Environment-specific shell shape variation in the boring mytilid Leiosolenus patagonicus

Environmental conditions induce phenotypic responses (behavioural, morphological and physiological) in many marine species. The boring mytilid Leiosolenus patagonicus inhabits different types of substrata, such as sandstone intertidal and hard subtidal substrata (here called ‘lifeless-substratum’) and shells of bivalve species (here called ‘live-substratum’), where they are exposed to different restrictions in their growth. We used geometric morphometric methods to compare the contour shell shapes from each type of substratum (live and lifeless) since we expected the body shape to differ between individuals from these different substrata. The results showed that the shell shape depends on the type of substratum where the larvae recruit. The mean shell shapes of individuals from the live-substratum are more slender than those of the individuals growing inside the lifeless-substratum. Individuals from live-substratum can adapt their phenotype depending on the oyster’s anti-parasitism responses, while in lifeless-substratum they are able to build their own refuges.     

Evolutionary relationships of euthyneuran gastropods (Mollusca): a cladistic re-evaluation of morphological characters

Morphological characters of the Euthyneura available from the literature were re-evaluated in terms of terminology and primary homology. A total of 77 characters and 75 taxa were retained in a data matrix. Several assumptions on character weights and types were tested. In the cladistic analyses, it appeared that the data matrix was highly homoplastic, and only robust nodes (those which were little modified by variations in weight and coding of characters) were retained in a concensus tree. The evolutionary histories of all characters and monophylies of higher euthyneuran taxa were discussed. The following interrelationships of the taxa were obtained in a consensus tree: the clade Heterobranchia includes paraphyletic allogastropod taxa which emerge basally, and the clade Euthyneura. The latter includes the clade Pulmonata and at least 10 opisthobranch clades of unresolved relationship (Thecosomata, Gymnosomata, Acochlidioidea, Pyramidelloidea, Runcinoidea, Cephalaspidea, Sacoglossa, Umbraculoidea, Pleurobranchoidea, Nudibranchia). The Pulmonata include basommatophoran paraphyletic taxa and the clade Geophila (Onchidiidae, Soleolifera, Stylommatophora). The position of the Sacoglossa and the monophyly of the Notaspidea are also discussed.  © 2002 The Linnean Society of London, Zoological Journal of the Linnean Society , 2002, 135 , 403–470.     

Identification of ecophenotypic trends within three European freshwater mussel species (Bivalvia: Unionoida) using traditional and modern morphometric techniques

Most species of freshwater mussels (Unionoida) show a wide variability in shell form and size but an understanding of which factors determine unionoid morphology is poor. We identified ecophenotypic trends in shell and internal characters within three unionoid species from two habitat types (marinas and river) of the River Thames, UK, using traditional and modern morphometric techniques. In marinas, all species grew to larger maximum sizes than in the river, which might be a result of higher temperatures and phytoplankton densities in marinas. Unio pictorum in marinas was more elongated than in the river and Fourier shape analysis revealed a trend from dorsally arched river specimens to straight dorsal and pointed posterior margins in marina individuals. The degree of shell elongation and shape of dorso‐posterior margin were not associated with sediment composition, but were associated with the different hydrological characters of the two habitat types. Relative shell width was a poor indicator of collection site and influenced by allometric growth. Unlike U. pictorum, a difference in shell elongation of marina and river mussels could not be detected in Unio tumidus and Anodonta anatina. However, all three species showed the same trends regarding the shape of the dorso‐posterior shell margin. This shell character may thus have broad ecological significance and could have considerable utility to palaeontologists, taxonomists, and conservation biologists. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 814–825.     

Potential key characters in Opisthobranchia (Gastropoda, Mollusca) enhancing adaptive radiation

Five potential key characters which might have enhanced species radiation in the Opisthobranchia (Gastropoda) are discussed. These are: 3–4 cuticular plates in the gizzard of Cephalaspidea s.str., kleptoplasty in Sacoglossa, kleptocnides in Aeolidoidea, a symbiotic relationship with unicellular algae in Phyllodesmium Ehrenberg, 1831, and mantle dermal formations in Chromodorididae. Interpretation of the characters as key innovations is based on phylogeny and/or comparison of species numbers in subgroups. Possible adaptive zones are discussed, and alternative interpretations indicated.     

A multivariate study of geographic variation in the whelk Dicathais

An analysis has been made of the variation in shell shape and shell characteristics of 889 Australian and New Zealand specimens of the genus Dicathais, using multivariate techniques. Shell measurements taken were: the overall length, length of spire, length of aperture, and width of aperture. Weight of the shell plus the preserved animal was also recorded. The sculpture of the shell, thickness of the lip, and the presence or absence of a reddish or purplish colouration or banding on the inside of the lip, were assessed qualitatively.Principal component analyses of the size measurements for each site showed that the first principal component, which accounted for greater than 95% of the variation at each site, was associated with variation in the ‘size’ of the animal. Canonical analysis of the size measurements showed a cline in shell shape from the animals on the western side of Australia to those on the eastern side of Australia and New Zealand. The resulting canonical variates were associated with variation in the ‘shape’ of the shell. Principal component analyses of the between-group matrix and of the within-group matrix of the size measurements showed that the site means exhibited a similar pattern of dispersion to that of the animals within each site.Canonical analysis of the shell characteristics showed that variation along the first canonical axis was largely produced by shell sculpture, while variation along the second resulted from differences in colouration/banding.The generalized variances of the correlation matrices for the size measurements showed that groups with similar shell shape were associated with the presence of granite substrata and/or mussel beds or, alternatively, with limestone substrata, but canonical correlation analysis of the relationship between the size measurements and shell characteristics showed that no consistent trend was evident over all sites.A subjective examination of the structure of the radula of 84 animals showed that two distinct morphological forms were present, but that they were not correlated either with sex or any of the named shell forms or site groupings.An analysis of the growth curves of 27 animals of the two forms from the eastern and western coasts of Australia, held in the laboratory, was carried out. The eastern coast form showed a loss of sculpturing and a change in shell shape when kept under west coast conditions and on a mussel diet.Water temperature, diet, substratum, and degree of exposure to wave action were all found to show associations with variations in either shell shape or shell characteristics. It is suggested that the selective force of the habitat which produces changes in shell shape and shell characteristics of the animals at any site is a complex of factors, many of which are interrelated. The genetic basis for the development of shell shape and production of the shell characteristics in Dicathais may be similar to that found in Nucella lapillus (L.) in the Northern Hemisphere.These data suggest that the Dicathais found at the sites studied in this investigation are all part of the same ‘population’, the shell shape and shell characteristics of the adult populations being determined both by selection and phenotypic expressions caused by the selective force of the habitat at each site. It is concluded that the genus consists of a single highly variable species.The value of the application of multivariate analyses to this type of study is shown to lie in the way in which the techniques provide an overall picture of the variation within sites and of the variation between sites.     

The evolution of egg shape in birds: selection during the incubation period

A recent broad comparative study suggested that factors during egg formation – in particular ‘flight efficiency’, which explained only 4% of the interspecific variation – are the main forces of selection on the evolution of egg shape in birds. As an alternative, we tested whether selection during the incubation period might also influence egg shape in two taxa with a wide range of egg shapes, the alcids (Alcidae) and the penguins (Spheniscidae). To do this, we analysed data from 30 species of these two distantly related but ecologically similar bird families with egg shapes ranging from nearly spherical to the most pyriform eggs found in birds. The shape of pyriform eggs, in particular, has previously proven difficult to quantify. Using three egg‐shape indices – pointedness, polar‐asymmetry and elongation – that accurately describe the shapes of all birds’ eggs, we examined the effects of egg size, chick developmental mode, clutch size and incubation site on egg shape. Linear models that include only these factors explained 70–85% of the variation in these egg‐shape indices, with incubation site consistently explaining > 60% of the variation in shape. The five species of alcids and penguins that produce the most pyriform eggs all incubate in an upright posture on flat or sloping substrates, whereas species that incubate in a cup nest have more spherical eggs. We suggest that breeding sites and incubation posture influence the ability of parents to manipulate egg position, and thus selection acting during incubation may influence egg‐shape variation across birds as a whole.     

External morphology of the male of Cyclestheria hislopi (Baird, 1859) (Crustacea, Branchiopoda, Spinicaudata), with a comparison of male claspers among the Conchostraca and Cladocera and its bearing on phylogeny of the 'bivalved' Branchiopoda

The adult male of Cyclestheria hislopi, sole member of the spinicaudate conchostracan clam shrimp family Cyclestheriidae and a species of potential phylogenetic importance, is described for the first time. Several previously unknown features are revealed. Among these are (1) the morphology of the dorsal organ, which is roughly similar in shape to the supposedly homologous structure in other clam shrimps but bears a relatively large, centrally located pore unique to the species; (2) an anterior cuticular pore presumably leading to the ‘internal’ space surrounding the compound eyes, and thereby homologous to the same pore in other clam shrimps and in the Notostraca; (3) the spination and setation of the antennae and thoracopods, and (4) the mature male first thoracopods (claspers). The male claspers are paired and essentially equal in size and shape on right and left sides of the body. The second pair of thoracopods are not modified as claspers, a situation different from all other spinicaudate families but shared (plesiomorphic we propose) with the laevicaudatans and most cladocerans. The claspers bear a field of special spine-like setae on the extremity of the ‘palm’; this setal type, previously unrecognized, is unique to Cyclestheria. The palm of the clasper also bears two palps (one very small), as in other conchostracan species (both laevicaudatans and spinicaudatans). The movable finger of the clasper, modified from the thoracopod endopod, bears a row of long setae along its outer extremity, also unique. Cyclestheria exhibits a mixture of characters, some unique and others typical of the Spinicaudata (Conchostraca). Cladoceran clasper types are briefly reviewed. as are the claspers in the Spinicaudata and Laevicaudata (Conchostraca). Morphology of the clasper of Cyclestheria shows typical spinicaudate characters. It is suggested that claspers on the first thoracopods may be a synapomorphy for the Conchostraca and the Cladocera. The possible role of Cyclestheria or a Cyclestheria-like ancestor in cladoceran phylogeny is briefly discussed in light of recent suggestions (Martin and Cash-Clark, 1995) of cladoceran monophyly and possible ancestral relationships with this genus. Some possibilities concerning the phylogenetic position of Cyclestheria–either as a sister group to the rest of the Spinicaudata or as a sister group to the Cladocera—are discussed.     

Phylogenetic patterns of mimicry strategies in Darnini (Hemiptera: Membracidae)

A phylogenetic analysis based on 58 morphological characters including 18 species representing 14 genera over the 15 currently known in Darnini (Hemiptera: Membracidae) confirms the monophyly of this tribe. This result is particularly supported by the presence of cucullate setae on the ventral side of the femora. Two sister clades are inferred: the clade Funkhouseriana+ which groups four genera (Aspona, Cyphotes, Funkhouseriana, Taunaya) and exhibits a ‘bird dropping’ habitus and all other genera which exhibit a ‘dewdrop’ like habitus (Alobia, Darnis, Dectonura, Hebetica, Hebeticoides, Leptosticta, Ochrolomia, Stictopelta) or a ‘thorny’ habitus (Alcmeone, Sundarion). In the ‘dewdrop’ habitus, only the clade Ochrolomia+ is retained as a monophyletic unit. According to these results, pronotal shapes and habitus have evolved independently in each monophyletic unit and each one seems correlated with a particular type of mimicry strategy. According to the strategy, characters involved are different, a priori independent; moreover, they look coordinated regarding to the mimicry function they serve. The various evolutionary scenarios are discussed in relation to the phylogeny, and particularly in correlation with the non-gregarious behavior of these membracids, also coherent with their mimicry strategy.     

Spermatozoa of tapeworms (Platyhelminthes,Eucestoda): advances in ultrastructural and phylogenetic studies

New data on spermiogenesis and the ultrastructure of spermatozoa of ‘true’ tapeworms (Eucestoda) are summarized. Since 2001, more than 50 species belonging to most orders of the Eucestoda have been studied or reinvestigated, particularly members of the Caryophyllidea, Spathebothriidea, Diphyllobothriidea, Bothriocephalidea, Trypanorhyncha, Tetraphyllidea, Proteocephalidea, and Cyclophyllidea. A new classification of spermatozoa of eucestodes into seven basic types is proposed and a key to their identification is given. For the first time, a phylogenetic tree inferred from spermatological characters is provided. New information obtained in the last decade has made it possible to fill numerous gaps in the character data matrix, enabling us to carry out a more reliable analysis of the evolution of ultrastructural characters of sperm and spermiogenesis in eucestodes. The tree is broadly congruent with those based on morphological and molecular data, indicating that convergent evolution of sperm characters in cestodes may not be as common as in other invertebrate taxa. The main gaps in the current knowledge of spermatological characters are mapped and topics for future research are outlined, with special emphasis on those characters that might provide additional information about the evolution of tapeworms and their spermatozoa. Future studies should be focused on representatives of those major groups (families and orders) in which molecular data indicate paraphyly or polyphyly (e.g. ‘Tetraphyllidea’ and Trypanorhyncha) and on those that have a key phylogenetic position among eucestodes (e.g. Diphyllidea, ‘Tetraphyllidea’, Lecanicephalidea, Nippotaeniidea).     

COI barcoding of Nebelid testate amoebae (Amoebozoa: Arcellinida): extensive cryptic diversity and redefinition of the Hyalospheniidae Schultze

We used Cytochrome Oxidase Subunit 1 (COI) to assess the phylogenetic relationships and taxonomy of Nebela sensu stricto and similar taxa (Nebela group, Arcellinida) in order to clarify the taxonomic validity of morphological characters. The COI data not only successfully separated all studied morphospecies but also revealed the existence of several potential cryptic species. The taxonomic implications of the results are: (1) Genus Nebela is paraphyletic and will need to be split into at least two monophyletic assemblages when taxon sampling is further expanded. (2) Genus Quadrulella, one of the few arcellinid genera building its shell from self-secreted siliceous elements, and the mixotrophic Hyalosphenia papilio branch within the Nebela group in agreement with the general morphology of their shell and the presence of an organic rim around the aperture (synapomorphy for Hyalospheniidae). We thus synonymise Hyalospheniidae and Nebelidae. Hyalospheniidae takes precedence and now includes Hyalosphenia, Quadrulella (previously in the Lesquereusiidae) and all Nebelidae with the exception of Argynnia and Physochila. Leptochlamys is Arcellinida incertae sedis. We describe a new genus Padaungiella Lara et Todorov and a new species Nebela meisterfeldi n. sp. Heger et Mitchell and revise the taxonomic position (and rank) of several taxa. These results show that the traditional morphology-based taxonomy underestimates the diversity within the Nebela group, and that phylogenetic relationships are best inferred from shell shape rather than from the material used to build the shell.     

Towards a phylogeny of gastropod molluscs: an analysis using morphological characters

Morphological (including ultrastructural) and developmental characters utilized in recent literature are critically reviewed as the basis to reassess the phylogenetic relationships of gastropods. The purpose of this paper is to provide a framework of characters for future studies and a testable phylogenetic hypothesis. This is one of the first attempts to use such characters to assess the relationships of all major clades using parsimony methods. The analysis uses 117 characters and includes 40 taxa, predominantly ‘prosobranchs’. Five outgroup taxa are included, representing four conchiferan groups and Poly-placophora. Of the 117 characters reviewed and included in the analyses, nine are shell characters (four of these are shell structure), two opercular, two muscular, four ctenidial, 12 renopericardial and 24 reproductive (including 17 based on sperm and spermatogenesis), 27 of the digestive system, 32 of the nervous system and sense organs; the remainder are developmental (3) and of the foot and hypobranchial gland. In the initial analysis the data set included a mixture of binary and multistate characters with all characters unordered. These data were also analysed after scaling so that each character had equal weight. A third data set was constructed in which all characters were coded as binary characters. These analyses resulted in some implausible character transformations, mainly-involving the regaining of lost pallial structures. Additional analyses were run on all three sets of data after removing five characters showing the most unlikely transformations. These analyses resulted in generally similar topologies. The robustness of the clades was tested using clade decay. The adaptive radiation of gastropods and their life history traits are briefly described and discussed and the terminology for simultaneous hermaphroditism refined. A scenario for the evolution of torsion equated with the fossil record is proposed and the effects of torsion and coiling on gastropods are discussed along with asymmetry imposed by limpet-shaped body forms. It is suggested that the first gastropods were ultradextral. The idea that heterochrony has played a major part in gastropod evolution is developed and discussed, particularly the paedomorphic stamp imposed on the apogastropods. The veliger larvae of caenogastropods and heterobranchs are contrasted and found to differ in many respects. The evolution of planktotrophy within gastropods is discussed. Recent phylogenetic hypotheses for gastropods based on molecular data are generally in broad agreement with the present results. On the basis of our analyses we discuss the major monophyletic groups within gastropods. Gastropods appear to be a monophyletic clade, and divide into two primary groups, the Eogastropoda (incorporating the patellogastropods and their (probably sinistrally coiled) ancestors and the Orthogastropoda – the remainder of the gastropods. Orthogastropoda comprises several well defined clades. The vetigastropod clade encompasses most of the groups previously included in the paraphyletic Archaeogastropoda (fissurellids, trochoideans, scissurelloideans, halioroideans pleurotomarioideans) as well as lepeto-driloidean and lepetelloidean limpets and seguenzids. The location of the hot vent taxa Peltospiridae and Neomphalidae varies with each analysis, probably because there is a lack of ultrastructural data for these taxa and parallelism in many characters. They either form a paraphyletic or monophyletic group at or near the base of the vetigastropods or a clade with the neritopsines and cocculinoideans. The neritopsines (Neritoidea etc.) consistently form a clade with the cocculinoidean limpets, but their position on the tree also differs depending on the data set used and (in the case of the scaled data) whether or not the full suite of characters is used. They are either the sister to the rest of the orthogastropods or to the apogastropods. Caenogastropods [Mesogastropoda (+ architaenioglossan groups) + Neogastropoda] are consistently monophyletic as are the heterobranchs (‘Heterostropha’+ Opisthobranchia + Pulmo-nata). The caenogastropods and heterobranchs also form a clade in all the analyses and the name Apogastropoda is redefined to encompass this group. New taxa are proposed, Sorbeoconcha for the caenogastropods exclusive of the architaenioglossan taxa, and Hypsogastropoda for the ‘higher caenogastropods“– the Sorbeoconcha exclusive of the Cerithioidea and Campaniloidea.     

Spatial patterns of disparity and diversity of the Recent cuttlefishes (Cephalopoda) across the Old World

Aim Diversity and disparity metrics of all Recent cuttlefishes are studied at the macroevolutionary scale (1) to establish the geographical biodiversity patterns of these cephalopods at the species level and (2) to explore the relationships between these two metrics. Location Sampling uses what is known about these tropical, subtropical and warm temperate cephalopods of the Old World based on a literature review and on measurements of museum specimens. Some 111 species spread across seventeen biogeographical areas serve as basic units for exploring diversity and disparity metrics in space. Methods Landmarks describe the shape of the cuttlebone (the inner shell of the sepiids) and differences between shapes are quantified using relative warp analyses. Relative warps are thus used as the morphological axis for constructing morphospaces whose characteristics are described by disparity indices: total variance, range, and minimum and maximum of relative warps. These are analysed and then compared with the diversity (species richness) metric. Results Results show no significant latitudinal or longitudinal gradients either for diversity or for disparity. Around the coast of southern Africa, disparity is high regardless of whether diversity (species richness) is high or low. In the ‘East Indies’ area disparity is low despite the high diversity. Main conclusions The relationship between diversity and disparity is clearly not linear and no simple adjustment models seem to fit. The number of species in a given area does not predict its disparity level. The particular pattern of southern Africa may be the result of paleogeographical changes since the Eocene, whereas that of the ‘East Indies’ may indicate that this area could act as a centre of origin. However, the lack of any clear phylogenetical hypothesis precludes the study from providing any explanation of the observed patterns.     

When rare species become endangered: cryptic speciation in myrmecophilous hoverflies

The myrmecophilous hoverfly, Microdon mutabilis, is listed as a ‘Rare’ or ‘Nationally Notable Species’ in UK Red Data Books. As an obligate social parasite, feeding only from ant colonies, its life‐style satisfies theoretical conditions under which cryptic speciation is predicted to evolve; namely, strong selection for nonmorphological adaptations that enhance its exploitation of a local subspecies or populations of its host. Samples of larvae and pupae in Ireland, Scotland and England showed that M. mutabilis exploits a single and different host ant species on different sites across its range. In nine southern English colonies, 95.6% of infested nests were of Myrmica scabrinodis whereas in six Irish and two Scottish colonies 100% and 94.2%, respectively, of the infested nests were of Formica lemani, despite M. scabrinodis being common at all sites. Although the adults from ‘scabrinodis’ (and lemani) populations are cryptic, morphometric measurements of pupae showed consistent diagnostic characters that were sufficiently distinct for these ecotypes to be classed as separate species. We conclude that M. mutabilis is the ‘lemani‐type’ and designate the ‘scabrinodis‐type’ as a new species, Microdon myrmicae spec. nov. Thus, one of the listed threatened species of the British Isles becomes two species, each possessing about half the number of populations and occupying half the range of the original ‘species’. Each also inhabits a different serai stage within grassland or heathland, and will require a different management regime if its declining populations are to be conserved. ‘M. mutabilis’ is reported with other host ant species on the European continent. In the light of our results, these may prove to be additional cryptic species. We suggest that cryptic speciation is apt to evolve in species, such as myrmecophiles, endoparasites and koinobiont parasitoids, whose life‐styles result in strong selection on their physiological or behavioural characters. The implications for Red Data Book classifications and for practical conservation are discussed. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 75 , 291–300.     

The pretarsus in Chalcidoidea (Hymenoptera Parasitica): functional morphology and possible phylogenetic implications

The structure of the pretarsus of chalcid wasps (Hymenoptera: Chalcidoidea) was examined with light and scanning electron microscopy. The pretarsus of these wasps is characterized by a distal elastic widening of the planta that spreads over the arcus, by a pair of folding plates at the dorsal side of the arolium (the dorsal plates), and by the absence of auxiliary sclerites. The surface of the fully spread arolium of chalcids has a spongiform structure. The arcus of chalcids is an apodeme of the planta. The peculiarities of the inverting/everting biomechanics of the pretarsus of chalcids involve: 1) interactions between the elastic part of the planta, the dorsal plates and the manubrium, and 2) the functioning of the elastic part of the planta and the arcus together as a single unit. A single apical seta situated distally from the campaniform sensillae and proximal row of setae on the manubrium are regarded as putative synapomorphies of Chalcidoidea. A manubrium with a distinct proximal row of three setae characterizes almost all Eulophidae, Aphelinidae and Signiphoridae (‘eulophid lineage’) and Tetracampidae, whereas a row of two setae characterizes Mymaridae, Rotoitidae and Trichogrammatidae. Other studied families (Pteromalidae, Eurytomidae, Torymidae, Ormyridae, Eupelmidae, Encyrtidae, Perilampidae), which represent a ‘pteromalid lineage’, are characterized mostly by five setae in a proximal row, which could represent a synapomorphy for these groups, or a symplesiomorphy in Chalcidoidea, depending on rooting. However, the characters may be correlated with differences in body size that characterize the different lineages rather than being phylogenetically important. Other characters that may be phylogenetically informative are: 1) shape of the manubrium (spindle‐like in Mymaridae, Rotoitidae, Trichogrammatidae and the ‘eulophid lineage’, but mostly bottle‐like in representatives of the ‘pteromalid lineage’), and 2) pubescence of the proximal part of the planta (sparse, thick setae in Rotoitidae, Trichogrammatidae and the ‘eulophid lineage’, but dense, slender setae in representatives of the ‘pteromalid lineage’).     

The phylogenetic position of the Clitellata and the Echiura - on the problematic assessment of absent characters*

Absent characters (negative characters) are difficult to assess and their correct interpretation as symplesiomorphies, synapomorphies or convergencies (homoplasies) is one of the greatest challenges in phylogenetic systematics. Different phylogenetic assessments often result in contradictory phylogenetic hypotheses, in which the direction of evolutionary changes is diametrically opposed. Especially in deciding between primary (plesiomorphic) and secondary (apomorphic) absence, false conclusions may be reached if only the outgroup comparison and the principle of parsimony are employed without attempting any biological evaluation or interpretation of characters. For example, in the higher‐level systematization of the Annelida and related taxa different assessments of absent characters have led to conflicting hypotheses about the phylogenetic relationships and the ground pattern of the annelid stem species. Varying phylogenetic interpretations regarding the absence of the chemosensory nuchal organs in the clitellates and their presence in polychaetes initiated a controversy that produced two alternative phylogenetic hypotheses: (1) the Clitellata are highly derived Annelida related to a subtaxon within the, in this case, paraphyletic ‘Polychaeta’ or (2) the Clitellata are comparatively primitive Annelida representing the sister group of a monophyletic taxon Polychaeta. In the former, the absence of nuchal organs in the Clitellata is regarded as a secondary character, in the latter as primary. As most Clitellata are either limnetic or terrestrial, we must ask which characters are plesiomorphies, taken from their marine stem species without changes. In addition to a thorough investigation and evaluation of clitellate characters, a promising approach to these questions is to look for such characters in limnetic and terrestrial annelids clearly not belonging to the Clitellata. A similar problem applies to the evaluation of the position of the Echiura, which lack both segmentation and nuchal organs. Evidence is presented that in both taxa these absent characters represent derived, apomorphic character states. The consequences for their phylogenetic position and the questionable monophyly of the Polychaeta are discussed. The conclusion drawn from morphological character assessments is in accordance with recently published hypotheses based on molecular data.     

Miniatures,morphology and molecules: Paedocypris and its phylogenetic position (Teleostei,Cypriniformes)

We review the morphological and molecular evidence that Mayden & Chen recently used to infer that the developmentally truncated fish genus Paedocypris is not a member of the teleost order Cypriniformes or carp‐like fishes, but is ‘the basal sister group to all Cypriniformes’. This hypothesis contradicts several previous studies that used molecular sequence data or morphological characters. A review of the morphological characters that Mayden & Chen discussed and mapped onto their ‘simplified tree’ shows that these, analysed alone, rather support a close relationship of the cyprinids Sundadanio, Danionella, and Paedocypris. We also present four additional analyses of morphological data, which all contradict Mayden & Chen's result. Despite its highly reductive skeleton, posing a serious problem when analysing its phylogenetic position with skeletal characters, the presence in Paedocypris of the basioccipital masticatory plate is compelling evidence that it is a member of the Cyprinoidei (Cyprinidae plus Psilorhynchidae). Our reanalysis and exploration of their molecular sequence data shows that only a single gene, EGR3, of the six nuclear genes analysed by Mayden & Chen, is responsible for the position of Paedocypris as ‘the basal sister group to all Cypriniformes’. Three independent methods to visualize and analyse phylogenetic signal and conflict of data sets (phylogenetic networks, splits analysis methods or SAMS, and site‐wise likelihood analyses) reveal a high level of character conflict and noise in Mayden & Chen's data set. The ‘basal’ position of Paedocypris seems to be the outcome of the interplay of two long‐branch effects. We apply the same analytical methods to the data set from Rüber et al.'s molecular analysis of the phylogenetic position of Paedocypris and discuss our findings. We conclude that none of the molecular data sets compiled to date can establish the phylogenetic position of Paedocypris with confidence. Morphological data suggest that Paedocypris and Danionella are sister genera, and that their closest relative is Sundadanio, although the position of these three miniatures among cyprinoids is still unclear. © 2014 The Linnean Society of London