A review of present knowledge of larvae of the Calopterygoidea (Zygoptera) of the Oriental realm, including keys to families and known genera Author Orr, Albert G. W. text Zootaxa 2024 2024-08-23 5497 2 209 243 http://dx.doi.org/10.11646/zootaxa.5497.2.3 journal article 305046 10.11646/zootaxa.5497.2.3 97257e17-d512-4a6e-a85b-b6af22d488fd 1175-5326 13618317 B3C66D95-3585-4920-BE93-A44D33FB2FBB Euphaea With 35 species ranging from Japan to Sri Lanka in the west to the Alor Archipelago in the Lesser Sundas and the Philippines in the east, Euphaea is by far the most speciose genus of the family and the most morphologically diverse in the adult stage. A habitus of the larvae of E. splendens Hagen , first mentioned by Hagen (1880) , was first illustrated with fair accuracy in Packard (1898) and Ris (1912) described and figured very accurately diagnostic features of E. variegata Rambur larva from Java. Tillyard (1917) depicted the lateral habitus of Euphaea ? variegata (as Pseudophaea sp. ) based on a photograph sent by F. Ris. Fraser (1929b) crudely figured the ventral habitus of E. splendens (as Pseudophaea , wrongly depicting exaggerated abdominal gills on S1–7) and the dorsal habitus of E. fraseri (Laidlaw) which also suggests the abdominal gills are on S 1–7 which are incorrectly described as ‘S’ shaped in both species, which may have been an artefact of preservation. A slightly improved version of the E. fraseri habitus was depicted in Fraser (1934) . Some structural details, photographs of the habitus and ecological information were provided for E. splendens larva by St Quentin (1973) . Other species that have been described and/or illustrated include: E. decorata Hagen ( Fig. 59 ), habitus and diagnostic details figured ( Tam et al . 2011 , Xu 2017 ); E. formosa Hagen , diagnostic details figured ( Matsuki & Lien 1978 ); E. impar Selys , photograph of habitus ( Ngiam & Ng 2022 ); E. ochracea Selys , habitus and diagnostic details, the former suggests the filament of the caudal gills is constricted at the base, which seems likely to be an artefact of preservation or artistic licence ( Matsuki 2001 ); E. opaca Selys , photograph habitus ( Zhang 2019 ); E. refulgens Hagen , habitus figured ( Needham & Gyger 1939 ); E. subcostalis Selys , habitus figured (as Euphaea sp. ), Orr (2003) ; E. superba Kimmins 1936 , habitus and diagnostic details figured ( Wu et al . 2019 ); E. tricolor Selys , habitus in life, Orr (2003) ; Euphaea yayeyamana Oguma , habitus and diagnostic details ( Ishida et al . 1988 , Ishida 1996 , Sugimura et al. 1999). The larva of E. masoni Selys was partially figured by Boonsoong (2016) , who documented its phoretic associations with chironomid larvae in streams in western Thailand . Larvae in the genus are typically squat and heavily built, but may vary in some characters, especially the form of the caudal gills. The head tends to be rather square with strong postocular lobes and the antennae are about the same length as or a little longer than as the distance from the posterior occipital margin to the base of the labrum ( Fig. 65 ); the inner apical process on the labial palp is well-developed, free and securiform in species examined ( Fig. 74 ), as in most Bayadera , from which they differ in not possessing a wavy outer margin to the outer process. Strong subocular spines on the gena range from 2–5 ( Keetapithchayakul et al . 2020 ). the male genital apophyses are very short and triangular or atrophied; the short, saccoid caudal gills often bear a long filament tapering abruptly from the main sac, but sometimes are more elongate with a pale cone-like process (especially in E. superba , and to some extent in E. tricolor and E. opaca ) which is more characteristic of Bayadera . Larval habitats of Euphaea species are quite variable, given the geographic and taxonomic range of the genus, but most occur at lower elevations (below 1000m ) in forested or sometimes open streams where the larvae tend to be found under stones in riffles and towards the centre of streams. In Brunei , for example, four species occur below 100m asl with habitat segregation evident between sister species; E. tricolor inhabits the main stream on the Sungei Belalong with larvae almost aways found under stones in a shallow riffle midstream whereas E. subcostalis is only found on small steep side streams leading into the main flow and the microhabitats of the adults also virtually abut each other ( Orr 2001 ).