The Cephalic Morphology of Protopselaphus-A Phylogenetic Connecting Link in Staphylinidae (Coleoptera).

The head morphology of an ethanol-preserved specimen of Protopselaphus was examined using synchrotron µCT and SEM. The morphology, including muscles, nervous system, digestive tract and glands, is described in detail for the first time. We interpret the observed external and internal features with respect to their possible phylogenetic implications, mainly focused on the groundplan of the clade Protopselaphinae + Pselaphinae, and on apomorphies of the latter group. Whereas a clade Dasycerinae + (Protopselaphinae + Pselaphinae) is still not strongly supported morphologically, the monophyly of Protopselaphinae + Pselaphinae is robustly established. Adult cephalic synapomorphies are vertical tentorial columns completely detached from the tentorial bridge and dorsally firmly connected with the head capsule, a brain shifted to the narrowed neck region and filling out this space almost completely, and strongly developed labio-hypopharyngeal glands. Predacious habits and correlated falcate mandibles are also likely a groundplan apomorphy of this clade. Enlarged maxillary palps are arguably a typical feature but this condition varies strongly in the subfamily and also within Staphylinidae. Pselaphinae are characterized by several cephalic apomorphies such as a thin (or anteriorly obliterated, or missing) anterior tentorial arm, an antennal insertion covered by a frontal projection, a labral gland, a thin apical sensillum on the terminal maxillary palpomere, a highly reduced labial palpomere 3, and M. frontopharyngalis posterior composed of only one subcomponent.