The strange holometabolan beak larva from about 100 million years old Kachin amber was physogastric and possibly wood-associated

The group Neuropteriformia (beetles, lacewings, etc.) is today very species-rich, but also has a good fossil record in the Mesozoic. Amber provides not only adults, but also fossil larvae; some of these fossil neuropteriformian larvae have very unusual morphologies not seen in the modern fauna. We here report an unusual new fossil neuropteriformian larva. The mouthparts form a beak. Fossil larvae with similar mouthparts are known, and it seems that this new larva is a representative of the species ?Partisaniferus edjarzembowskii. The new larva, unlike the already known ones, has a large and inflated trunk. Based on comparison with extant larvae, such an inflated trunk should be considered physogastric. The new larva is only the second case of physogastry in fossil holometabolan larvae. Also early larvae of this species are known. The strong difference between the different larval stages give reason to interpret the ontogeny hypermetamorphic. Also this phenomenon is in fact very rare in the fossil record; most earlier candidates remain assumptions without further substantiation. Physogastry in larvae is often coupled to a mode of live in confined spaces, for a fossil preserved in amber this may mean living inside wood. Feeding mode might have been predatory, but could also have been feeding on fungi.