Number and arrangement of gills ofN. c i li ar i s (after Siltala) 



Segment 



Dorsal 



Pleural 



Ventral 



2 



3-4 



2-5 



4-5 



3 



4-5 



3-4 



4-5 



4 



2-5 



1-2 



3-5 



5 



i-4 



1 



3-5 



6 



1-3 



1 



3-5 



1 



1 (0) 



1 (0) 



2-5 



8 







2-4 



Mode of life and habitats. Phytophagous, in brooks and rivulets 

 with a rapid current. 



Distribution. Northern, central, and western parts of the European 

 USSP; Caucasus. In addition. Central and Northern Europe. 



2. Genus Sericostoma Latreille 



539 



Full-grown larva. Length 11.0— 16.5 mm. Head brownish dorsally. with 

 light dots, light ventrally; gula wide, cup -shaped, rounded posteriorly, fused 

 v/ith large, lateral sclerites; gular suture absent. Mesonotum thin, light, 

 very weakly sclerotized, divided in each half, with a thin, curved suture 

 separating a narrow, long, lateral area. Metanotum membranous, with a 

 small sclerotized dot in anterior part. Gills with 2—4 filaments, or single 

 and small. Case 15— 18 mm long, made of sand grains, smooth, slightly 

 curved, slightly tapering posteriorly. 



The larva passes 6—7 stages. 



Pupa. Length 1 1 .0—14.2 min. Wing sheaths reaching middle or posterior 

 margin of segment 7; segments 1—4 of mid-tarsi with thin, grayish, 

 natatorial setae; sparse setae on segments 1—4 of fore tarsi. Gills with 

 2—4 filaments, some of them single. 



Case 12 — 16 mm long, usually lying on bottom, sometimes, if current is 

 strong, attached to stones at posterior end; anterior end laterally with 

 large sand grains or small stones; posterior end with domelike, convex 

 membrane with a single slitlike hole. 



Mode of life and habitats. Detritophagous, in springs and brooks, 

 in shallow areas of calm water near the bank; sometimes among humid 

 vegetation in oozing springs. 



Distribution. Northern and western parts of the European USSR, 

 Caucasus. In addition Europe, southwest Asia. 



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