A comparative morphological study of lateral line systems in larvae and pupae of Trichoptera

The abdominal lateral line system in Trichoptera, consisting of filaments and lamellae with associated primary and secondary setae, was studied in larvae and pupae of 70 genera representing 26 families. Filaments are slender, generally bifid, tubular extensions of the cuticle that together form a fringe on the lateral abdominal surface of larvae and pupae of many but not all families of case-making Trichoptera (Integripalpia). Larvae and pupae of the Annulipalpia and Spicipalpia lack a lateral fringe of bifid filaments, but single filaments occur in larvae of a few unrelated genera. A lateral fringe may help in regulating the flow of water which is maintained through the case by abdominal undulation. Lamellae occur only in larvae of the Integripalpia, where they are variously distributed among families and genera, and probably have a sensory function. Three types of lamellae are recognized: forked, serrate and single. Filaments and lamellae have significant taxonomic value, and their patterns of occurrence raise questions about the phylogeny of Trichoptera.