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This paper is another contribution to knowledge of the caddisfly fauna of India. We redescribe and illustrate Diplectrona marginata Betten 1909 based on previously collected material as well as from fresh collections. The status of D. marginata is validated after Betten (1909) and Martynov (1935) and a neotype is designated for D. marginata because the remaining syntype has been damaged and is not identifiable. Furthermore, D. kinulta Oláh et al. 2020 is considered a synonym of D. marginata based on the similarity of male genitalia. Diplectrona aurovittata (Ulmer 1906) is reported for the first time from India, bringing the number of Indian species of Diplectrona to 10.

The history of studies on Australian caddisflies in the hydropsychid subfamily Diplectroninae is outlined against a broader background of uncertainties in the delineation of the worldwide type genus, Diplectrona Westwood. For the Australian fauna, keys are given to genera of Diplectroninae that occur in Australia and to adult males of species in Diplectrona (including a newly synonymised genus, Diemeniluma Neboiss), Austropsyche Banks, and Arcyphysa gen. nov. Of the 32 diplectronine species recognised, six are referred to each of Diplectrona and Austropsyche, among them one and four newly described species, respectively; and four established species are transferred from Diplectrona to Arcyphysa gen. nov., to join 16 newly described species. Diplectrona cognata Banks is synonymised with D. spinata Banks and Diplectrona bispinosa Jacquemart with Austropsyche victoriana Banks. Diagnoses and descriptions are accompanied by line drawings illustrating most of the diagnostic features of the genera and of most species, supplemented by photographic images. Australian species of Diplectrona are found from south-eastern Queensland to Tasmania, but neither Austropsyche nor Arcyphysa is known from Tasmania. Austropsyche extends from the Grampians in south-western Victoria to south-eastern Queensland, and the majority of species of Arcyphysa are recorded from north-eastern mainland Australia.

Subfamily-level groups of the Hydropsychidae Curtis are reassessed, using phylogenetic principles sensu Hennig for the first time. A historical overview of the Hydropsychinae Ulmer and the inconsistent placement of Smicridea McLachlan and allied genera is presented. The subfamily Hydropsychinae as presently defined is found to be paraphyletic. The study establishes monophyly of Hydropsychinae, confirms Macronematinae Ulmer plus smicrideine genera as the sister group, and investigates the status of the Smicrideini Flint 1974 within the family. Diplectrona zealandensis Mosely and Kimmins is found to be the sister group of Smicridea and allies. Hydropsychoidea sensu Weaver and Morse (1986, Journal of the North American Benthological Society 5:153) exclusive of Hydropsychidae are used as outgroup taxa. Analysis based on all larval instars suggests direction of character evolution for certain characters. A proposal is made for removal of the genera Smicridea, Smicrophylax Neboiss, and Asmicridea Mosely and Kim...

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.