The morphological diversity of long-necked lacewing larvae (Neuroptera: Myrmeleontiformia)

of diversity in the ecologically important group of Insecta (e.g. Hallmann et al. 2017, Lister & Garcia 2018, Seibold et al. 2019). To improve our understanding of this phenomenon, we can look at similar declines in diversity in ancient times as provided by the fossil record. In other words, we can compare the diversity of Insecta at different time slices. The fossil record of Insecta is especially attractive for such a type of comparison, as fossils with ex­ ceptional preservation, for example, preserved in amber, offer a very direct comparison to modern forms. A major share of the modern­day diversity of Insecta is in fact the diversity of its ingroup Holometabola, with far more than half a million described species (Grimaldi & Engel 2005). While the representatives of Holometabola are indeed very diverse, they share one characteristic feature: all immatures (besides the ultimate one) lack compound eyes, and instead (if not blind) possess special­ ised eyes, so­called stemmata (Beutel et al. 2013). Similarly to the fact that the diversity of Insecta is mainly the diversity of Holometabola, the diversity of Holometabola is factually the diversity of some major ingroups, also known as “the big four” (although also here the true diversity lies in some deeper ingroups): 1) Hy­ me noptera: bees, ants and other wasps; 2) Coleoptera: beetles; 3) Lepidoptera: butterflies and moths; 4) Diptera: mosquitoes, midges, gnats and flies. Each of the “big four” comprises more than 100,000 formally described species (Grimaldi & Engel 2005, Beutel et al. 2013, Engel et al. 2018). From an ecological point of view, we need to consider that the diversity of ecosystem functions is in fact not only represented by well­known adult forms of Holometabola (Grimaldi & Engel 2005, Marshall 2012, Hölker et al.