Platycnemididae

Members of Platycnemididae are small to medium-sized damselflies, typically slender-bodied and associated with streams and rivers.^[4][5] The family is distributed throughout the Old World, particularly in tropical regions of Africa, Asia and the western Pacific.^[4]

Adults are diverse in appearance, but many species have laterally expanded heads and long tibial spines.^[4] In some groups, particularly the subfamily Platycnemidinae, the tibiae of the middle and hind legs are broadened and often conspicuously coloured, a feature that inspired the family name.^[5][9] Other members lack expanded tibiae and may differ greatly in body shape and colouration.^[5]

The aquatic larvae possess three caudal gills and are typically associated with flowing freshwater habitats.^[5] In some genera the gills are modified into distinctive forms, including fringed or ruff-like structures.^[4]

The family takes its name from the genus Platycnemis, whose name refers to the expanded tibiae characteristic of many members of the group. In 1840, Toussaint von Charpentier provided an etymology and diagnosis of the genus.^[9]

In 1904, Bianchi recognised Platycnemidinae as a distinct subfamily of damselflies, including the genera Platycnemis and Psilocnemis.^[1] During the twentieth century the group was generally treated as the family Platycnemididae. F. C. Fraser(1957) divided the family into two subfamilies, Platycnemininae and a broadly defined Calicneminae, noting that the latter was a heterogeneous assemblage whose relationships were not yet fully understood.^[5]

Molecular phylogenetic studies later demonstrated that the traditional classification did not accurately reflect evolutionary relationships. Dijkstra and colleagues (2014) incorporated the Old World taxa formerly placed in Protoneuridae within an expanded Platycnemididae and recognised several subfamilies, including Allocnemidinae, Calicnemiinae, Disparoneurinae, Idiocnemidinae, Onychargiinae and Platycnemidinae.^[4] Subsequent phylogenomic studies have supported the monophyly of Platycnemididae and its placement within Coenagrionoidea.^[8]

The following genera are currently placed in Platycnemididae.^[2][10]

The following fossil genera have been assigned to Platycnemididae:

• † Cretadisparoneura Huang et al., 2015 Burmese amber, Myanmar, Cenomanian
• † Palaeodisparoneura Poinar, Bechly & Buckley, 2010 Burmese amber, Myanmar, Cenomanian
• † Yijenplatycnemis Zheng et al., 2017 Burmese amber, Myanmar, Cenomanian

The family name Platycnemididae is derived from the type genus Platycnemis, with the standard zoological suffix -idae used for animal families.

The genus name Platycnemis is derived from the Greek πλατύς (platys, "broad" or "flat") and κνημίς (knēmis, "leg" or "shin"), referring to the expanded tibiae characteristic of many species.^[9][12]

• List of damselflies of the world (Platycnemididae)
• List of Odonata species of Australia