New insights into a life in current: do the gill lamellae of Epeorus assimilis and Iron alpicola larvae (Ephemeroptera: Heptageniidae) function as a sucker or as friction pads?

Epeorus assimilis and Iron alpicola larvae inhabit swift running waters where they scrape algae from the stories. Previous authors Suggested that the gill lamellae are modified to a Sucker as an adaptation to withstand Currents. Video observations show that the gill lamellae stay tilted in strong currents. Larvae can attach to the surface without any problem even if single gill lamellae are missing and therefore no negative pressure can be developed. Consequently, gill lamellae cannot have a Sucker function. SEM analysis reveals areas with spike-shaped microtrichia on the abdominal sternites and setose pads ventrally oil the gill lamellae. These setose pads look very similar to those described in some terrestrial insects. Setae of I. alpicola have a similar size, but a higher density than those of E. assimilis, what might cause a greater adhesive strength and could be an adaptation to the swifter Currents in which the latter species lives.