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Xenos vesparum of the highly specialized Strepsiptera is a new insect model in the context of host-parasite relationships. The endoparasitic female and male secondary larvae were studied using µCT, 3D-reconstructions, histology, and photomicrography. The infectious primary larva is followed by a trophic and endoparasitic secondary larval stage. In contrast to immature stages of other holometabolous groups, the second instar increases dramatically in size. Compound eyes and external wing anlagen are present in male larvae before the pupal stage. In contrast to the females, the brain of males bears well-developed optic neuropils and retinula cells are present. The cephalothorax is comparatively simple in the female larvae, yet distinctly more complex than in the adult, where most muscles are reduced. Large testes are present in male larvae and numerous oocytes in the females, but they are still immature. The larval features are discussed in the context of holome­tabolous development and heterochronic processes. Unique features of Strepsiptera are the early differentiation of the sexes and the occurrence of compound eyes and external wing anlagen in male secondary larvae. The phylogenetic position of Strepsiptera suggests that this is a secondary feature and thus an autapomorphy. To address mature females of Stylopidia as neotenic adults is an oversimplification. They display a mosaic pattern of paedomorphic characters such as features of the nervous system and the presence of stemmata, but also non-paedomorphic structures, such as the spiracles.

We document external and internal thoracic structures of the free-living pselaphine beetle Pselaphus heisei (Pselaphitae) using a set of traditional and modern techniques. Like in the specialized myrmecophile Claviger testaceus (Clavigeritae), the skeletal elements of the pro- and pterothorax are highly compact, with largely reduced inter- and intrasegmental sutures. Features previously listed as synapomorphies of staphylinid subgroups, to which Pselaphinae belong, are confirmed for P. heisei. The only previously proposed thoracic synapomorphy of Pselaphinae, the mesoventral foveae, is likely transformed in P. heisei: we assume that the concavities are directed mesad and internally fused, thus forming a broad channel ("perforation") extending through the keel-like median region of the mesoventrite. The prothoracic foveal system is strongly reduced, with only one pair of pits present in front of the procoxae. Their internal invaginations form a transverse ventral endoskeletal bar that stabilizes the prothorax. The condition observed in the free-living P. heisei is in contrast with previous hypotheses linking the reduction of the foveal system with myrmecophily. Moreover, traces of the mesoventral foveae are even preserved in the highly specialized inquiline C. testaceus. Gland cells are associated with areas of hyaline squamose setae on different body regions, suggesting release of secretions on the ventral side of the head, pro- and mesothorax, and abdominal base. Similar specialized setal patches are common in Pselaphini and related groups within Pselaphitae. The prothoracic musculature in P. heisei is more complex than that in the myrmecophilous C. testaceus and the free-living, unspecialized Creophilus maxillosus (Staphylininae). The metathoracic muscle system is strongly simplified, demonstrating that P. heisei cannot fly, even though wings, some skeletal elements of the flight apparatus, and some small direct flight muscles are preserved. It cannot be fully excluded that indirect flight muscles and thus a functional flight apparatus is preserved in a certain percentage of individuals.

The fossil record allows a unique glimpse into the evolutionary history of organisms living on Earth today. We discovered a specimen of the stem group ant †Gerontoformica gracilis (Barden and Grimaldi, 2014) in Kachin amber with near-complete preservation of internal head structures, which we document employing µ-computed-tomography-based 3D reconstructions. We compare †Gerontoformica to four outgroup taxa and four extant ant species, employing parsimony and Bayesian ancestral state reconstruction to identify morphological differences and similarities between stem and crown ants and thus improve our understanding of ant evolution through the lens of head anatomy. Of 149 morphological characters, 87 are new in this study, and almost all applicable to the fossil. †Gerontoformica gracilis shares shortened dorsal tentorial arms, basally angled pedicels, and the pharyngeal gland as apomorphies with other total clade Formicidae. Retained plesiomorphies include mandible shape and features of the prepharynx. Implications of the reconstructed transitions especially for the ant groundplan are critically discussed based on our restricted taxon sampling, emphasizing the crucial information derived from internal anatomy which is applied to deep time for the first time. Based on the falcate mandible in †Gerontoformica and other Aculeata, we present hypotheses for how the shovel-shaped mandibles in crown Formicidae could have evolved. Our results support the notion of †Gerontoformica as ‘generalized’ above-ground predator missing crucial novelties of crown ants which may have helped the latter survive the end-Cretaceous extinction. Our study is an important step for anatomical research on Cretaceous insects and a glimpse into the early evolution of ant heads.

The compressed directory in this upload includes all input and output files from the Bayesian analyses conducted in the study.

The mesosoma is the power core of the ant, containing critical structural and muscular elements for the movement of the head, legs, and metasoma. It has been hypothesized that adaptation to ground locomotion and the loss of flight led to the substantial rearrangements in the mesosoma in worker ants and that it is likely the ant mesosoma has undergone functional modifications as ants diversified into different ecological and behavioral niches. Despite this importance, studies on the anatomy of the ant mesosoma are still scarce, and there is limited understanding of important variation of internal structures across the ant phylogeny. Recent advances in imaging techniques have made it possible to digitally dissect small insects, to document the anatomy efficiently and in detail, and to visualize these data in 3D. Here we document the mesosomal skeletomuscular system of workers of the red wood ant, Formica rufa Linnaeus, 1761, and use it to establish a 3D atlas of mesosomal anatomy that will serve as reference work for further studies. We discuss and illustrate the configuration of the skeletomuscular components and the function of the muscles in interaction with the skeletal elements. This anatomical evaluation of a ‘generalized’ ant provides a template for future studies of the mesosoma across the radiation of Formicidae, with the ultimate objective of synthesizing structural, functional, and transformational information to understand the evolution of a crucial body region of ants.

It is generally assumed that Cretaceous stem ants were obligately eusocial, because of the presence of wingless adult females, yet the available evidence is ambiguous. Here, we report the syninclusion of a pupa and adult of a stem ant species from Mid-Cretaceous amber. As brood are immobile, the pupa was likely to have been transported by an adult. Therefore, the fossil substantiates the hypothesis that wingless females were cooperators, thus these were true ‘workers’. Re-examination of all described Cretaceous ant species reveals that winged–wingless diphenism – hence a variable dispersal capacity – may have been ancestral to the total clade of the ants, and that highly specialized worker-specific phenotypes evolved in parallel between the stem and crown groups. The soft-tissue preservation of the fossil is exceptional, demonstrating the possibility of analysing the development of the internal anatomy in stem ants. Based on the highest-resolution µ-CT scans of stem ants to date, we describe †Gerontoformica sternorhabda sp. nov., redescribe †G. gracilis, redefine the species group classification of †Gerontoformica, and provide a key to the species of the genus. Our work clarifies the species boundaries of †Gerontoformica and renders fossils relevant to the discussion of eusocial evolution in a way that has heretofore been intractable.

Pselaphinae is a large subfamily, comprising over 10 000 species of the megadiverse Staphylinidae (rove beetles). A remarkable feature of this group is the extreme structural diversity of different body regions, especially the head and its appendages. Within Pselaphinae, Clavigeritae stand out as a clade of highly specialized myrmecophiles. We examined internal and external head structures of the clavigerite species Diartiger kubotai Nomura, using state-of-the-art techniques. The cephalic morphology indicates in a phylogenetic context that the loss of eyes in some Clavigeritae was the latest of major evolutionary changes. We compiled the largest set of morphological data ever scored for the subfamily, comprising 155 characters of the head. Parsimony analyses and Bayesian inference yielded a similar phylogenetic pattern, largely congruent with results published previously. We retrieved Pselaphinae as a clade, and Faronitae as sister to all remaining groups of the subfamily. Faronitae are followed by a "Euplectitae grade" and non-monophyletic Goniaceritae, Batrisitae and Pselaphitae. Clavigeritae are monophyletic, but have evolved within the pselaphite grade. The enigmatic Colilodion Besuchet, recently shifted from Clavigeritae to a paraphyletic Pselaphitae, was placed as sister to extant clavigerites based on an array of cephalic synapomorphies. The current classification of Pselaphinae is unstable and deep changes should be made maintaining only monophyletic units, whereas most of the supertribes are paraphyletic. Characters of the head, with a concentration of mouthparts and sensory structures, and essential parts of the digestive tract and the nervous system, are highly informative phylogenetically. Study of internal structures, presently still at a very preliminary stage, obviously is essential for understanding the evolution of Pselaphinae. Future genetic investigations may reveal mechanisms behind the unique structural megadiversity in this exceptional group of rove beetles.

Ants are highly polyphenic Hymenoptera, with at least three distinct adult forms in the vast majority of species. Their sexual dimorphism, however, is overlooked to the point of being a nearly forgotten phenomenon. Using a multimodal approach, we interrogate the near total head microanatomy of the male of Dorylus helvolus, the "sausagefly," and compare it with the conspecific or near-conspecific female castes, the "driver ants." We found that no specific features were shared uniquely between the workers and males to the exclusion of the queens, indicating independence of male and worker development; males and queens, however, uniquely shared several features. Certain previous generalizations about ant sexual dimorphism are confirmed, while we also discover discrete muscular presences and absences, for which reason we provide a coarse characterization of functional morphology. Based on the unexpected retention of a medial carinate line on the structurally simplified mandible of the male, we postulate a series of developmental processes to explain the patterning of ant mandibles. We invoke functional and anatomical principles to classify sensilla. Critically, we observe an inversion of the expected pattern of male-queen mandible development: male Dorylus mandibles are extremely large while queen mandibles are poorly developed. To explain this, we posit that the reproductive-limited mandible phenotype is canalized in Dorylus, thus partially decoupling the queen and worker castes. We discuss alternative hypotheses and provide further comparisons to understand mandibular evolution in army ants. Furthermore, we hypothesize that the expression of the falcate phenotype in the queen is coincidental, that is, a "spandrel," and that the form of male mandibles is also generally coincidental across the ants. We conclude that the theory of ant development and evolution is incomplete without consideration of the male system, and we call for focused study of male anatomy and morphogenesis, and of trait limitation across all castes.

��� Archaeomalthus synoriakos Yan et al., gen. et sp. nov. (Figs. 1 and 2) Diagnosis As for the genus. Derivation of name The Greek-specific name ���synoriakos��� ��� ���borderline���, refers to the proximity of Babiy Kamen`locality to Permian-Triassic boundary. Material Holotype: PIN 4887/102, single specimen, counter print of the complete body impression with antennae and all legs missing. Repository: Paleontological Institute, Russian Academy of Sciences (curator Prof. Dr A.P. Rasnitsyn). Occurrence Babiy Kamen`locality, Tom`river, Kuznetsk Basin, S. Siberian, in the upper part of the Maltsevo Formation. Description Head slightly, ca. 0.23 mm, long and about as wide at the ocular region. Compound eyes round, located at anterior third of head, half as long as temporal region. Antennal insertion areas round, with outer margin bordered by fine carina. Antenna with small scapus, larger pedicellus with slightly rounded edges, and stout flagellomeres, apparently moniliform. The arrangement of apical mandibular teeth not recognizable. Prementum rather large, at least as wide as eye. Anterior angles of pronotum blunt, not protruding forward; pronotal disc distinctly convex; anterior pronotal margin with median subtriangular depression; posterior angles slightly protruding laterally. Propleuron narrow, triangular, obliterating on anterior third of prothorax. Elytra with fine lateral carina; epipleuron widest near humeral bulge, moderately wide on basal half, strongly narrowed posteriorly. Mesepimeron oblique, with slightly sinuated anterior and posterior margins. Mesocoxal pits closed laterally by mesepimeron and metanepisternum. Metanotum with distinct alacristae. Metanepisternum parallelogram-shaped. Metaventrite about as long as width between anterolateral edges, posterior edge about 1.5 times as wide. Procoxae transverse, mesocoxae almost globular, with inconspicuous lateral extension. Metacoxae short, with mesal part posteriorly rounded and extending through approximately two-thirds of first abdominal ventrite, only slightly narrowing laterally. Sternites II-IV distinctly longer than V-VII, gradually narrowing towards the abdominal apex. Short sternite VII with round median structure with unclear homology (apparently glandular opening). Terminal sternite VIII as long as VI and VII combined, with rounded hind margin. At least posterior abdominal sternites with narrow laterosternites.. Discussion Taxonomic position of Archaeomalthus In contrast to specimens of Micromalthus described from Miocene amber,which were not very different from the recent M. debilis H��rnschemeyer et al. 2010, Permian Archaeomalthus shows distinct differences compared to the Recent species and Cenozoic fossils of the family. Nevertheless, the affinities of extant Micromalthidae are suffi- cient for justified placement in this family. This includes a number of diagnostic features: a small and slender body, the large relative size of the head capsule, and well-developed, round compound eyes. Clear apomorphies shared with fossil and extant Micromalthus are shortened, quadrangular and posteriorly truncated elytra, leaving abdominal tergites V-VIII exposed, and the increased number of abdominal sternites, in contrast to five in ancestral Permian species (Stem group Coleoptera) and the vast majority of extant beetles (Ponomarenko 1969; Beutel et al. 2008; Lawrence et al. 2011). Additional potential apomorphies are the fusion of the labrum and clypeus, the long subparallel temporal region, the stout antennal flagellomeres, the semioval scutellar shield (Figure 1 (b)), and probably, weak sclerotization of the body. Considering the placement in Archostemata and the ground plan of this suborder (and Coleoptera s.l. (Beutel 1997; Beutel et al. 2008; Friedrich et al. 2009)), additional apomorphies shared with Micromalthus are the absence of cuticular tubercles and scales, the complete lack of dorsal cephalic protuberances, the absence of a constricted neck region, evenly sclerotized elytra lacking window punctures, the absence of the transverse ridge on the mesoventrite, the concealed metatrochantins (Beutel et al. 2008; H��rnschemeyer 2009) (Figures 1 and 2 (m,n)) and abdominal glands (Figures 1 (b) and 3) Shortened antennae, wings and legs of a Miocene micromalthid (lately Micromalthus anansi was synonymized with M. debilis by (H��rnschemeyer et al. 2010)) were considered as a step of progressing morphological simplification of adults (Perkovsky 2007). However, this term is problematic, as these features have obviously nothing to do with regressive character conditions occurring in beetles (e.g. Rempel and Church 1965, 1969, 1971; K��hne 1972; Kobayashi et al. 2013). It appears likely that small size, shortened elytra, and weakly sclerotized cuticle are related to the short lifespan and sporadic occurrence of adults, and their ���vestigial��� status in the context of reproduction (Pollock and Normark 2002; H��rnschemeyer et al. 2010). Relatively short legs are also common in other extant archostematan beetles including Permian forms (e.g. Ponomarenko 1969; see also Yan et al. 2017a) and moniliform antennae characterized as a plesiomorphic character by Perkovsky (2007). One of several distinct features of Archaeomalthus differing from Micromalthus is the presence of an exposed propleuron separated by distinct sutures. This is clearly a plesiomorphy corresponding to the autapomorphic fusion of all prothoracic sclerites in extant or Cenozoic species (e.g. Beutel et al. 2008; Friedrich et al. 2008). Two other conspicuous features are the presence of a very distinctly delimited groove on the mesoventrite and a corresponding anteromedian process of the metaventrite. Both features resemble conditions commonly found in Adephaga, notably the aquatic groups (excluding Gyrinidae) and basal grade Carabidae (Beutel 1992). However, a placement of Archaeomalthus in these suborders can be clearly excluded based on the short metacoxae without enlarged coxal plates, the lack of a prosternal process, and the increased number of abdominal sternites (e.g. Beutel 1992; Beutel and Haas 2000). The strongly developed process of the metaventrite, which widely separates the mesocoxae, is uncommon in recent Archostemata, even though it occurs in some extinct groups of this suborder, such as Schizophoridae (e.g Tersus Martynov, 1926) or Ademosynidae (Yan et al. 2017b). It is likely that this condition has evolved several times independently, in scattered groups of Archostemata including Micromalthidae, and also in Adephaga (e.g. Beutel 1986, 1992; Beutel and Haas 2000). In contrast to Archaeomalthus, the thoracic venter of Micromalthus appears distinctly simplified (Figures 2 (g���j,m,n)). It is conceivable that this is a reduction linked with the very limited role of the adults in the life cycle of the extant species. Despite the marked differences between Archaeomalthus and Micromalthus, the former already show a distinct and apparently very stable degree of deviation from the ground plan of Coleoptera s.str. and s.l. (e.g. Beutel 1997). The remarkable series of reductional features shared by the Permian fossil and the extant species include a lightly sclerotized body without any distinct surface sculpture, a head lacking dorsal protuberances, shortened and apparently thin elytra, exposed membranous areas behind the procoxae and between at least two basal visible abdominal sternites, and the reversal of the invagination of the terminal abdominal segments. It is likely that the reduced role of adults of Micromalthidae (Perotti et al. 2016) was a syndrome of vestigial characters acquired at least 255 million years ago. Evolutionary stability of Micromalthidae There are two main competing hypotheses to explain clades that accumulate phenotypic variation at a slow rate: the first one invokes genetic and developmental constraints that restrict the production of phenotypic variation (Smith 1981; Raff 1996; Gould 2002). The second explanation is that stasis is a result of stabilizing selection (Charlesworth et al. 1982; Kirkpatrick 1982; Estes and Arnold 2007). Exceptional evolutionary stability, bradytely, or ���arrested evolution��� (Simpson 1944) of Micromalthidae, resulted in very slow morphological change over time, which characterizes ���living fossils���. On principle, this could be due to very long periods of stable environmental conditions (H��rnschemeyer et al. 2010, see historical analysis of bradytely in Clarke and Chatzimanolis 2009). In the case of Micromalthidae this is the subcortical space of fungus-infested wood, which may have been one factor that buffered micromalthids from strong selection for morphological change (BuslovClarke and Chatzimanolis 2009). Almost any change, but particularly a major change, of the phenotype in such a well-balanced system will be deleterious. Although minor gene substitution may be frequent, the well-buffered system of developmental canalizations shields the phenotype from major changes. There is an opportunity for speciation, but a major alteration of the morphotype is impossible as long as the epigenotype is intact (Mayr 1970). Association with prokaryotic endosymbionts or parasites can result in genome reduction and also an overcomplicated lifecycle including hypermetamorphosis and parthenogenesis. A long co-evolution with Wolbachia Hertig, 1936 is assumed in the case of M. debilis (Grimaldi and Engel 2005; Perkovsky 2012). One of the results is apparently the ���ghost sex life���, linked with a marginalization and vestigialization of the ���ghost adults��� (Perotti et al. 2016). It is likely that the distinctly simplified adult morphology of Micromalthus is closely linked with the obsolete role in the life cycle, and that this applies also to the lesser but already distinct reduction in Archaeomalthus. The apparent stability of morphological simplification in the adult stage suggests a very old origin of a specialized mode of reproduction and possibly an equally old association with endosymbiotic organisms. Selective pressure on mechanical protection and a highly efficient locomotor apparatus in ���ghost adults��� is likely minimal. Apparently, the resulting structural simplifications are irreversible once accomplished, even though the sex-life of adults can be revived as shown by Perotti et al. (2016). In the case of Micromalthidae, the increasing degree of reduction from the Permian to the Miocene is likely a matter of reduced investment in adult structures, and therefore a result of ���evolutionary economy���. A side effect of an association with symbionts can be a reduced ability to survive overheating (Dunbar et al. 2007; Perkovsky 2012). It is likely that the immediate ancestors of extant micromalthid species were also confined to extratropical areas, while the climate of Western Europe in the Ypresian (Early Eocene) was undoubtedly macrothermal, which is confirmed by, among other things, the absence of any Holarctic elements in the amber, in particular, in the myrmecofauna of Oise (Aria et al. 2011; Perkovsky 2016). There are no specific paleoclimatic studies on Babiy Kamen`locality. However, some conclusions about climate during sediment accumulation could be made on the basis of paleofloristic analyses. The Kuznetsk Basin is mostly coal bearing, comprising industrial reserves of hard and brown coal. The process of coal-forming occurred on the former territory of a Carboniferous shallow marine bay, which was replaced by rather swampy lowland plains during the Permian. Alteration of coal and paleosols indicate sediment accumulation in rather humid environments, necessary for the increased accumulation of coal-forming biomass. For the upper part of the section, in which the fossil insects have been found (Dr E. Karasev PIN RAS, 2018 pers. comm. to DV), it is possible to assume alteration of humid and arid climatic conditions. Temperatures were not yet reconstructed for Babiy Kamen`locality. However, significant abundance of conifers (e.g. Quadrocladus, Elatocladus, Voltzia) is reported from the upper part of the Maltsevo Formation (including insect-bearing layers) (Betechtina et al. 1986). It was shown for Permian-Triassic deposits of the Severodvinian Basin that climatic cooling was also characterized by an increased proportion of conifers in Babiy Kamen`locality (Krassilov and Karasev 2009)., Published as part of Evgeny Viktorovich Yana, Rolf Georg Beutel, John Francis Lawrence, Margarita Igorevna Yavorskaya, Thomas H��rnschemeyer, Hans Pohl, Dmitry Vladimirovich Vassilenko, Alexey Semenovich Bashkuev & Alexander Georgievich Ponomarenko, 2019, Archaeomalthus - (Coleoptera, Archostemata) a ' ghost adult ' of Micromalthidae from Upper Permian deposits of Siberia?, pp. 1-9 in Historical Biology 1561672 on pages 5-7, DOI: 10.1080/08912963.2018.1561672, http://zenodo.org/record/2536029, {"references":["Hornschemeyer T, Wedman S, Poinar G. 2010. How long can insect species exist? Evidence from extant and fossil Micromalthus beetles (Insecta: Coleoptera). Zool JLinn Soc. 158: 300 - 311.","Ponomarenko AG. 1969. Historical development of archostematan beetles. 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Evgeny Viktorovich Yana, Rolf Georg Beutel, John Francis Lawrence, Margarita Igorevna Yavorskaya, Thomas Hörnschemeyer, Hans Pohl, Dmitry Vladimirovich Vassilenko, Alexey Semenovich Bashkuev, Alexander Georgievich Ponomarenko (2019): Archaeomalthus -(Coleoptera, Archostemata) a 'ghost adult ' of Micromalthidae from Upper Permian deposits of Siberia? Historical Biology 1561672: 1-9, DOI: 10.1080/08912963.2018.1561672

Genus † Archaeomalthus gen. nov. Type species. Archaeomalthus synoriacos Yan et al., sp. nov., by monotypy. Diagnosis Antennal sockets visible from above; propleuron exposed, narrow, not reaching anterior pronotal margin; procoxae slightly widened, almost contiguous medially; metanotum with metascutum delimited by very distinct longitudinal bulges (alacrista) (Figures 1 (b) and 2(i,k,l)); anterior intercoxal process of metaventrite strongly developed, completely separating mesocoxae. Abdomen with seven visible sternites. Derivation of name Generic name from Greek ‘archaios’ – ‘ancient’ and Micromalthus LeConte, 1878, type genus of family Micromalthidae. Description Body elongated, slender, probably slightly flattened, with distinct shoulder region, slightly rounded laterally posterior to prothorax. Total length ca. 1.18 mm, maximum width at posterior metathoracic region ca. 0.4 mm. Cuticular surface largely smooth on all body regions, without recognizable scales, punctures or tubercles. Head large, as long as pronotum, rectangular, slightly narrower than anterior pronotal margin; with widely separated well-developed compound eyes, inner margins of eyes are finely bordered; ocelli not recognizable, probably absent. Labrum not articulated, apparently fused with clypeus. Concave transverse line present on anterior head capsule, possibly indicating clypeofrontal strengthening ridge. Antennae inserted dorsally but still widely separated, articulatory area close to anteromesal edge of eyes. Mandibles sickle-shaped, with distal halves curved inwards. Maxillae not recognizable. Proximal elements of labium not visible as separate structures, submentum apparently fused with gula and ventral wall of head capsule (Figure 2 (a,b)). Temporal region posterior to eyes very long, more than half as long as the length of head; narrowed neck region absent. Dorsal protuberances missing. Gular plate present, large. Pronotum almost quadrangular, as long as wide, with distinct lateral carina; anterior and posterior angles distinct, triangular; anterior pronotal margin at the same level as the anterior prosternal edge. Prosternal intercoxal process not visible, apparently missing; wide membranous area present posterior to procoxae. Large spiracle recognizable in prothoracic-mesothoracic intersegmental region. Elytral bases distinctly wider than maximum pronotal width; pronoto-elytral angle, i.e. humeral bulges, very distinct, rounded. The shape of elytra roughly quadrangular, with truncated apices. Mesal base enclosed by the semioval scutellar shield. Window punctures and other patterns of surface sculpture absent, degree of sclerotization uniform. Metanotum with distinct longitudinal median groove delimited with strongly developed alacrista; additional longitudinal bulges visible laterally. Mesocoxae widely separated, more or less rounded, nearly triangular, not transverse. Mesocoxal cavities laterally closed by mesepimeron and metanepisternum. Metaventrite large, distinctly narrowed anteriorly, with large triangular, apically rounded anterior intercoxal process; separating mesocoxae completely. Transverse suture of metaventrite not recognizable, probably absent. Metatrochantin not exposed. Metacoxae short, transverse, reaching the lateral edge of ventrite, without recognizable metacoxal plates. Abdomen of parabolic shape, evenly narrowing posteriorly, with rounded apex, as long as meso- and metaventrite combined; at least basal sternites separated by externally visible intersegmental membranes. Four distal abdominal tergites not covered by the elytra. Species included Monotypic. Occurrence Babiy Kamen`locality, Tom`river, Kuznetsk Basin, S. Siberian, in the upper part of the Maltsevo Formation. Remarks Generally, size alone does not justify a placement of a beetle in a specific supraspecific taxon. However, after taking into consideration all the characters mentioned in the Diagonisis and Description, a length of only slightly more than 1 mm should be seen as an additional argument for keeping Archaeomalthus in Micromalthidae. All other archostematan beetles with the exception of the strongly flattened Crowsoniella relicta (Pace 1975) are much larger. The degree of cuticular sclerotization can rarely be adequately estimated on fossil imprints. Therefore, it cannot be used as a solid diagnostic character, even though some surface features such as tubercles, large punctures, etc., can be used for species identification and also in a phylogenetic context (e.g. Beutel et al. 2008; Hörnschemeyer 2009). In the case of Archaeomalthus, the visibility of metathoracic fine details (including metapostnotum) on mostly ventral imprint and elytra (Figure 2 (i,k)), preserved only as faint lines, suggests that Archaeomalthus was overall weakly sclerotized. Elytra of most fossilized beetles, in contrast, are hard structures overlapping the body and usually retaining many structural details (Ponomarenko 1969). Beetle fossils previously known from Babiy Kamen`locality, Petrodromeus Ponomarenko et Volkov, 2013 and Permunda Ponomarenko et Volkov 2013 (Adephaga; Trachypachidae) both have finely preserved elytra with well-defined longitudinal striae (Ponomarenko and Volkov 2013). The abdomen of Archaeomalthus is distinctly shorter than the head and pronotum combined; however, this character is variable in the extant Micromalthus due to varying degrees of extension of the intersegmental membranes. Thus it is not used in the generic diagnosis. The abdominal segments are often more contracted in males than in females, possibly due to different physiological conditions (e.g. development stage of eggs). The length of the abdomen, especially of females, varies in M. debilis Hörnschemeyer et al. 2010.

Genetically modified organisms are crucial for our understanding of gene regulatory networks, physiological processes and ontogeny. With modern molecular genetic techniques allowing the rapid generation of different Drosophila melanogaster mutants, efficient in-depth morphological investigations become an important issue. Anatomical studies can elucidate the role of certain genes in developmental processes and point out which parts of gene regulatory networks are involved in evolutionary changes of morphological structures. The wingless mutation wg

Internal and external features of larvae of Nosodendron fasciculare were examined and compared to character states found in other groups of Derodontoidea and Bostrichoidea. Synapomorphic larval features indicate a sistergroup relationship between Nosodendridae and Derodontidae: tubercular surface structure, body compressed dorsoventrally, tergites with lateral projections, spiracles located on tubular processus. These families share three derived character states with Jacobsoniidae in one of two equally parsimonious trees. However, the monophyletic origin of Nosodendridae + Derodontidae + Jacobsoniidae is not sufficiently established at present. The monophyly of Bostrichoidea (Dermestidae + Bostrichidae + Anobiidae + Ptinidae) is suggested by hypognathism. Larvae of these families are characterized by the absence of the mandibular mola and a robust apical part of the mandible. The monophyly of Bostrichidae + Anobiidae + Ptinidae is indicated by a C-shaped, grub like body and the abdominal apex formed by an enlarged and rounded segment IX. Bostrychiformia are probably paraphyletic. A closer relationship between Bostrichoidea with Cucujiformia is suggested by the possession of cryptonephric malpighian tubules in adults. The specific type of cryptonephridism in Bostrichoidea is probably derived from this condition and is considered autapomorphic. The monophyly of Nosodendridae (Nosodendron) is supported by several autapomorphies. The assignment of the supposed larva of Nosodendron ovatum remains unclear. An inclusion of the dermestid genus Orphilus in Nosodendridae is rejected. Muscular features of larvae of Nosodendron (and Derodontus) are largely plesiomorphic.

The first instar and mature larvae of Altica koreana (Ogloblin) and A. viridicyanea (Baly) are described and illustrated for the first time and compared with larvae of Altica caerulescens (Baly), A. cirsicola Ohno, and A. fragariae (Nakane). A key to the five related Altica species is also given.

Sperm of the dictyopteran key taxon Cryptocercus punctulatus was examined. It has largely maintained a blattodean groundplan condition, with a three-layered acrosome, an elongate nucleus, a single centriole, a conspicuous centriole adjunct material, two connecting bands (=accessory bodies), and a long functional flagellum with a 9+9+2 axoneme provided with accessory tubules with 16 protofilaments and intertubular material. These sperm characters are shared with several other polyneopterans. The sperm of C. punctulatus is very similar to what is found in Periplaneta americana and species of other groups of roaches, including the sperm of Loboptera decipiens described here for the first time. The general sperm organization here described can be assumed for the groundplan of Insecta and Pterygota. The following evolutionary path can be suggested: after the split between Cryptocercidae and the common ancestor of Isoptera, the typical pattern of sperm formation was altered very distinctly, resulting in a duplication or multiplication (Mastotermitidae) of the centrioles. Mastotermes has maintained a certain sperm motility, but with a very unusual apparatus of multiple flagella with a 9+0 axoneme pattern. After the split into Mastotermitidae and the remaining Isoptera, sperm motility was completely abandoned, and different modifications of sperm components occurred, and even the loss of the sperm flagellum.

External and internal structures of the adult head of Glaresis sp. and Dascillus cervinus are described in detail and compared with conditions found in other polyphagan representatives such as Rhipicera sp. and members of Staphyliniformia and Elateroidea. The structures examined do not support a clade Scarabaeoidea + Dascilloidea. No potential synapomorphic features of the head could be identifi ed. In Dascillus a very unusual confi guration of mouthparts is described for the fi rst time, notably the inframandibular antepipharynx. This complex apomorphic feature was also found in members of different groups of Elateroidea s.l., but not in other potentially related lineages. This suggests a possible monophylum ‘Elateroidea s.l. incl. Dascilloidea’. Additional new arguments for such clade are: characteristic scale-like setae on the galea and ligula; a ventrally expanded and bipartite foramen occipitale; a sclerotized tub-shaped prepharyngeal suspensorium; an epipharyngeal surface uniformly covered with microtrichia; similarly shaped mandibles with a concave ventral surface. Characteristics of Dascillus are the presence of a M. verticopharyngalis (plesiomorphic), the presence of two muscles of the posterior hypopharyngeal suspensorium, and bifurcate galeomeres II and ligular lobes. New arguments for a clade ‘Staphyliniformia incl. Scarabaeoidea’ are presented. The most important are the following: presence of a ‘craniobasimaxillary’ muscle; articulation of antennal club segments strongly excentric on outer margin of segments; distal club segment with characteristic sensory pouch; scapus with long bristle- or peg-like setae; ligula separated into a pair of oval shaped and anteriorly setiferous sclerites. Possible autapomorphies of Scarabaeoidea are the following: anterior part of clypeus projecting and covering the labrum; anterior clypeal margin concave and with a transverse row of trichia on its frontal or ventral surface; gula large, rectangular and strongly bulged; inner mandibular edge deeply interrupted by semimembranous lobe. Additionally, a revised terminology of head musculature is newly introduced for Coleoptera.

The adult head of representatives of different adephagan families – aquatic, semiaquatic and terrestrial – were examined and compared. External and internal structures were described and documented in detail for the genera Trachypachus (Trachypachidae), Haliplus (Haliplidae), Amphizoa (Amphizoidae) and the recently discovered Aspidytes (Aspidytidae). A list of characters of potential phylogenetic relevance was compiled and the data matrix combined with the large data set of thoracic and abdominal features for different life stages. The cladistic analysis of this comprehensive data matrix of 138 characters for 16 taxa covering all adephagan families led to one most parsimonous tree. The monophyly of the Geadephaga (Trachypachidae + Carabidae) is strongly supported. The Gyrinidae are the sistergroup of all remaining adephagan beetles. The Meruidae are sister to the Dytiscoidea and both together form the sistergroup of the Haliplidae. The sistergroup relationship of Aspidytidae and Amphizoidae is confirmed. The placement of Meruidae is impeded by the lack of larval characters. It may change when information on structural features of immature stages becomes available. The Trachypachidae, a small relict family with its greatest diversity and distribution in the early Mesozoic, probably come close to the last common ancestor of the Adephaga in the structural features of the adult head. They share structural similarities with the aquatic Dytiscoidea and the terrestrial Carabidae. It is hypothesized that the common ancestor of Adephaga had a relatively unspecialised head morphology and was a predator, possibly with a preference for a riparian habitat. Adaptations for an aquatic environment evolved at least two times and possibly even three times independently. Within these lineages a great diversity of different life styles developed such as the highly specialised surface gliding Gyrinidae, the hygropetric Aspidytidae, the strongly miniaturised Meruidae or the algophagous Haliplidae.

The external and internal cephalic morphology of males and females of Axymyia furcata is described and illustrated in detail. The documented features are compared with those of potentially related groups. Axymyia displays a number of apomorphic features of the adult head, like the subdivision of the compound eyes, the absence of several mucles (M. clypeolabralis, M. stipitopalpalis externus, M. palpopalpalis maxillae primus, Mm. palpopalpalis maxillae primus and secundus), the absence of both maxillary endites, and the loss of the salivary pump musculature (M. hypopharyngosalivarialis). Another apomorphic character is the origin of M. tentorioscapalis anterior on the head capsule. Some features are plesiomorphic and probably belong to the groundplan of Diptera: the orthognathous head, three ocelli, 5-segmented maxillary palps, 2-segmented labial palps transformed into medially fused labella, one premental retractor, a dense vestiture of microtrichia on all exposed parts of the head except the labrum, and the presence of an epipharyngeal food channel. The systematic position of Axymyiidae is discussed. Our findings do not provide support for the phylogenetic position of Axymyiidae.