head and relatively long abdominal setae, a small dorsal sclerite of the 

 9th abdominal segment, slightly elongate and simple anal legs resembling 

 those of the lst-stage larvae; the group also includes some lower Rhya- 

 cophila which, unlike all the other forms of the group, are not predators 

 but phytophages (R h, laevis Botosaneanu, 1956c:590— 594), which do not 

 build a pupal cavelike shelter (they are closely related to the Hydroptilidae). 



The larvae of a part of the Rhyacophilidae is highly differentiated, but 

 has not lost the primitive characters present in the whole family. The 

 larvae of some groups lost the teeth of the mandibles; the abdominal 

 segments are flattened, the integument relatively hard, and there are gills 

 1°1 of a varying degree of complexity; the 9th abdominal segment is markedly 

 sclerotized; the anal legs are more complex and their sclerites bear 

 crotchets and processes; the form of the claw is different; a more or less 

 complex sculpture is present on the sclerites in some forms. In the higher 

 forms, the primary chaetotaxy is markedly differentiated; it is specialized or 

 reduced in some places; some setae on the legs and anal legs are trans- 

 formed into spines and are sometimes movable. In spite of the complex 

 structure of the higher Rhyacophilinae, the characteristic appearance of 

 the larvae is retained in the whole order; the family can be identified even 

 in the most highly specialized forms. The subfamily Hydrobiosinae, which 

 is represented in the USSR by 1 genus and 2 species, shows a remarkably 

 high specialization of the forelegs (see p. 321 ) but its abdomen shows the 

 small size and cylindrical form characteristic of the lower forms. 



The high specialization of the larvae of some species developed during 

 adaptation to life under the diverse conditions in the highly dynamic 

 environment of streams, including large turbulent mountain brooks and 

 rivulets. 



Thus, in spite of the high specialization of the larvae of some groups, 

 the position of the Rhyacophilidae at the beginning of the sequence of 

 families of the order may be considered well established. 



The complex differentiation of the species inside a genus induced some 

 authors to divide it into groups of species according to the structure of the 

 larvae or according to the male genitalia (Dohler, 1950; Ross, 1956:75—126).* 



The larvae of Glossosomatidae are more specialized, and differ markedly 

 from those of Rhyacophilidae; the close relationship between these 

 2 families is most clearly marked in the pupae, which build a thick cocoon 

 resembling that of Rhyacophila; this cocoon is enclosed in a similar 

 cavelike pupal shelter. Unlike the larvae of Rhyacophilidae, the larvae of 

 Glossosomatidae build a shieldlike portable case in the first stage, which 

 (unlike the pupal case) has a ventral wall. The larvae show little 

 resemblance to the larva of Rhyacophila; the head is prognathous but 

 inclined downward (pseudohypognathism) because of the enlarged pronotum; 

 the setae of the posterior part of the head's dorsal surface, which is covered 

 with a process of the anterior margin of the pronotum, are displaced 

 anteriorly and are grouped behind the eyes; several of these setae are 

 markedly reduced. The secondary chaetotaxy of the pronotum (in some 

 genera also of the mesonotum) is relatively rich; mesonotum and metanotum 

 sometimes bear small dorsal sclerites. The abdominal segments are 

 cylindrical and bear small setae. The dorsal sclerite of segment 9 is well 



See pp. 132, 133. 



151 



