Heminemourinae, a New Subfamily of Stoneflies in Eocene Baltic Amber (Plecoptera: Nemouridae)

A new subfamily of the stonefly family Nemouridae, Heminemourinae subfam. nov., along with a new genus and species, Heminemoura triloba gen. et sp. nov., are described and illustrated from the Eocene Baltic amber. The new subfamily is characterized by the loss of cervical gills and the female pregenital plate, presence of two RP-M crossveins, and the mutual touching of AA1 and AA2 in the forewing, which are neither fused nor parallel. Additionally, the new stonefly exhibits a well-developed sternum 8 and subgenital plate. Heminemoura gen. nov. is distinguished from other nemourid genera by its unique combination of wing venation and female terminalia morphology.