Morphology-based Classification Research Articles

Phylogenomics recovers monophyly and early Tertiary diversification of Dipteronia (Sapindaceae)

Dipteronia (Sapindaceae) is an ancient relict woody genus, and contains just two extant species endemic to Southwestern and Central China. As sharing numerous morphological characters, Dipteronia and Acer have long been considered as sister groups forming the traditional family Aceraceae. However, molecular phylogenetics has generally not resolved the phylogenetic placement of Dipteronia, especially not in its expected position as sister to Acer. In this study, we present large-scale, phylogenomic data sets, incorporating complete chloroplast (cp) genome sequences and transcriptome data from 13 Sapindaceae species, to resolve the phylogenetic relationship between Dipteronia and Acer. Moreover, the impact of long-branch attraction (LBA) artefacts and robustness of inferred topologies are assessed by long-branch excluding and coalescent-based methods. Corroborating classical morphology-based classifications, both cp genome and nuclear datasets (2466 co-orthologous genes and 273 co-SCNGs) recover Dipteronia and Acer as mutually monophyletic groups. In addition, our fossil-calibrated molecular phylogenies date the crown of the two extant Dipteronia species to the Paleocene/Eocene boundary, implying that these morphologically highly similar taxa are amongst the oldest ‘living fossils’ of the East Asian Flora.

Evaluation of the genomic diversity of viruses infecting bacteria, archaea and eukaryotes using a common bioinformatic platform: steps towards a unified taxonomy.

Genome Relationship Applied to Virus Taxonomy (GRAViTy) is a genetics-based tool that computes sequence relatedness between viruses. Composite generalized Jaccard (CGJ) distances combine measures of homology between encoded viral genes and similarities in genome organizational features (gene orders and orientations). This scoring framework effectively recapitulates the current, largely morphology and phenotypic-based, family-level classification of eukaryotic viruses. Eukaryotic virus families typically formed monophyletic groups with consistent CGJ distance cut-off dividing between and within family divergence ranges. In the current study, a parallel analysis of prokaryotic virus families revealed quite different sequence relationships, particularly those of tailed phage families (Siphoviridae, Myoviridae and Podoviridae), where members of the same family were generally far more divergent and often not detectably homologous to each other. Analysis of the 20 currently classified prokaryotic virus families indeed split them into 70 separate clusters of tailed phages genetically equivalent to family-level assignments of eukaryotic viruses. It further divided several bacterial (Sphaerolipoviridae, Tectiviridae) and archaeal (Lipothrixviridae) families. We also found that the subfamily-level groupings of tailed phages were generally more consistent with the family assignments of eukaryotic viruses, and this supports ongoing reclassifications, including Spounavirinae and Vi1virus taxa as new virus families. The current study applied a common benchmark with which to compare taxonomies of eukaryotic and prokaryotic viruses. The findings support the planned shift away from traditional morphology-based classifications of prokaryotic viruses towards a genome-based taxonomy. They demonstrate the feasibility of a unified taxonomy of viruses into which the vast body of metagenomic viral sequences may be consistently assigned.

A Proposed Timescale for the Evolution of Armophorean Ciliates: Clevelandellids Diversify More Rapidly Than Metopids.

Members of the class Armophorea occur in microaerophilic and anaerobic habitats, including the digestive tract of invertebrates and vertebrates. Phylogenetic kinships of metopid and clevelandellid armophoreans conflict with traditional morphology-based classifications. To reconcile their relationships and understand their morphological evolution and diversification, we utilized the molecular clock theory as well as information contained in the estimated time trees and morphology of extant taxa. The radiation of the last common ancestor of metopids and clevelandellids very likely occurred during the Paleozoic and crown diversification of the endosymbiotic clevelandellids dates back to the Mesozoic. According to diversification analyses, endosymbiotic clevelandellids have higher net diversification rates than predominantly free-living metopids. Their cladogenic success was very likely associated with sharply isolated ecological niches constituted by their hosts. Conflicts between traditional classifications and molecular phylogenies of metopids and clevelandellids very likely come from processes, leading to further diversification without extinction of ancestral lineages as well as from morphological plesiomorphies incorrectly classified as apomorphies. Our study thus suggests that diversification processes and reconstruction of ancestral morphologies improve the understanding of paraphyly which occurs in groups of organisms with an apparently long evolutionary history and when speciation prevails over extinction.

Increased taxon sampling provides new insights into the phylogeny and evolution of the subclass Calcaronea (Porifera, Calcarea)

Calcaronean sponges are acknowledged to be taxonomically difficult, and generally, molecular data does not support the current morphology-based classification. In addition, molecular markers that have been successfully employed in other sponge taxa (e.g., COI mtDNA) have proven challenging to amplify due to the characteristics of calcarean mitochondrial genomes. A short fragment of the 28S rRNA gene (C-region) was recently proposed as the most phylogenetically informative marker to be used as a DNA barcode for calcareous sponges. In this study, the C-region and a fragment of the 18S rRNA gene were sequenced for a wide range of calcareous taxa, mainly from the subclass Calcaronea. The resulting dataset includes the most comprehensive taxon sampling of Calcaronea to date, and the inclusion of multiple specimens per species allowed us to evaluate the performance of both markers, as barcoding markers. 18S proved to be highly conserved within Calcaronea and does not have sufficient signal to resolve phylogenetic relationships within the subclass. Although the C-region does not exhibit a “proper” barcoding gap, it provides good phylogenetic resolution for calcaronean sponges. The resulting phylogeny supports previous findings that the current classification of the subclass Calcaronea is highly artificial, and with high levels of homoplasy. Furthermore, the close relationship between the order Baerida and the genus Achramorpha suggest that the order Baerida should be abandoned. Although the C-region currently represents the best available marker for phylogenetic and barcoding studies in Calcaronea, it is necessary to develop additional molecular markers to improve the classification within this subclass.

Kinetid structure in sponge choanocytes of Spongillida in the light of evolutionary relationships within Demospongiae

With the advent of molecular phylogenetics, the morphology-based classification of Porifera has been cardinally changed. However, the relationships between some clusters of Demospongiae, the most diverse sponge class, remain uncertain. An analysis of sponge cell ultrastructures, in particular the flagellar apparatus (kinetid) of choano-cytes, may help clarify the evolutionary links in Demospongiae. We studied the kinetid structure of the sponges Spongilla lacustris, Ephydatia fluviatilis and Lubomirskia baikalensis, which belong to the recently established order Spongillida (Heteroscleromorpha). In these sponges, the kinetid of the choanocytes have a uniform structure, consisting of a single kinetosome (without centriole) encircled with a ring of electron-dense bodies producing lateral microtubules. The flagellar transition zone contains a transverse plate with an axosome and a coiled filament. This type of kinetid is similar to that of Haplosclerida representatives, whose morphologic similarities with Spongillida representatives were still not explained. We also discussed the nuclear location in the choanocyte (basal or apical), which correlates to the kinetid structure in Demospongiae. Only three types of flagellar apparatus have been found in Demospongiae up to now, implying that the kinetid is one of the most conservative structures in sponge evolution.

Review of molecular classification and treatment implications of pediatric brain tumors.

Brain tumors are the most common solid tumors and leading cause of cancer-related death in children. The advent of large-scale genomics has resulted in a plethora of profiling studies that have mapped the genetic and epigenetic landscapes of pediatric brain tumors, ringing in a new era of precision diagnostics and targeted therapies. In this review, we highlight the most recent findings, focusing on studies published after 2015, and discuss how new evidence is changing the care of children with brain tumors. Genome-wide and epigenome-wide profiling data have revealed distinct tumor entities within, virtually, all pediatric brain tumor groups including medulloblastoma; ependymoma; high-grade and low-grade gliomas; atypical teratoid/rhabdoid tumors; and other embryonal tumors, previously called CNS primitive neuroectodermal tumors. Whenever integrated with clinical information, many molecular alterations emerge as powerful prognostic markers and should thus be used to stratify patients and tailor therapies. Optimal integration of this newly emerging knowledge in a timely and meaningful way into clinical care is a remarkable task and a matter of active debate. The historical morphology-based classification of tumors is being replaced by a genetic-based classification, and the first generation of molecularly informed clinical trials is underway.

Phylogenomic reclassification of the world\u2019s most venomous spiders (Mygalomorphae, Atracinae), with implications for venom evolution

Here we show that the most venomous spiders in the world are phylogenetically misplaced. Australian atracine spiders (family Hexathelidae), including the notorious Sydney funnel-web spider Atrax robustus, produce venom peptides that can kill people. Intriguingly, eastern Australian mouse spiders (family Actinopodidae) are also medically dangerous, possessing venom peptides strikingly similar to Atrax hexatoxins. Based on the standing morphology-based classification, mouse spiders are hypothesized distant relatives of atracines, having diverged over 200 million years ago. Using sequence-capture phylogenomics, we instead show convincingly that hexathelids are non-monophyletic, and that atracines are sister to actinopodids. Three new mygalomorph lineages are elevated to the family level, and a revised circumscription of Hexathelidae is presented. Re-writing this phylogenetic story has major implications for how we study venom evolution in these spiders, and potentially genuine consequences for antivenom development and bite treatment research. More generally, our research provides a textbook example of the applied importance of modern phylogenomic research.

Measuring genome-wide genetic variation to reassess subspecies classifications in Dodonaea viscosa (Sapindaceae)

Subspecies are traditionally defined on the basis of geographic discontinuities in phenotypic traits, and their circumscription is useful to distinguish morphologically differentiated populations. However, the robustness of morphology-based subspecies classifications in the genomics era is coming under increasing scrutiny, and phylogenies inferred from molecular data may not match with morphological approaches. The division of the shrub Dodonaea viscosa into seven subspecies within Australia has been based mainly on variation in leaf shape, which is a notably variable phenotypic character in this species. So as to assess the alignment between genetic variation and subspecies assignment, we genotyped 67 D. viscosa plants, including representatives from each of the seven subspecies, for 941 single nucleotide polymorphisms. We used network- and Bayesian-based methods to assess genetic relatedness between sampled individuals. Structure analysis identified two genetic clusters, with a further substructure being identified within one of the clusters. Genetic clusters partially aligned with subspecies classifications, particularly for the three most morphologically distinct subspecies (ssp. mucronata, ssp. viscosa and ssp. burmanniana). Subspecies inhabiting the arid zone (ssp. mucronata and ssp. angustissima) exhibited the most distinct genetic clustering. For subspecies inhabiting more temperate regions of its range (ssp. angustifolia, ssp. cuneata and ssp. spatulata), genetic groups did not correspond well with subspecies classifications, but rather were better explained by the geographic origin of individuals. We suggest that the current subspecific classification of the hopbush does not accurately reflect the evolutionary history of this species, and recommend that phenotypic variation be reassessed in light of the genetic structure we describe here. The roles of environmental change, selection and geographic isolation are discussed in an attempt to explain the contemporary distribution of genetic variation in D. viscosa in Australia.

A new genus and species of vespertilionid bat from the Indomalayan Region.

Bats belonging to the subfamily Vespertilioninae are diverse and cosmopolitan, but their systematic arrangement remains a challenge. Previous molecular surveys suggested new and unexpected relationships of some members compared to more traditional, morphology-based classifications, and revealed the existence of taxonomically undefined lineages. We describe here a new genus and species corresponding to an enigmatic lineage that was previously identified within the genus Eptesicus in the Indomalayan Region. Phylogenetic reconstructions based on mitochondrial and nuclear genes relate the new taxon to Tylonycteris and Philetor, and show that specimens associated with this new genus represent 2 genetically distinct species. Although little is known about their ecology, locations of capture and wing morphology suggest that members of this new genus are tree-dwelling, open-space aerial insect predators. The new species has only been documented from Yok Don National Park in Vietnam, so its conservation status is uncertain until more surveying methods target the bat fauna of the dipterocarp forest in Southeast Asia.

Lectins identify distinct populations of coelomocytes in Strongylocentrotus purpuratus.

Coelomocytes represent the immune cells of echinoderms, but detailed knowledge about their roles during immune responses is very limited. One major challenge for studying coelomocyte biology is the lack of reagents to identify and purify distinct populations defined by objective molecular markers rather than by morphology-based classifications that are subjective at times. Glycosylation patterns are known to differ significantly between cell types in vertebrates, and furthermore they can vary depending on the developmental stage and activation states within a given lineage. Thus fluorescently labeled lectins that recognize distinct glycan structures on cell surface proteins are routinely used to identify discrete cell populations in the vertebrate immune system. Here we now employed a panel of fifteen fluorescently-labeled lectins to determine differences in the glycosylation features on the surface of Strongylocentrotus purpuratus coelomocytes by fluorescence microscopy and flow cytometry. Eight of the lectins (succinylated wheat germ agglutinin, Len culinaris lectin, Pisum sativum agglutinin, Saphora japonica agglutinin, Solanum tuberosum lectin, Lycopersicon esculentum lectin, Datura stramonium lectin, Vicia villosa lectin) showed distinct binding patterns to fixed and live cells of three major coelomocyte classes: phagocytic cells, red spherule cells, and vibratile cells. Importantly, almost all lectins bound only to a subgroup of cells within each cell type. Lastly, we established fluorescently-labeled lectin-based fluorescence activated cell sorting as a strategy to purify distinct S. purpuratus coelomocyte (sub-)populations based on molecular markers. We anticipate that this will become a routine approach in future studies focused on dissecting the roles of different coelomocytes in echinoderm immunity.

Critical stresses estimation by crystal viscoplasticity modeling of rate-dependent anisotropy of Al-rich TiAl alloys at high temperature

Determining critical stresses for different slip systems is one of the most important parts in crystal plasticity modeling of anisotropy. However, the task of finding individual critical resolved shear stress (CRSS) for every single slip system, if not impossible, is formidable and a delicate one especially if the microstructure is very complex. Slip family-based, mechanism-based and morphology-based (e.g., phase interface) slip systems classification and hence determining CRSS consistent with experimental measurements are often used in crystal plasticity. In this work, a novel approach to determining CRSS at high homologous temperature has been proposed by crystal plasticity modeling of rate-dependent anisotropy. Two-internal-variable-based phenomenological crystal viscoplasticity model is adopted for simulating isothermal, two-phase, single-crystal-like Al-rich lamellar Ti–61.8at.%Al binary alloy at high-temperature compression state ( $$1050\,^\circ \hbox {C}$$ ) by employing finite strain and finite rotation framework. To the best of authors’ knowledge, this is the first micromechanical modeling attempt with long-period superstructures. Conventional approaches related to CRSS estimation are also compared with the proposed one. Our material parameters are based on calibrating three different sets of compressive stain rate-controlled plasticity data taken from the loading of two different lamellar directions. It is revealed that the proposed approach works fine for rate-dependent anisotropy modeling, while other conventional approaches highly under- or overestimate available anisotropic experimental behavior of this alloy.

New insights in Russula subsect. Rubrinae: phylogeny and the quest for synapomorphic characters

Russula is one of the most speciose genera of mushroom-forming fungi, but phylogenetic relationships among species and subgeneric groupings are poorly understood. Our multi-locus phylogenetic reconstruction places R. firmula, R. rubra, R. rutila and R. veternosa in a well-supported Rubrinae clade, belonging to the Integrae clade of the Crown clade of the genus Russula. Traditional morphology-based classifications placed these four species in two different subsections based on the presence or absence of incrustations on pileocystidia. The Integrae clade also contains R. integra and related species that are traditionally placed in other groups based on their mild taste. Ancestral state reconstruction suggests that the common ancestor of the Crown clade and the Integrae clade probably did not have any incrustations in the pileipellis, had a mild taste, yellow spore print and were associated with angiosperms. All four species of the Rubrinae clade are defined by a darker yellow or ochre spore print, acrid taste and incrustations on pileocystidia. This last character contradicts the former splitting of the group because incrustations were apparently overlooked in R. firmula and R. veternosa. Incrustation type is now highlighted as being important for the delimitation of species and groups within the Crown clade. Pink or red staining of the incrustations in sulphovanillin is present in all species of the Rubrinae clade and a majority of the analysed species of the Integrae clade. The delimitation of the Rubrinae clade and its species circumscriptions are summarised here in a new diagnostic key.

Polycladida phylogeny and evolution: integrating evidence from 28S rDNA and morphology

Polyclad flatworms have a troubled classification history, with two contradicting systems in use. They both rely on a ventral adhesive structure to define the suborders Acotylea and Cotylea, but superfamilies were defined according to eyespot arrangement (Prudhoe’s system) or prostatic vesicle characters (Faubel’s system). Molecular data available cover a very limited part of the known polyclad family diversity and have not allowed testing morphology-based classification systems on Polycladida yet. We thus sampled a suitable marker, partial 28S ribosomal DNA (rDNA), from Polycladida (19 families and 32 genera), generating 136 new sequences and the first comprehensive genetic dataset on polyclads. Our maximum likelihood (ML) analyses recovered Polycladida, but the traditional suborders were not monophyletic, as the supposedly acotyleans Cestoplana and Theama were nested within Cotylea; we suggest that these genera should be included in Cotylea. The partial 28S rDNA trees were generally well supported and robust but in conflict with both Faubel’s and Prudhoe’s superfamilies. Therefore, we compiled morphological and anatomical characters for all taxa used and examined their distribution on our molecular tree. Combining morphological and molecular evidence, we redefined polyclad superfamilies. Acotylea contain tentaculated and atentaculated groups and is now divided in three superfamilies. The suborder Cotylea can be divided in five superfamilies. In general, there is a trait of anteriorization of sensory structures, from the plesiomorphic acotylean body plan to the cotylean gross morphology. Traditionally used characters, such as prostatic vesicle, eyespot distribution, and type of pharynx, are all homoplastic and likely have misled polyclad systematics so far.

An updated classification of rotaliid foraminifera based on ribosomal DNA phylogeny

Abstract Rotaliida is the most diversified order of modern benthic foraminifera, comprising 73 extant families. The current classification of Rotaliida is based exclusively on morphological characters of their calcareous tests. Previous molecular phylogenetic studies partly confirmed morphological classifications but they were based on relatively limited taxon sampling and SSU rRNA gene sequences only. Here, we investigate phylogenetic relationships of rotaliid foraminifera by sequencing complete or partial SSU and LSU rRNA genes for 80 phylotypes representing 70 genera. The analysis of 87 sequences of concatenated genes enabled us to recognize seven rotaliid superfamilies, four of them being established ones (Planorbulinoidea, Discorboidea, Rotalioidea, Nummulitoidea) and three new ones (Glabratelloidea, Calcarinoidea, Serioidea). Although some of these superfamilies were not strongly supported in phylogenetic trees, due to a weak signal of ribosomal genes, they comprise genera and families of distinctive morphological features that have been often united in previous morphology-based classifications. A total of 34 families has been recognized, 10 of them being newly established ones. The placement of three families (Rubratelliidae, Cymbaloporidae, Murrayinelliidae), which occupied isolated branches among the seven superfamilies, could not be determined and they are considered here as incertae sedis. An assemblage of 22 genera representing several morphologically different families of small rotaliids (Clade 3) was not raised to superfamily level because of the lack of molecular and/or morphological support. The phylogenetic relations within this assemblage as well as within the superfamily Rotalioidea have been examined in detail by analyzing partial SSU rDNA sequences for large taxon sampling.

All-passive pixel super-resolution of time-stretch imaging

Based on image encoding in a serial-temporal format, optical time-stretch imaging entails a stringent requirement of state-of-the-art fast data acquisition unit in order to preserve high image resolution at an ultrahigh frame rate — hampering the widespread utilities of such technology. Here, we propose a pixel super-resolution (pixel-SR) technique tailored for time-stretch imaging that preserves pixel resolution at a relaxed sampling rate. It harnesses the subpixel shifts between image frames inherently introduced by asynchronous digital sampling of the continuous time-stretch imaging process. Precise pixel registration is thus accomplished without any active opto-mechanical subpixel-shift control or other additional hardware. Here, we present the experimental pixel-SR image reconstruction pipeline that restores high-resolution time-stretch images of microparticles and biological cells (phytoplankton) at a relaxed sampling rate (≈2–5 GSa/s)—more than four times lower than the originally required readout rate (20 GSa/s) — is thus effective for high-throughput label-free, morphology-based cellular classification down to single-cell precision. Upon integration with the high-throughput image processing technology, this pixel-SR time-stretch imaging technique represents a cost-effective and practical solution for large scale cell-based phenotypic screening in biomedical diagnosis and machine vision for quality control in manufacturing.

Molecular phylogeny of Blaberidae (Dictyoptera, Blattodea) with implications for taxonomy and evolutionary studies

In the present “tree-thinking” period, relying on accurate phylogenetic hypotheses is of paramount importance for biologists interested in an evolutionary perspective. In the Blaberidae cockroaches, a well-defined monophyletic family comprising several model species, no such phylogenetic tree is available despite several earlier contributions. Here, using six molecular markers (12S, 16S, 18S, 28S, COI and COII), we investigate the relationships of Blaberidae and compare our results with the traditional morphology-based classification. This resulted in a broad spectrum of situations, from congruent and well-supported hypotheses (e.g., the monophyly of Blaberidae, Oxyhaloinae and (Geoscapheiinae + Panesthiinae)) to incongruent and weakly supported results (e.g., polyphyly of Perisphaerinae). We emphasize that interesting and contrasted situations lie between the two extremities of this spectrum, especially concerning the genera Thanatophyllum Grandcolas, 1991, Phoetalia Stål, 1874, Laxta Walker, 1868 and Pronauphoeta Shelford, 1909. We also discuss the phylogenetic position of two incertae sedis genera (Eustegasta Gerstaecker, 1883 and Gynopeltis Gerstaecker, 1869). We conclude that in-depth signal analyses should be performed to better understand molecular evolution and its consequence on tree reconstruction for this group. As for phylogenetic relationships per se, new markers should be searched for, especially to decipher deeper relationships in Blaberidae.

Phylogeny of the nominotypical subgenus of Culex (Diptera: Culicidae): insights from analyses of anatomical data into interspecific relationships and species groups in an unresolved tree

The aim of this study was to produce the first objective and comprehensive phylogenetic analysis of the speciose subgenus Culex based on morphological data. We used implied and equally weighted parsimony methods to analyse a dataset comprised of 286 characters of the larval, pupal, and adult stages of 150 species of the subgenus and an outgroup of 17 species. We determined the optimal support by summing the GC supports for each MPC, selecting the cladograms with the highest supports to generate a strict consensus tree. We then collapsed the branches with GC support < 1 to obtain the ‘best’ topography of relationships. The analyses largely failed to resolve relationships among the species and the informal groups in which they are currently placed based on morphological similarities and differences. All analyses, however, support the monophyly of genus Culex. With the exception of the Atriceps Group, the analyses failed to find positive support for any of the informal species groups (monophyly of the Duttoni Group could not be established because only one of the two species of the group was included in the analyses). Since the analyses would seem to include sufficient data for phylogenetic reconstruction, lack of resolution appears to be the result of inadequate or conflicting character data, and perhaps incorrect homology assessments. Molecular and other biological data are needed to gain insights into the evolution of subgenus Culex. Nevertheless, we discuss the placement of several taxa in the current morphology-based classification of the subgenus based on insights realized during the study.

Analysis of Complete Chloroplast Genome Sequences Improves Phylogenetic Resolution in Paris (Melanthiaceae).

The genus Paris in the broad concept is an economically important group in the monocotyledonous family Melanthiaceae (tribe Parideae). The phylogeny of Paris was controversial in previous morphology-based classification and molecular phylogeny. Here, the complete cp genomes of eleven Paris taxa were sequenced, to better understand the evolutionary relationships among these plants and the mutation patterns in their chloroplast (cp) genomes. Comparative analyses indicated that the overall cp genome structure among the Paris taxa is quite similar. The triplication of trnI-CAU was found only in the cp genomes of P. quadrifolia and P. verticillata. Phylogenetic analyses based on the complete cp genomes did not resolve Paris as a monophyletic group, instead providing evidence supporting division of the twelve taxa into two segregate genera: Paris sensu strict and Daiswa. The sister relationship between Daiswa and Trillium was well supported. We recovered two fully supported lineages with divergent distribution in Daiswa; however, none of the previously recognized sections in Daiswa was resolved as monophyletic using plastome data, suggesting that the infrageneric relationships and biogeography of Daiswa species require further investigation. Ten highly divergent DNA regions, suitable for species identification, were detected among the 12 cp genomes. This study is the first successful attempt to provide well-supported evolutionary relationships in Paris based on phylogenomic analyses. The findings highlight the potential of the whole cp genomes for improving resolution in phylogeny as well as species identification in phylogenetically and taxonomically difficult plant genera.

Conflict of mitochondrial phylogeny and morphology-based classification in a pair of freshwater gastropods (Caenogastropoda, Truncatelloidea, Tateidae) from New Caledonia.

Morphological classification and mitochondrial phylogeny of a pair of morphologically defined species of New Caledonian freshwater gastropods, Hemistomia cockerelli and Hemistomia fabrorum, were incongruent. We asked whether these two nominal species can be unambiguously distinguished based on shell morphology or whether the taxonomic discrepancy inferred from these character types was reflected in the variation of shell morphology. Our investigations were based on phylogenetic analyses of a fragment of the mitochondrial cytochrome c oxidase subunit I, geometric morphometric analyses as well as micro computer tomography. The species presorted to morphospecies by eye overlapped in shell shape. However, statistically, all shells were correctly assigned, but not all of them significantly. Qualitatively, both nominal species can be unambiguously distinguished by the presence/absence of a prominent denticle within the shell. In the phylogenetic analyses, individuals from three populations clustered with the “wrong” morphospecies. In the absence of data from multiple loci, it was assumed for the single specimen from one of these populations that its misplacement was due to a recent hybridization event, based on its very shallow position in the tree. For the other two cases of misplacement neither introgression nor incomplete lineage sorting could be ruled out. Further investigations have to show whether the morphological overlap has a genetic basis or is due to phenotypic plasticity. In conclusion, despite their partly unresolved relationships Hemistomia cockerelli and Hemistomia fabrorum may be considered sister species, which are reliably diagnosable by the presence or absence of the denticle, but have not yet fully differentiated in all character complexes investigated.

A New Morphological Phylogeny of the Ophiuroidea (Echinodermata) Accords with Molecular Evidence and Renders Microfossils Accessible for Cladistics.

Ophiuroid systematics is currently in a state of upheaval, with recent molecular estimates fundamentally clashing with traditional, morphology-based classifications. Here, we attempt a long overdue recast of a morphological phylogeny estimate of the Ophiuroidea taking into account latest insights on microstructural features of the arm skeleton. Our final estimate is based on a total of 45 ingroup taxa, including 41 recent species covering the full range of extant ophiuroid higher taxon diversity and 4 fossil species known from exceptionally preserved material, and the Lower Carboniferous Aganaster gregarius as the outgroup. A total of 130 characters were scored directly on specimens. The tree resulting from the Bayesian inference analysis of the full data matrix is reasonably well resolved and well supported, and refutes all previous classifications, with most traditional families discredited as poly- or paraphyletic. In contrast, our tree agrees remarkably well with the latest molecular estimate, thus paving the way towards an integrated new classification of the Ophiuroidea. Among the characters which were qualitatively found to accord best with our tree topology, we selected a list of potential synapomorphies for future formal clade definitions. Furthermore, an analysis with 13 of the ingroup taxa reduced to the lateral arm plate characters produced a tree which was essentially similar to the full dataset tree. This suggests that dissociated lateral arm plates can be analysed in combination with fully known taxa and thus effectively unlocks the extensive record of fossil lateral arm plates for phylogenetic estimates. Finally, the age and position within our tree implies that the ophiuroid crown-group had started to diversify by the Early Triassic.