An unusual 100-million-year old holometabolan larva with a piercing mouth cone

PeerJ. 2020 Apr 3:8:e8661. doi: 10.7717/peerj.8661. eCollection 2020.

Abstract

Holometabola is a hyperdiverse group characterised by a strong morphological differentiation between early post-embryonic stages (= larvae) and adults. Adult forms of Holometabola, such as wasps, bees, beetles, butterflies, mosquitoes or flies, are strongly differentiated concerning their mouth parts. The larvae most often seem to retain rather plesiomorphic-appearing cutting-grinding mouth parts. Here we report a new unusual larva preserved in Burmese amber. Its mouth parts appear beak-like, forming a distinct piercing mouth cone. Such a morphology is extremely rare among larval forms, restricted to those of some beetles and lacewings. The mouth parts of the new fossil are forward oriented (prognathous). Additionally, the larva has distinct subdivisions of tergites and sternites into several sclerites. Also, the abdomen segments bear prominent protrusions. We discuss this unusual combination of characters in comparison to the many different types of holometabolan larvae. The here reported larva is a new addition to the 'unusual zoo' of the Cretaceous fauna including numerous, very unusual appearing forms that have gone extinct at the Cretaceous-Palaeogene boundary.

Keywords: Convergence; Evolution; Holometabola; Insecta; Mouth parts.

Grants and funding

Joachim T. Haug is funded by the Volkswagen Foundation with a Lichtenberg Professorship. Carolin Haug was funded via the LMUexcellent Junior Researcher Fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.