Gastric mill structure and its phylogenetic significance in larval Hydropsychidae (Trichoptera)

Gastric mills of final instar larval Hydropsychidae (21 genera: 59 species) observed by scanning electron microscopy, revealed dramatic structural variation. There was no dental development in Diplectrona (S. F. Diplectroninae ), minute spines in Aphropsyche, Austropsyche, Homoplectra (S. F. Diplectroninae ), Arctopsyche and Parapsyche (S. F. Arclopsychinae ), and well-developed sclerotized teeth in most genera of Hydropsychinae and Macronematinae. Hydropsyche and Ceratopsyche were characterized by 30–50 triangular tooth-plates. Only two genera in the Hydropsychinae possessed a constant number of teeth in the proventriculus - Synaptopsyche with 36 and Potamyia with 18. Gastric mills of Cheumatopsyche contained larger numbers of smaller, spine-covered teeth whereas in Smicridea teeth were absent. Within the Macronematinae, species of Macrostemum, Blepharopus, Protomacronema, Amphipsyche and Aethaloptera invariably had 18 tooth-plates while Polymorphanisus possessed 12 smaller, sharply triangular teeth. Leptonema, Macronema and Plectromacronema all had spinate proventriculi. In general the degree of dental development within subfamilies supports currently held views on hydropsychid phylogeny. I suggest that the development of large tooth-plates for food processing has contributed significantly to the adaptive radiation of the more highly evolved Hydropsychinae and Macronematinae. Examination of gut contents from Amphipsyche meridiana indicated differential crushing efficiency of diatoms and dinoflagellates. Further studies are required to determine the functional role of the dentition in each type of mill.