Structure and Evolution of Mouthparts in Coleoptera

Profound head modifications in Claviger testaceus (Pselaphinae, Staphylinidae, Coleoptera) facilitate integration into communities of ants

“…The maxillary groove (= fossa maxillaris; see, e.g., Dressler & Beutel, 2010; Beutel & Yavorskaya, 2019) is lacking; the small maxillae (Figures 3a–c and 4e) are inserted between the lateral base of the mentum and the lateral edge of the anteromedian emargination of the ventral wall of the head capsule. The well‐developed cardo is roughly semicircular and bears a distinct internal process with a lateral and a mesal branch; setae are absent.…”

“…The extremely long and dense distal setae of the lacinia and galea, projecting far beyond the mandibles, form a licking/‘sponging’ capillary apparatus, which is lacking in all beetles with predacious or fungivorous feeding habits (Beutel & Yavorskaya, 2019). A small ventral area of the lacinia is fused with the hypopharynx, a modification unknown in any other beetles (e.g., Beutel & Yavorskaya, 2019). Dissections of seven free‐living pselaphine species (illustrated in Figures S3 and S4) revealed in each case that the lacinia is not fused or connected with the hypopharynx.…”

“…This is in clear contrast to most other Pselaphinae, which have large, exposed mandibles, tetramerous and long maxillary palps (e.g., Figures S1c, S3, and S4), and dimerous labial palps inserted on a well-developed prementum (e.g., Figures S3b,d,g and S4b,d). The mouthparts of Claviger strongly deviate from those of free-living beetles (e.g., Antunes-Carvalho et al, 2017;Beutel & Yavorskaya, 2019;Newton & Thayer, 1995), and also from those of myrmecophilous non-Clavigeritae pselaphines. The labrum bears a pair of openings for the labral glands, whose secretion was previously found to attract ants and to trigger regurgitation (Cammaerts, 1974).…”

“…The function of the maxillae is integrated with that of the labrum and mandibles. The extremely long and dense distal setae of the lacinia and galea, projecting far beyond the mandibles, form a licking/'sponging' capillary apparatus, which is lacking in all beetles with predacious or fungivorous feeding habits (Beutel & Yavorskaya, 2019). A small ventral area of the lacinia is fused with the hypopharynx, a modification unknown in any other beetles (e.g., Beutel & Yavorskaya, 2019).…”

“…Because of an enormous morphological diversity, a large number of genera and tribes included in Pselaphinae, and the still poorly understood phylogeny, we do not attempt a detailed and formal reconstruction of the pselaphine morphological groundplan. Instead, we compare structures found in C. testaceus to the coleopteran groundplan (e.g., Beutel & Yavorskaya, 2019) and conditions found in less specialized staphylinoid beetles (e.g., Weide & Betz, 2009) including Protopselaphus , wherever relevant in the context of specialized feeding adaptations.…”