Larvae of the caddisfly suborder Integripalpia normally pupate in the last instar larval tube-case. Measurements of case structures show that larvae of Micrasema longulum differ in adding a long parallel-sided anterior section to their tube-cases, shortly before pupation. They pupate in the newly built section, discarding the slightly conical larval case. Literature data suggest that two additional species of Micrasema exhibit similar behaviour. Production of a special section of tube-case for pupation is reminiscent of the situation in the primitive suborders Annulipalpia and Spicipalpia which build a pupal case which is often the only construction during the entire life cycle. It is uncertain if the behaviour of Micrasema is atavistic, or if it developed independently.
