Spathiopterygid wasps represent an enigmatic group within Proctotrupomorpha, characterized by their minute size, their peculiar forewings with reduced venation and a pattern of microtrichiae, and highly reduced or absent hind wings. This family is known exclusively from Cretaceous ambers (ranging from the Barremian to the Santonian) and shows a wide geographic distribution. Specimens of this family are rare, and most of the species are only known from their holotypes, limiting our understanding of sexual dimorphism and intraspecific variability. Here, we describe Karaweik splendida & Aacute;lvarez-Parra & Jouault gen. et sp. nov. from mid-Cretaceous Kachin amber, bringing the known paleodiversity of Spathiopterygidae to nine species distributed in seven genera. An updated species checklist and key are provided. We discuss the different nomenclatures for forewing venation used for the family and propose the term "pseudoveins" for what appear to be spectral veins, represented by rows of microtrichiae or membrane wrinkles. The studied specimen is anatomically compared with the other representatives of the family. We also address the potential belonging of Cretapria tsukadai Fujiyama, 1994, from Aptian Choshi amber in Japan, to Spathiopterygidae. The new species has tooth-like structures on the posteroventral part of the head, which may be related to a parasitoid behavior or wood-dwelling habit. Furthermore, we briefly comment on the paleobiology of the family and compare the possible flight modes of spathiopterygids with those of mymarids and mymarommatids.