A comparative study of the morphology and distribution of setae and hairs on the larval legs of two families (Perlodidae, Perlidae) of Japanese Plecoptera

Abstract

A scanning electron microscope (SEM) was used to investigate the morphology and distribution of setae and hairs on the larval mid leg femur, tibia, and third tarsomere in representatives of six genera of Perlodidae and Perlidae. On the ventral surfaces of these leg segments we observed previously described clothing hairs, spine-like setae, and pinnate setae. We describe for the first time a new type of seta that we refer to as candle-like seta. Distinct differences in the distribution of hairs and setae are exhibited between the two families. Perlidae have hairy legs and on the femur the percentage of setae as compared to that of the clothing hairs is very high. Perlodidae are less hairy and on the femur the percentage of setae as compared to clothing hairs is much lower. The distribution of setae and hairs is similar among genera in the Perlidae, but not between genera of the Perlodidae. Pinnate setae are observed only in Neoperla geniculata. We discuss the types of setae and their distribution on the larval legs that characterise the families in relation to their habitats as well as to their behaviours observed in an aquarium using a video camera.