Siltala (1907:598—599-) lists the primitive characters of caddis fly larvae. 

 Without committing himself decisively, he mentions, among other primitive 

 characters, the sclerotization of the dorsum in the form of small oval 

 sclerites on the abdominal and thoracic segments (like those of the larvae of 

 St a c t o b i a, family Hydroptilidae). Siltala's assumption is probably correct; 

 his view on the primary dorsal sclerotization of the larvae segments is 

 supported by the relationships presently existing in the ontogenesis of the 

 159 genus Agraylea: the lst-stage, 2nd- stage and 3rd-stage larvae of this 



genus (like the larvae of Stactobia) have dorsal sclerites on all abdominal 

 segments, which later (in the 4th and 5th stage) disappear on segments 1 — 8. 

 Nielsen listed a morphological analysis of the European species of 

 Hydroptilidae. He found not only in Agraylea, but also in Hydroptila, 

 Oxyethira and Orthotrichia, small tergites on the abdominal 

 segments of the larvae; he writes about the abdominal tergites of 

 Hydroptilidae: "These tergites must be regarded as a primitive feature" 

 (Nielsen, 1948:190). Ross observed dorsal abdominal tergites as clearly 

 marked as in Stactobia also in the larvae of Leucotrichia pictipes 

 (Ross, 1944:120, Figure 449); Ulmer found such tergites in the larvae of 

 Plethus cruciatus and Lamonganotrichia crassa ( Ulmer, 

 1957:192-196, 200-203; Plates 14-15, Figures 94 and 114). 



We are inclined to think that the presence of a tergite on the 9th 

 abdominal segment retained in the larvae of the 3 lowest families of Annuli- 

 palpia (Rhyacophilidae, Glossosomatidae and Hydroptilidae) and to a small 

 extent in the Hydropsychidae, and, in connection with case -bearing, is a 

 primary phenomenon in most genera of Integripalpia, while the loss of this 

 tergite is secondary. 



The sclerotization of the meso- and metanotum should probably also be 

 considered as primary, while the lack of sclerotization of the nota of these 

 segments and of the dorsum of the abdominal segments should be considered 

 secondary, developing with the increase of mobility of the larvae (which is 

 determined by its mode of life). In the Annulipalpia, the lack of sclero- 

 tization of the larva is most completely developed in the active predators 

 in the Polycentropodidae and in the higher Paleochaetoidea; the latter are 

 tube-dwelling microphages which continuously move inside the tube, 

 collecting microscopic food from the tube walls. The same also applies 

 to the predators of the family Polycentropodidae, which move and build 

 rapidly; they continuously renew their nets and actively prey upon the 

 organisms caught in them. 



The sclerotization of the meso- and metanotum of the larvae of the 

 3 other families of Neochaetoidea (Ecnomidae, Arctopsychidae and 

 Hydropsychidae) is an atavism; in the Ecnomidae, the previously mentioned 

 sclerites are thin and weakly sclerotized; in the Arctopsychidae, they are 

 partly divided by a transverse suture which increases mobility. In the 

 larvae of Hydropsychidae, the sclerotization of the meso- and metanotum 

 is probably connected with life in their narrow dwelling chamber. 



Among the tube -bearing Integripalpia, only the very mobile larvae of 

 Phryganeidae, which live in broad, straight tubes open at both ends, lost the 

 sclerites of the meso- and metanotum. Some genera however (Holosto- 

 m i s) retain rudimentary sclerites; in Yphria c a 1 if o r n i c a, these 

 sclerites are not rudimentary but are already a small plate; in the more 



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