A New Genus and Species of Syspastoxyelidae (Hymenoptera) from Mid-Cretaceous Burmese Amber

Syspastoxyelidae is an extinct basal hymenopteran lineage currently known only from mid-Cretaceous Burmese amber. Here, we describe a new genus and species, Cilioxyela setosa gen. et sp. nov., based on a well-preserved female specimen from the Hukawng Valley, northern Myanmar. The new taxon is assigned to Syspastoxyelidae based on diagnostic characters, including strongly proximally condensed forewing venation, a composite first flagellomere formed by fused ancestral segments, tibiae bearing dense robust spines, and segmented cerci. Cilioxyela gen. nov. differs from all previously described genera by a unique character combination, most notably, a distal forewing veinless membrane lacking longitudinal corrugation and conspicuously elongated marginal setae, together with a narrowed forewing, elongate pterostigma and anal cell, and distinctive antennal segmentation. These features support the establishment of a new genus. Comparative analysis indicates that distal forewing morphology in Syspastoxyelidae is more variable than previously recognized. The presence or absence of longitudinal corrugation in the distal forewing membrane likely reflects genus-level differentiation rather than a stable family-level synapomorphy. The new genus also supports a tentative division of Syspastoxyelidae into at least two morphologically cohesive groups, pending testing through additional fossil discoveries and quantitative phylogenetic analyses. The discovery of Cilioxyela setosa expands the known morphological disparity of Syspastoxyelidae and highlights evolutionary plasticity in distal forewing architecture among early Hymenoptera, contributing to a better understanding of morphological diversification in mid-Cretaceous forest ecosystems.