AbstractTwo specimens of Mobula thurstoni (Lloyd, 1908) were obtained from fishermen of Karangasem, Indonesia, and studied for trypanorhynch cestodes. Archaenybelina gen. nov., including two new species A. pseudotetrabothrialis sp. nov. and A. mimicricestus sp. nov., were recorded from the stomach and spiral valve and analysed for details of scolex and segment morphology, and surface ultrastructure. The new genus is characterized by 4 asymmetrical bothria separated by deep posterior notches, the presence of tegumental grooves, a homeoacanthous heteromorphous armature and a unique segment morphology. Both species can be separated by different hook sizes, basal hook rows and distribution of bothrial microtriches. Scolex surface ultrastructure shows hamulate spinitriches on bothria, lineate spinitriches along bothrial margins, and papilliform filitriches on the scolex peduncle. Similar microtriches have been reported from the bothrial margins of the Tentaculariidae. Tegumental grooves with a probably secretory function based on histology are present on the posterior bothrial margin. A collar of uncinate microtriches appear at the outer surface, separated from an internal bulbous structure, clearly distinguish this organ from the ciliated pits of the Otobothriidae. Based on four bothria, appearing not entirely separated at the anterior part of the scolex that indicates an originally bifossate state, a homeoacanthous heteromorphous armature, tegumental grooves, the absence of prebulbar organs and the presence of muscular rings, we assign the new genus into the Paranybeliniidae Schmidt, 1970. Describing first details of the segment morphology add to the family diagnosis in the most recent classification. The unique morphology of the new genus including its potential life cycle that involves oceanic devil rays as final and euphausiid crustaceans as second intermediate hosts are discussed.

AbstractSperm ultrastructure is frequently employed as a source for phylogenetic inference due to the ease of accessing spermatozoa. Despite being unicellular, sperm cells exhibit a relatively high number of diverse characters and character states. Spermatozoa are subject to strong sexual selection as they are finely tuned for maximizing male reproductive success. Given this strong functional constraint, one might anticipate the emergence of convergent characters in line with similar modes of reproduction. As a result, it might be expected that sperm cells do not possess substantial phylogenetic signal, with functional constraints overshadowing any evolutionary heritage. To test this assumption, we conducted a study on sperm ultrastructure in 11 nemertean species, representing closely related groups and major nemertean lineages. We analyzed these data for their phylogenetic signal within the context of the most recent nemertean phylogenies. Our findings demonstrate that, at all systematic levels, functional constraints imposed by sexual selection, or the mode of reproduction do not supersede the influence of historical constraints on sperm ultrastructure.

AbstractCalceoli are putative sensory organs which are known in limnic, marine, and subterranean amphipods for almost 200 years. Despite an otherwise comprehensive understanding of the sensory organs of crustaceans, we still have not unambiguously understood their function. Since calceoli are mainly found on the antennae of male animals, previous studies suggested a chemosensory function mainly related to reproduction. Here, we use a combination of light and electron microscopic techniques to examine the calceoli of Gammarus locusta (Linnaeus 1758) and Oediceroides calmani (Walker 1906), to provide an overview over these structures, and in addition reveal nervous tissue in close proximity to the calceoli. The calceoli of both species are cuticular structures and consist of proximal and distal elements, a stalk and a receptacle that connects both regions. The two studied calceoli differ in the structure of their proximal and distal element, as well as in their receptacle. This study provides new insight into the functional morphology of the antenna and calceolus. Histological sections through the antennae and the calceoli indicate that the calceoli might possess a mechanosensory function.

AbstractThe tibial organ of Chloropidae and Milichiidae flies is an obscure feature with taxonomic significance. This study provides the first in-depth investigation into the ultrastructure of the hind leg of 11 genera from all Chloropidae subfamilies using a multimodal microscopy approach. The modified dermal tissue associated with the tibial organ indicates glandular function, as evidenced by the presence of secretory vesicles containing non-proteinaceous elements, potentially indicating lipidic secretion. The overall similarity of the tibial organ between Chloropidae and Milichiidae indicates a shared homology. However, the evolutionary history of this structure is still contentious due to limitations in the phylogenetic relationships of both lineages. Moreover, our findings enable future comparative investigations of other Diptera leg organs that possess secretory ability, which could be homologous across schizophoran families, but not necessarily the organs themselves.

AbstractOtophysi is one of the most important fish taxa of the world, as they make up for roughly 28% of all fish species and about two-thirds of all freshwater species worldwide. To understand their success and evolutionary history their sister-group, the Gonorynchiformes, take a key-position, e.g., for reconstructing morphological conditions in the latest common ancestors. Gonorynchiformes comprising only 40 species and have been often studied for that reason. Their pelvic girdle, however, got only little attention so far. Therefore, we studied this structure in extant gonorynchiforms and described the ontogeny in Kneria stappersii. In gonorynchiforms: (1) their basipterygium is principally flat (without dorsal or ventral projections) and placed in horizontal position, (2) has a ‘simple’ shape, i.e., it has only a single anterior process with small cartilaginous tips and becomes wider in its posterior part with a medial portion connecting to the basipterygium of the other side; (3) three radials and a pelvic splint are present, and (4) a prominent posterior process is missing. Although, the morphological situation is a lot similar as seen in clupeiforms and alepocephaliforms. Therefore, these characters have likely been present in the stem of Otomorpha, Ostariophysi, and Otophysi, but within the latter taxon eventually, a higher diversity of pelvic girdle morphology arose during evolution.

AbstractFrostius pernambucensis is a phytotelm-breeding frog with endotrophic larvae. Although the larvae were formally described, no aspect of its internal morphology is known. In this paper, we re-describe the tadpole based on a large sample, describe its internal anatomy (buccopharyngeal cavity and musculo-skeletal system), provide data on natural history, and discuss the evolution of endotrophy and phytotelma colonization. The tadpoles of F. pernambucensis are highly modified, with depressed bodies, reduced mouthparts, and long tails. Many character-states described for these tadpoles can be related to its endotrophic development. Consequence of this highly modified phenotype, we propose several novel putative synapomorphies for the genus: (1) labial tooth row formula 1/1; (2) absence of pustulation in the buccal roof and (3) floor; (4) absence of median ridge; (5) absence of lateral ridge papillae; (6) absence of secretory ridges and pores; (7) absence of filter plates; (7) m. subarcualis rectus II–IV originating on ceratobranchial III; (8) m. subarcualis rectus II–IV inserting on ceratobranchial I; (8) ventral slip of the m. subarcualis rectus I inserting on the ceratobranchial III; (9) suprarostral corpora fused to the cornua trabeculae; (10) commissura quadratoorbitalis absent; (11) cerabranchial II attached to the planum hypobranchiale; and (12) ceratobranchial III attached to the planum hypobranchiale. Finally, we also propose that the presence of a single pair of infralabial papilla could represent a synapomorphy of bufonids. The colonization of phytotelma seem to have created a selective pression on the development of F. pernambucenis, favoring the evolution of endotrophy.

AbstractIn this study, we morphologically examine larval specimens of Ranitomeya variabilis, which were breed in captivity and genetically determined to belong to the French Guiana population. We provide detailed data on the external morphology, chondrocranium, cranial muscle systems and inner organs of the tadpoles. Additionally, we provide essential characteristics for the recognition of the tadpoles of the different Ranitomeya species. The external morphology of the R. variabilis tadpoles was assessed by measurements and photographs of the specimens. Internal morphology was analyzed using µCT images, µCT-based three-dimensional reconstructions, and dissection of specimens for organ and muscle descriptions. The majority of the muscle configurations observed herein for larval specimens of R. variabilis are consistent with data presented in previous studies for larvae of other Ranitomeya species. In addition, several of the observed morphological characters are defined for different taxonomic levels within Dendrobatidae, e.g., the reduction of tectal cartilages and the insertion of the M. rectus cervicis on the third or fourth branchial arch. The absence of the anterolateral process of the ceratohyal in Ranitomeya and Dendrobates further strengthens their close relationship, in contrast to the more distantly related Epipedobates and Phyllobates where this structure is present. The absence of the M. levator arcuum branchialium I and II, the M. interhyoideus posterior and the M. diaphragmatopraecordialis might be defining traits for Ranitomeya. The specific characters observed in this study for R. variabilis, are the fusion of the superficialis and profundus portion of the musculus levator longus larvae and the absence of the parotic crista.

AbstractThe diversity of insects can be explained by their ability to fill various ecological niches, which includes the foraging from diverse sources. The cuticle-based feeding structures interact with the food and show adaptations in shape, material composition and mechanical properties to it. In this study, we focus on the mouthparts of a very prominent ambush predator, the antlion larvae of Euroleon nostras. By nanoindentation, we tested the hardness and the Young’s modulus of the mouthparts, which are significantly harder and stiffer than other insect cuticle structures. To gain insight into the origins of the high values, we studied the degree of tanning using confocal laser scanning microscopy. Additionally, we determined the content of transition and alkaline earth metals by energy dispersive X-ray spectroscopy. We found that the proportions of Zn, Mn, Fe, Cu, Ca, Mg, and Si correlate with the mechanical property values. We also conducted experiments on the breaking stress, the puncturing and biomechanical behaviour of the jaws, which highlighted their extraordinary strength. These findings are not only valuable for biologists, but also for material scientists, as they contribute to our understanding of the origins of mechanical property heterogeneities in insect cuticle.

AbstractProjections from peripheral receptors directly into the protocerebrum of insects have only been little studied. Retrograde staining of nerves from the antennae, maxillary palps and legs has revealed some fibres that project into the central areas of the protocerebrum. In the case of the antennae and palps, it was not known which receptors were responsible for these projections. In the legs of locusts, multipolar neurons (MN) with characteristic terminal dendritic masses (TDM) have been described to project into a neuropil called “superior ventral inferior protocerebrum” (SVIP). However, such neurons have only been found in the abdominal infrared organs of the Australian fire beetle Merimna atrata, where they function as thermoreceptors. In several orthopterans, fibres from the antennae and palps also project into the SVIP. The present work suggests that the multipolar neuron from the infrared organ of Merimna also projects into the protocerebrum, possibly into a ventral region functionally analogous to the SVIP. No MNs but single scolopidia were found in the tips of the antennae and palps of locusts, apparently responsible for projections into the SVIP, where they probably function as receptors for haemolymph pressure.

Dendropsophini is a highly diverse clade with a controversial phylogenetic and taxonomic history. Different generic arrangements have been proposed and the monophyly of several clades supported or rejected. Previous evidence suggested that larval morphology could play an important role in our understanding of the evolution and diversification of Dendropsophini, although data are missing for most lineages, including the sister group of Dendropsophus, Xenohyla. Herein we describe the internal morphology of the tadpoles of X. truncata and compare our results with available information for members of Dendropsophini and closely related lineages. We propose that the presence of a fan-like papilla in the buccopharyngeal cavity, a single element suprarostral, and a triangular process at the base of the muscular process are synapomorphies for Dendropsophini; moreover, the presence of a divided m. subarcualis rectus II–IV seems to be a synapomorphy for Pseudini and, the nasal sac insertion of the m. levator lateralis could be a synapomorphy of Dendropsophini + Pseudini.

Understanding how ecology shapes the evolution of morphological traits is a major goal in organismal biology. By quantifying force of motion, hypotheses on the function of fundamental tasks of animals like feeding can be tested. Ray-finned fishes use various feeding strategies, classified into three main feeding modes: suction, ram and manipulation. While manipulation feeders are usually distinct in morphology and feeding behavior, differentiation between suction and ram feeders is often fine-scaled and transitional. Previous studies have identified different feeding modes and biomechanical adaptations on interspecific and intersexual levels in lake-dwelling sailfin silversides, species of a Sulawesi freshwater radiation. Functional feeding morphology of stream-dwelling species remained in contrast unstudied. We hypothesized that different requirements of riverine habitats favor the evolution of alternative functional adaptations in stream-dwelling sailfin silversides. To test this hypothesis, we investigated feeding of two phenotypically distinct riverine species, Telmatherina bonti and Marosatherina ladigesi, and their sexes, by high-speed videos and biomechanical models. The kinematic approaches identify T. bonti as ram feeder and M. ladigesi as suction feeder. Surprisingly, the biomechanical models of the jaw apparatus provide contradicting results: only one out of three studied parameters varies between both species. Contrarily to lake-dwelling Telmatherina, sexes of both species do not differ in feeding biomechanics. We conclude that T. bonti predominantly uses ram feeding while M. ladigesi primarily uses suction feeding as its main hunting strategy. Feeding biomechanics of stream-dwelling sailfin silversides are less distinct compared to lake-dwelling species, likely due to different trophic ecologies or less stable ecological conditions.

Damselflies and dragonflies are well-known hosts of the West Palaearctic biting midge Forcipomyia paludis. Females of this ectoparasitic dipteran mainly cling to the host’s wings, sucking hemolymph from the wing veins. The midges are firmly attached to the wing surface with specialized tarsi, thus not being flung away during the host’s flight maneuvers. As for another ceratopogonid—F. odonatophila from New Guinea—had been suggested, we assumed that in F. paludis, the attachment would be reinforced by the mouthparts during the suction action. In the present study, we used behavioral field observations, scanning electron microscopy (SEM) and high-resolution micro-computed tomography (µCT), to study the mouthparts of F. paludis. We focused on the mouthpart configuration post sucking and thus on the contact with the host's wing as well as on the piercing process into the wing veins. We foster our understanding of F. paludis being a parasite of Odonata by showing proof of the piercing and therefore the sucking of hemolymph from the wings. Additionally, the mouthparts clearly show contamination with odonate wing wax after the sucking procedure. Furthermore, we discuss probable additional functions of the piercing process for the firm attachment to the flying host of F. paludis.

The female of the biting midge Forcipomyia paludis is a dipteran ectoparasite of West Palaearctic damselflies and dragonflies, sucking haemolymph mainly from wing veins of their hosts. This tiny midge remains firmly attached to the wings even during fast flight and aerial fight maneuvers as shown in the present paper by field studies of the large dragonfly, Cordulegaster boltonii. Since individuals of F. paludis firmly attach themselves to the challenging wing surface of their host and can successfully withstand drag and vibrations during flight, we assume that this midge species has specific microstructural adaptations on its legs for attaching to the wing surface. In our morphological study, we used scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), to study the structure of F. paludis tarsi, as well as the micro morphology of the wing surfaces of their host. Additionally, for the first time, we were able to show attachment devices of the midges dried out in contact with the host’s surface. The spatulae of the plantar setae and especially the empodial setae, are capable of replicating nanoscale wax crystals of the super hydrophobic wing coverage of the dragonfly wing membrane, in order to increase an effective contact area and therefore adhesion. This ability requires extremely soft materials of the spatula, which seems to be rather unique even in comparison to the leg attachment devices of other dipterans and other insect taxa in general.

Phytophagous scarab beetles associated with angiosperms have characteristically enlarged lamellate antennae and exhibit a striking morphological variation of sensilla. In this study, we compared the morphology of antennal surface of 62 species Scarabaeoidea using SEM microscopy, particularly also in light of their evolution in association with angiosperms. We investigated the correlation of antennal sensilla morphology, i.e., their structure and distribution, with species diversity and lineage diversification rates. A high diversity of sensilla was observed but also multiple transitional forms, even on the same antennomere. We interpreted this as evidence for a high evolutionary plasticity. We recognized clear patterns of convergence and repeated evolution of certain types of placoid sensilla. One main tendency found in the phytophagous Pleurostict chafers was a shift from sensilla trichodea to placoid-like sensilla, apparently also enhanced by the increase of the lamellate antennal surface, either by size or number of the lamellae. This trend occurred not only in the Pleurosticts, but also in Glaphyridae, a second angiosperm-associated lineage of Scarabaeoidea. However, our results suggest no direct relation between species diversity or the rate of diversification and general sensilla morphology, i.e., the origin of placoid sensilla. This could be explained not only by species-poor lineages also possessing placoid sensilla but also by otherwise successful and species rich groups having sensilla trichodea (e.g., dung beetles). Results further reveal the need to refine current phylogenetic hypotheses by more comprehensive taxon sampling and to expand the molecular characterization of pheromones and odor binding proteins to better understand the role of chemical communication in scarab diversification.

Within meiofauna, cnidarians are represented by only a few species most of which are in the genus Halammohydra Remane, 1927. It represents highly modified medusae. Information about this group is limited, which complicates its placement in the Cnidarian tree and the relationship to another meiofaunal cnidarian, Otohydra Swedmark & Teissier, 1958. This needs to be clarified with molecular, but also with morphological methods. In this study, the internal organization of H. vermiformis Swedmark & Teissier, 1957 from Sylt and Helgoland (Germany) was examined using transmission electron microscopy (TEM). The ultrastructure of both sexes is documented in this study, i.e. the gastric tube including gonadal compartment, aboral cone, statocysts and tentacles. It is proposed that spermatozoa and oocytes are not released into the water through the gastrodermis, but by rupture of the epidermis, because of structural changes in the epidermis. In both, male and female, there is an indent in the gastric tube and a gap of the mesoglea at the same position. Additionally, we describe the complex structure of the aboral cone with the specialized adhesive organ as well as the accumulation of myofibrils and neurites in the orally directed part of the cone, which indicates high controllability and ability to move in this region.

Developmental plasticity, a common pattern in lissamphibian evolution, results in numerous alternative morphologies among species and also within populations. In the present study, a natural population of the salamander Taricha granulosa (Salamandridae) was examined to detect variation in the vertebral count and to identify potential deformities of their vertebral column. The number of trunk vertebrae varied between 11 and 13 and we recorded 58 individuals with 69 anomalous vertebral elements. These anomalies range from congenital malformations (block vertebrae, unilateral bars, hemivertebrae), extra ossifications in the haemal region, to posttraumatic pathologies. Most osseous pathologies were encountered in the caudal region of the axial skeleton. Our data suggest a high frequency of vertebral malformations in salamanders; however, the identification of the exact causes remains challenging.

New material and new methodologies substantially widen the anatomical knowledge on cocculinid limpets. We first provide 3D-anatomies of Fedikovella caymanensis and Teuthirostria cancellata based on serial sections. Both species differ in several major points (mainly the gill-type and several features of the alimentary tract) from typical cocculinids, accordingly they are classified in a new clade, Teuthirostriidae fam. nov. Specimens studied by McLean and Harasewych (LA County Mus Contrib Sci 453:1–33, 1995) under “Fedikovella beanii” probably represent another species new to science. Additional investigations of original (type) section series of Cocculina laevis Thiele, 1904 (type species of Paracocculina Haszprunar, 1987) and of Cocculina radiata Thiele, 1904 (type species of Coccocrater Haszprunar, 1987) imply some nomenclatorial revisions: Cocculina cervae Fleming, 1948 is designated as type species of Pedococculina gen. nov. Anatomical characters confirm the subsequent placement of Cocculina viminensis Rocchini, 1990 into Coccopigya Marshall, 1986, whereas the original generic status of the whale-fall inhabitant Cocculina craigsmithi McLean, 1992 is confirmed despite the unusual habitat. The latter species probably has symbiotic bacteria in the midgut gland; if so this might be due to the environmental and feeding conditions at whale cadavers or hydrothermal vents. Contrary to Lepetelloidea, the Cocculiniformia cannot be included in Vetigastropoda. Recent molecular data support a sistergroup relationship of Cocculiniformia with Neomphalida, and we add the phenotypic perspective on this so-called “Neomphaliones”-hypothesis. In particular, more phylogenomic data are needed to specify the position of Cocculinida among the rhipidoglossate Gastropoda.

Unfortunately, the captions of figures were incorrectly published in original publication. The corrected version updated here.

We compare the microscopic anatomy of the mouthparts of representative species of Solifugae, Pseudoscorpiones and Parasitiformes (Acari). Specifically, we focus on the epistome, the labrum, the lateral lips (= endites of the pedipalpal coxae) and the musculature of the pharyngeal suction pump. We provide evidence that the labrum is reduced in Solifugae, but present and functional in Pseudoscorpiones and Acari. The epistome constitutes the entire dorsal face of the rostrosoma in Solifugae, but is internalized into the prosoma in Pseudoscorpiones. In Acari, the epistome shows an ancestral morphology, probably close to the ground pattern of chelicerates. The lateral lips of Solifugae contribute to the ventral face of the rostrosoma and the two lips of the mouth opening. In Solifugae, the ventral rostrosoma also includes a sclerite that might derive from a tritosternum. In Pseudoscorpiones, the lateral lips remain independent of the rostrosoma, they interlock ventral to the rostrosoma forming a perioral space. Here, the rostrosoma has an unpaired ventral lip of unresolved morphological origin, which is, however, clearly distinct from the lateral lips of Solifugae. The pharyngeal suction pump differs in all three clades in attachment, number of muscles and origin of muscles. We interpret the data as evidence for independent, parallel evolution of elements of the ground pattern of the (eu)chelicerate mouth parts. Based on the morphological elements of a common euchelicerate ground plan, the rostrosoma evolved independently in the three clades. We reject earlier hypotheses that consider the rostrosoma a character to support a phylogenetic relationship of the three clades.

The accessory neural arch is an oddly distributed character present in several non-acanthomorph teleostean taxa. Its homology was often implied but never satisfyingly tested. In this study, we attended this pending problem. We analyzed the morphology, development, and systematic distribution of the accessory neural arch in teleosts. Using a comprehensive taxon sampling of cleared and stained specimens, we evaluated if the accessory neural arch fulfils existing homology criteria. We then combined these data with recent genetic phylogenies and ancestral character state estimation to reconstruct the evolutionary history of the accessory neural arch. While its gross morphology and development fit homology criteria, results from ancestral character state estimations suggest multiple independent evolutions within teleosts. Although the accessory neural arch cannot be homologous between several teleostean taxa, the concept of parallelism may explain the presence of such a similar character in a variety of non-acanthomorph teleostean taxa.

Phylotranscriptomic studies of the past decade have repeatedly placed Oweniidae together with Magelonidae, as the sister group to remaining annelids. This newly established placement clearly makes them a key-lineage for understanding annelid evolution and morphology. One of the most prominent morphological features of all annelids are their chaetae. The arrangement and formation process (chaetogenesis) of these chitinous bristles have been studied extensively in hooked chaetae that are arranged in rows. However, the information on other types of chaetae is still scarce. In this study, we investigated the scaled capillary notochaetae of Owenia fusiformis, looking both into the formation process that causes the scaly surface ornamentation and into their arrangement within tight bundles. Our results demonstrate the incredible plasticity of chaetogenesis that allows forming a vast array of three-dimensional structures. The capillary chaetae of Owenia fusiformis are unique in lacking an enamel coating and the scales covering the apical surface of each chaeta are formed by a single microvillus of the chaetoblast. Furthermore, the bundle of chaetae has a peripherally located formative site and a central degenerative site and it appears to result from a secondary curling of the chaetal sac.

Mushroom bodies are known from annelids and arthropods and were formerly assumed to argue for a close relationship of these two taxa. Since molecular phylogenies univocally show that both taxa belong to two different clades in the bilaterian tree, similarity must either result from convergent evolution or from transformation of an ancestral mushroom body. Any morphological differences in the ultrastructure and composition of mushroom bodies could thus indicate convergent evolution that results from similar functional constraints. We here study the ultrastructure of the mushroom bodies, the glomerular neuropil, glia-cells and the general anatomy of the nervous system in Sthenelais boa. The neuropil of the mushroom bodies is composed of densely packed, small diameter neurites that lack individual or clusterwise glia enwrapping. Neurites of other regions of the brain are much more prominent, are enwrapped by glia-cell processes and thus can be discriminated from the neuropil of the mushroom bodies. The same applies to the respective neuronal somata. The glomerular neuropil of insects and annelids is a region of higher synaptic activity that result in a spheroid appearance of these structures. However, while these structures are sharply delimited from the surrounding neuropil of the brain by glia enwrapping in insects, this is not the case in Sthenelais boa. Although superficially similar, there are anatomical differences in the arrangement of glia-cells in the mushroom bodies and the glomerular neuropil between insects and annelids. Hence, we suppose that the observed differences rather evolved convergently to solve similar functional constrains than by transforming an ancestral mushroom body design.

Annelids and particularly polychaetes possess a great variety of sensory organs and respond to numerous sensory stimuli. Although eyes and nuchal organs are comparatively well studied, the so-called dorsal organs are among the lesser-known sense organs in aquatic annelids. Moreover, they are known to be restricted to only two out of approximately 80 families of polychaetes—Orbiniidae and Spionidae—which are not closely related. These organs have been regarded as segmentally repeated nuchal organs in the latter taxon, but in Orbiniidae, data are lacking, although it is known that the organs occur almost along the entire trunk except for the anterior-most segments. Furthermore, although the nuchal organ ultrastructure is known to be comparatively uniform for many polychaete species, a comparative investigation has not been conducted in Orbiniidae. To bridge this data gap, we examined an intertidal population of the widely distributed species Scoloplos armiger. Although not completely identical, nuchal and dorsal organs show a high degree of correspondence in the examined specimens. Moreover, both organs correspond to the general structure of nuchal organs. They comprise ciliated supportive cells and bipolar receptor cells and are innervated directly from the brain. The supportive cells form subcuticular spaces and olfactory chambers apically protected by specialized microvilli that house the sensory processes—cilia and microvilli—of the monociliated receptor cells. Therefore, it can be concluded that nuchal and dorsal organs are also identical in Orbiniidae. However, despite general correspondence with spionids, convergent evolution in the two taxa appears to be the most parsimonious interpretation.

The ‘Australian firebeetle’ Merimna atrata approaches fires in Eucalyptus forests for reproduction. Beetles stay on a postfire area as long as burning wood or hot ashes emit heat and smoke. Abdominal infrared receptors protect the beetles from landing on hot spots; however, until now fire-specific adaptations of the antennae have not been investigated in more detail. This affects the localization of olfactory sensilla used for the perception of smoke and in addition mechanisms to protect delicate sensilla against desiccation and pollution. Moreover, nothing was known about antennal thermo-/hygroreceptors in Merimna atrata. We found strong evidence for a functional grouping of the sensilla into receptors used on the ground or in flight, respectively. A first group comprises the outer visible sensilla, i.e. mechanosensory bristles, short gustatory sensilla and a small field of very short olfactory sensilla. They are used when the beetle is running around on the fireground on burnt bark or ashes. A second group of sensilla is hidden in closeable cavities on antennomeres 4–11. If the cavities are closed, the sensilla inside are fully protected. If the cavities are opened in flight, the beetles can make use of many multiporous basiconic sensilla and multiporous basiconic grooved peg sensilla for smoke detection. Minute modified sensilla coelocapitula occurring in small numbers in the cavities too, most probably serve as thermoreceptors. As a result the placing of sensilla deserving protection in closeable cavities and the reduction in number and length of the external sensilla can be interpreted as adaptations to the fire habitat.