Blasticotomidae Thomson 1871

Family Blasticotomidae Thomson, 1871 (= Xyelotomidae Rasnitsyn, 1968) Type genus: Blasticotoma Klug * 1834. Diagnosis: Antenna with the first flagellomere several times longer and much thicker than following thread segments (reduced to one or no segments in Cenozoic Blasticotominae). Wing venation characteristically tenthredinoid (with 2r-rs joining cell 3rm rather than 2rm) and complete (except for forewing with vein 2-RS lost in Cenozoic Blasticotominae). Larva endophytic (feeding within fern stems)* with stemma touching antennal base dorsally* antenna setiform and consisting of six or seven segments. Legs setiform and six-segmented* with no prolegs present. Abdominal sterna dissected with transverse* oblique and longitudinal folds. Posterior terga sclerotized* concave and furnished with marginal processes. Composition: The family is composed of four subfamilies: Blasticotominae Thomson * 1871* Dahurotomidae subfam. nov. * Pseudoxyelocerinae subfam. nov. * and Undatominae subfam. nov. * and the unplaced genus Zippelia Rasnitsyn & Müller * 2023* known only from a larva. Remarks: The reasons to synonymize Xyelotomidae under Blasticotomidae are explained by Rasnitsyn and Müller (2023). In short* it is because of the high similarity of adult and particularly of larval morphology of the Mesozoic Xyelotomidae and Cenozoic Blasticotomidae. Under the resulting broader understanding of the family* it differs from other tenthredinoid families in having its flagellum differentiated into a long and thick basal segment and a thin segmented thread* except for some Cenozoic genera that have lost the thread-like antennal segments in Argidae and Zenargidae (for the latter* cf. Malagón-Aldana et al. 2021 a* b* Malagón-Aldana et al. 2022). However* Blasticotomidae differ from Argidae and Zenargidae in having a more complete wing venation and particularly in the forewing crossvein 2r-rs is always present (vs. lost in Argidae).