Comparative dentition in free-living bird nest astigmatan mites

The chelal moveable digit patterns of seventeen free-living astigmatan mite species commonly found in bird nests are decomposed into functional groups using the scoring of observed asperities in order to explain the mites' coexistence in that commensal community. Type 'A' (tearing hook-like) and Type 'B' (nibbling) moveable digit morphotypes are found and the default durophagous 'Bauplan' of the mastication surface is described in great detail. The angles of mastication surface features are important and suggest that asperities are adapted to handle aggregate material. The mites' cutting and crushing moveable digit is asymmetrically designed anterior→posterior. Stochastically the mastication surface of the moveable digits of bird nest astigmatans map between International Roughness Grade Numbers N5 to N7 suitable for fine grinding. Various gripping and bladed adaptations for browsing, scooping and scraping are highlighted. Miniaturisation reduces the opportunity for trophic design space differentiation. Examples of underbite suitable for levering up material are found. Blunt and shallow features (i.e., 'pads') may be suitable for contact with and the gripping of compliant or wetted material. The function of digit tips is discussed. Aleuroglyphus ovatus is a crusher. Chortoglyphus arcuatus is a chewer. Some glycyphagid moveable digits approximate saw designs. Acarus farris is highly variable around a plesiomorphic form. The differentiated surface of Tyrophagus putrescentiae proximal to the condyle adapted for specialised gleaning is confirmed. Some species have a derived form proximally with a 'latch' comprised of an almost right angled zenith tooth and a very strong 'pocketed' gullet just before the end of the mastication surface for 'snapping' material. The detailed pattern of gullets is more nuanced across species than the pattern for teeth. Rhizoglyphus robini showed adaptations to deal with plant material. Dermatophagoides pteronyssinus is designed unusually. Nematophagy is discussed. Of the taxa reviewed, it only remains unclear how Tyrophagus palmarum and Tyrophagus similis morphologically avoid direct trophic competition in this habitat.