External and internal head structures of adults of Orchymontiinae, Prosthetopinae, Hydraeninae and Ochthebiinae were studied and those of Ochthebius semisericeus and Limnebius truncatellus are described in detail. The results are evaluated with respect to their relevance for a reconstruction of hydraenid phylogeny and also compared with structural features found in adults of other staphyliniform families. The monophyly of Hydraenidae is supported by the presence of a plate-like, trilobed premento-hypopharyngeal extension, an unusual origin of m. tentoriohypopharyngalis, dorsal tentorial arms firmly fused with the head capsule, modified basal antennomeres, and palpigers connected by a transverse sclerotized bar. Orchymontiinae are monophyletic and the basal sister group of the remaining Hydraenidae. The presence of a ventral transverse genal bulge and of a pubescent antennal club with more than two antennomeres (reversal in some prosthetopines: e.g. Mesoceration abstrictum) are possible apomorphies of Hydraenidae excluding Orchymontiinae. Prosthetopinae are probably monophyletic and the sister group of Ochthebiinae + Hydraeninae. The latter clade is characterized by a distinct cupula formed by antennomere VI, a loose five-segmented pubescent antennal club, and a modified antennal musculature. The presence of an unusual tentorio-pharyngeal dilator is a shared derived feature of Ochthebiinae and the genus Davidraena. The monophyly of Ochthebiinae was confirmed and Ochtheosus is the sister group of the remaining ochthebiine genera, which are characterized by a perforated wall-like structure formed by the posterior tentorial arms. The absence of this tentorial modification and the fimbriate galea are plesiomorphies retained in Ochtheosus. Calobius differs strongly from other subgenera of Ochthebius and a generic status may be appropriate. The monophyly of Hydraeninae is not supported. Hydraena was confirmed as a clade and Laeliaena and Limnebius are sister groups. The latter genus is characterized by several autapomorphies. The basal position of Orchymontiinae and Prosthetopinae suggests a Gondwanan origin of Hydraenidae and a primary preference for life in running water. Important evolutionary changes of head structures are complex transformations of the antennae and related structures. Yet, the use of the antennae as accessory breathing organs is not a groundplan feature of the family. The results of this study strengthen the case of staphylinoid affinities of Hydraenidae.

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Abstract. Adult head structures of Lepicerus inaequalis were examined in detail and interpreted functionally and phylogenetically. The monogeneric family clearly belongs to Myxophaga. A moveable process on the left mandible is an autapomorphy of the suborder. Even though Lepiceridae is the "basal" sistergroup of the remaining three myxophagan families, it is likely the group which has accumulated most autapomorphic features, e.g. tuberculate surface structure, internalised antennal insertion, and a specific entognathous condition. Adults of Lepiceridae and other myxophagan groups possess several features which are also present in larvae (e.g., premental papillae, semimembranous mandibular lobe). This is probably related to a very similar life style and has nothing to do with "desembryonisation". Lepiceridae and other myxophagans share a complex and, likely, derived character of the feeding apparatus with many polyphagan groups (e.g., Staphyliniformia). The mandibles are equipped with large molae and setal brushes. The latter interact with hairy processes or lobes of the epi-and hypopharynx. This supports a sistergroup relationship between both suborders.

Coleopterida (Coleoptera + Strepsiptera) has been established as the sister group of Neuropterida (Megaloptera + Neuroptera + Raphidioptera) based on recent phylogenetic analyses of DNA sequence data obtained from genomes and transcriptomes. However, within the resulting clade (Neuropteroidea) the proposed sister-group relationship between the highly specialized endoparasitic Strepsiptera and the megadiverse Coleoptera still lacks convincing morphological support. Furthermore, relationships among the four suborders of Coleoptera remain controversial, with morphological characters strongly conflicting with results suggested by molecular evidence. A large morphological dataset comprising external and internal features of adults and immature stages is presented here and analysed phylogenetically. Our study is focused on deep splits in Coleopterida and on reconstructing character evolution on the phenotypic level. Parsimony analyses clearly support a sister-group relationship between Strepsiptera and monophyletic Coleoptera. Presumptive synapomorphies are characters linked with posteromotorism, but also features of the head and prothorax. We recover Archostemata as sister group of the remaining extant Coleoptera, and Polyphaga as sister group of the species-poor suborder Myxophaga. The most important character complex of Coleoptera is heavy sclerotization without exposed membranes and a simplification of the thoracic muscle apparatus. Non-archostematan beetles are characterized by further simplifications of the thoracic locomotor apparatus. This trend reaches its peak in Myxophaga and Polyphaga, and these suborders also share apomorphies of the larval legs. A pattern with Polyphaga as sister to all other suborders and a clade Myxophaga + Archostemata (as in recent molecular phylogenetic studies) requires ten additional steps with our dataset. This scenario implies that various simplifications of the thoracic exoskeleton and musculature have taken place several times independently, and also that a complex feeding apparatus suitable for saprophagy and sporophagy was ancestral in Coleoptera, with secondary reduction (or modification) in Archostemata and Adephaga. The coleopteran subordinal relationships remain a challenge, with morphological and molecular data suggesting distinctly different patterns. The earliest evolution of Coleopterida is not documented in the fossil record. The exploration of potential stem-group fossils is a high priority, as is the study of species from the Permian-Triassic transition zone, which are apparently important in the context of evaluating the relationships among beetle suborders.

External and internal structures of the head of adults of Clambus are described and illustrated in detail. The results are compared with structural features found in the clambid genus Calyptomerus, in representatives of other scirtoid families, and also in species of other coleopteran suborders, notably Myxophaga. The results tentatively support the monophyly of Scirtoidea and a close relationship between Clambidae and Eucinetidae is suggested by one shared derived feature of the mandible, a long and slender apical tooth with a serrate edge. The monophyly of Clambidae is very strongly supported and Acalyptomerus is probably the sistergroup of a clade Calyptomerus + Clambinae. Potential scirtoid autapomorphies are the loss of the dorsal tentorial arms, a bulging gula, a strongly transverse labrum, and a ridge separating the mediostipes from the lacinia. However, all these features are homoplasious. The monophyly of Clambidae is supported by modifications of the head capsule which is strongly flattened and broadened, by a deep clypeofrontal incision enabling vertical antennal movements, and a series of antennal features. Synapomorphies of Clambinae + Calyptomerus (Clambidae excluding Acalyptomerus) are the conglobate body form with the ventral side of the head capsule in contact with the mesocoxae, and compound eyes integrated in the contour of the head. The completely subdivided eye is an autapomorphy of Clambus. An entire series of features is shared by Clambidae (or Scirtoidea) and Myxophaga. Most of them are apomorphies that apparently evolved independently in both groups. However, the presence of well‐developed maxillary and labial glands is arguably a retained groundplan feature of Coleoptera, with parallel loss in Archostemata, Adephaga and various groups of Polyphaga. J. Morphol. 277:615–633, 2016. © 2016 Wiley Periodicals, Inc.