integripalpia are more complex and not 

 sufficiently clear. 



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