On the phylogenetic significance of sagittocysts and copulatory organs in acoel turbellarians

Viewed by SEM and TEM, sagittocysts of Convoluta bifoveolata Mamkaev, 1971, and needles of C. sagittifera Ivanov, 1952, have the same structure. Both are capsule-form extrusomes containing a protrusible needle. Only seven similar species of convolutimorph acoels symbiotic with green algae and C. sagittifera, without algae, possess extrusomes of this peculiar and complicated type. The sagittocyst is a clear synapomorphy of all these species. A sacciform ciliated antrum lacking a seminal vesicle is also characteristic of these species and also of three Japanese species of green (algae-symbiotic) convolutimorph acoels lacking sagittocysts. We suggest schemes of the possible evolution of male and female copulatory organs to provide a basis for better using such organs as phylogenetic characters. We regard the formation of a ciliated sacciform antrum as an independent evolutionary trend. This conclusion forms the basis for establishing the separate family Sagittiferidae. Species of this family seem to have originated in the West Pacific.     

Concordance of molecular and morphological data: The example of the Acoela

Morphological features of the Acoela appear to be quite plastic, including those of the copulatory organs, which provide the principle characteristics used for the systematics of this group. Consequently, classification schemes of the Acoela comprise numerous polyphyletic groupings. In this review, we detail recent revisions of acoel systematics using molecular sequence data and new and reevaluated morphological characteristics. Gene trees are discordant with traditional systematic schemes but strongly concordant with new morphological characteristics obtained through the use of transmission electron microscopy and confocal laser scanning microscopy, namely, characteristics of body-wall and copulatory organ musculature, sperm, sperm ducts, sagittocysts, and immunocytochemistry of the nervous system. This merger of molecular and morphological data has led to significant changes in acoel classification, including a major emendation of the largest family of the Acoela, the Convolutidae, whereby half of its members were transferred to a newly created family, the Isodiametridae.     

Walking on inclines: how do desert ants monitor slope and step length

Background

In order to increase the weak database concerning the organogenesis of Acoela – a clade regarded by many as the earliest extant offshoot of Bilateria and thus of particular interest for studies concerning the evolution of animal bodyplans – we analyzed the development of the musculature of Symsagittifera roscoffensis using F-actin labelling, confocal laserscanning microscopy, and 3D reconstruction software.

Results

At 40% of development between egg deposition and hatching short subepidermal fibres form. Muscle fibre development in the anterior body half precedes myogenesis in the posterior half. At 42% of development a grid of outer circular and inner longitudinal muscles is present in the bodywall. New circular muscles either branch off from present fibres or form adjacent to existing ones. The number of circular muscles is higher than that of the longitudinal muscles throughout all life cycle stages. Diagonal, circular and longitudinal muscles are initially rare but their number increases with time. The ventral side bears U-shaped muscles around the mouth, which in addition is surrounded by a sphincter muscle. With the exception of the region of the statocyst, dorsoventral muscles are present along the entire body of juveniles and adults, while adults additionally exhibit radially oriented internal muscles in the anterior tip. Outer diagonal muscles are present at the dorsal anterior tip of the adult. In adult animals, the male gonopore with its associated sexual organs expresses distinct muscles. No specific statocyst muscles were found. The muscle mantles of the needle-shaped sagittocysts are situated along the lateral edges of the animal and in the posterior end close to the male gonopore. In both juveniles and adults, non-muscular filaments, which stain positively for F-actin, are associated with certain sensory cells outside the bodywall musculature.

Conclusion

Compared to the myoanatomy of other acoel taxa, Symsagittifera roscoffensis shows a very complex musculature. Although data on presumably basal acoel clades are still scarce, the information currently available suggests an elaborated musculature with longitudinal, circular and U-shaped muscles as being part of the ancestral acoel bodyplan, thus increasing the possibility that Urbilateria likewise had a relatively complicated muscular ground pattern.     

How the worm got its pharynx: phylogeny, classification and Bayesian assessment of character evolution in Acoela

Acoela are marine microscopic worms currently thought to be the sister taxon of all other bilaterians. Acoels have long been used as models in evolutionary scenarios, and generalized conclusions about acoel and bilaterian ancestral features are frequently drawn from studies of single acoel species. There is no extensive phylogenetic study of Acoela and the taxonomy of the 380 species is chaotic. Here we use two nuclear ribosomal genes and one mitochondrial gene in combination with 37 morphological characters in an analysis of 126 acoel terminals (about one-third of the described species) to estimate the phylogeny and character evolution of Acoela. We present an estimate of posterior probabilities for ancestral character states at 31 control nodes in the phylogeny. The overall reconstruction signal based on the shape of the posterior distribution of character states was computed for all morphological characters and control nodes to assess how well these were reconstructed. The body-wall musculature appears more clearly reconstructed than the reproductive organs. Posterior similarity to the root was calculated by averaging the divergence between the posterior distributions at the nodes and the root over all morphological characters. Diopisthoporidae is the sister group to all other acoels and has the highest posterior similarity to the root. Convolutidae, including several "model" acoels, is most divergent. Finally, we present a phylogenetic classification of Acoela down to the family level where six previous family level taxa are synonymized.     

Lipid biosynthesis in the marine flatworm Convoluta roscoffensis and its algal symbiont Platymonas convoluta.

As a part of an investigations on the lipid metabolism in Platyhelminthes, the acoel Convoluta roscoffensis, which harbors the green alga Platymonas convoluta as a symbiont, was studied. Isotopic tracer experiments established that the acoel lacks the ability to synthesize de novo long-chain saturated and unsaturated fatty acids and depends on its algal symbiont for these compounds. The acoel's fatty acid composition closely resembles that of the alga but differs from those of other animals; the acoel's polyunsaturated fatty acids are of the plant type (omega 3 family) rather than of the animal type (omega 6 family). The acoel also lacks the ability to synthesize sterols de novo. It contains 24-methylenecholesterol synthesized by the algae and, in addition, significant amounts of cholesterol, which is probably a host modification product of the algal sterol. With fatty acids provided by the symbiont, the acoel has the ability to synthesize its own complex lipids. The acoel contains relatively large amounts of triglyceride, phosphatidylcholine, and ethanolamine plasmalogen. These compounds are either not present at all or present only in minute amounts in the symbiotic alga. Since acoels belong to the most primitive forms of the present-day flatworms, the observed metabolic defects in this organism suggest that mechanisms for the biosynthesis of fatty acids and sterols were lost early during the evolution of the Platyhelminthes, and that this phenomenon is widespread within the phylum.     

Electrophysiological properties of resting secretory membranes of lamellibranch mantles. Interaction between calcium and potassium

This study concerns the effects of ions on the shell-secreting membrane of clam mantles. The average resting potentials were --47 mV for freshwater mantles and --60 mV for marine mantles. Elevation of potassium in the absence of chloride gave a maximal slope of depolarization equivalent to 59 mV for a 10-fold change in the marine form but much less in the freshwater form. In normal potassium, a 10- fold reduction in calcium produced a hyperpolarization of 6 mV for the freshwater mantle. Neither reduction nor elevation of calcium affected the potential of marine mantles in the presence of normal potassium, but a hyperpolarization of 8 mV occurred when calcium was deleted in a low-potassium medium. Elevated calcium reduced the depolarization induced by raised potassium in both species and resulted in an increased effective membrane resistance in marine mantles. Lowered calcium enhanced the hyperpolarization caused by reduction in potassium in freshwater mantles but not in the marine species. Replacement of chloride by large anions produced transient depolarization in both freshwater and marine mantles and resulted in a maintained increased effective membrane resistance in marine mantles. The effects of sodium and magnesium on the membrane potential were not significant in normal potassium. We conclude that the secretory membrane of freshwater and marine clam mantles is permeable mainly to potassium and chloride, and that responses of the membrane potential to calcium are mediated through its effect on the permeability to potassium.     

Structure and evolution of the pharynx simplex in acoel flatworms (Acoela)

The homology of pharynges within the mostly pharynx‐less Acoela has been a matter of discussion for decades and even the basic question of whether a pharynx is a primitive trait within the Acoela and homologous to the pharynx of platyhelminth turbellarians is open. By using fluorescence staining of musculature, as well as conventional histological techniques and transmission electron microscopy, the present study sets focus on the mouth and pharynx (where present) of seven species of Acoela within Paratomellidae, Solenofilomorphidae, Hofsteniidae, Proporidae, and Convolutidae, as well as one species of Nemertodermatida and Catenulida, respectively. It is shown that among the investigated families of acoels there is a great variability in muscle systems associated with the mouth and pharynx and that pharynx histology and ultrastructural characters are widely diverse. There are no close similarities between the acoel pharynges and the catenulid pharynx but there is a general resemblance of the musculature associated with the mouth in the representatives of Paratomellidae and Nemertodermatida. On the basis of the profound differences in pharynx morphology, three major conclusions are drawn: 1) the pharynges as present in Recent acoels are not homologous to the pharynx simplex characteristic for Catenulida and Macrostomida within the Platyhelminthes; 2) the different muscular pharynx types of acoels are not homologous between higher taxa and thus a single acoel‐type pharynx simplex cannot be defined; 3) the presence of a muscular pharynx most likely does not represent the ancestral state. J. Morphol, 2009. © 2008 Wiley‐Liss, Inc.     

Ultrastructure and tubulin immunocytochemistry of the copulatory stylet-like structure in Childia species (Acoela)

One of the main characters used in acoel taxonomy is the male copulatory organ. Despite this, ultrastructural studies of this structure are scarce. We studied the ultrastructure of the copulatory organ in eight species of acoels belonging to the taxon Childia. Members of Childia possess a well-developed conical or cylindrical stylet-like structure composed of needles. Immunogold cytochemistry of tubulin was used to determine the composition of the needles. Stylet-like structures of Childia species at the ultrastructural level are basically similar. Stylet needles show intracellular differentiations. As shown both by ultrastructural and immunocytochemical methods, the stylet needles, in all species studied, are composed of long, parallel microtubules, either tightly packed or polymerized. We report unusual polymerization of microtubules, resulting in formation of a honeycomb-like structure in cross section. Variations of ultrastructure among Childia species include numbers and arrangement of stylet needles, shape of needles, needle compactness, microtubule polymerization, direction of stylet growth, and presence/absence of different types of granules. The stylet-like structures are homologous within Childia, but are likely to prove nonhomologous with the other needle-like structures found in acoel copulatory organs. Stylets in Platyhelminthes are not homologous with stylet-like structures in acoels.     

Systematic revision of acoels with 9+0 sperm ultrastructure (Convolutida) and the influence of sexual conflict on morphology

We have used newly discerned morphological characters as well as molecular‐sequence data from 18S and 28S rDNA to revise the families recently designated as the ‘9+0’ acoels – what we call Convolutida. Characters from the ultrastructure of sperm, with their ‘9+0’ axonemes, are useful in delineating the Convolutida, but are either species‐specific or too conserved within the group to be used to infer relationships within it. Male genital organs, prostatoid organs, and sagittocysts, on the other hand, give a good phylogenetic signal for reconstructing relationships of such genera as Conaperta, Anaperus, and Achoerus; some features of the reproductive organs correlate with habitat and show how the Convolutida probably originated as epiphytic predators and radiated into the mesopsammon, pelagic, and coral‐associated realms. In this revision of the Convolutida we provide revised synopses of its families – which we restrict to the Anaperidae, Convolutidae, and Sagittiferidae – and describe a new species, Polychoerus gordoni, from New Zealand. We transfer the genus Adenopea from the Antroposthiidae to the Convolutidae; Conaperta, Neochildia, and Oxyposthia from the Convolutidae to the Anaperidae; Paranaperus and Praeanaperus from the Anaperidae to the Haploposthiidae. Convoluta aegyptica is synonymized with Convoluta boehmigi, Convoluta lacazii with Convoluta sordida, and the genus Picola (Convolutidae) with Deuterogonaria (Haploposthiidae). Amphiscolops blumi, A. carvalhoi, and A. langerhansi, all of which possess a cellular seminal bursa, are transferred to the genus Heterochaerus. Convoluta elegans and Pseudanaperus tinctus are classified as nomina nuda. We use our findings on the ultrastructure of female genital organs and spermatozoa to show that sexual conflict plays a major role in the evolution of diversity of these structures and that the phylogeny of the Acoela would comprise early forms without female genital organs and hyper‐ or hypodermal transfer of sperm through advanced forms with ever longer and narrower bursal nozzles and sperm with axial microtubules. Moreover, our results show that the acquisition of endosymbiotic algae happened at least twice within the Acoela.     

Embryonic muscle development of Convoluta pulchra (Turbellaria-acoelomorpha, platyhelminthes)

We studied the embryonic development of body-wall musculature in the acoel turbellarian Convoluta pulchra by fluorescence microscopy using phalloidin-bound stains for F-actin. During stage 1, which we define as development prior to 50% of the time between egg-laying and hatching, actin was visible only in zonulae adhaerentes of epidermal cells. Subsequent development of muscle occurred in two distinct phases: first, formation of an orthogonal grid of early muscles and, second, differentiation of other myoblasts upon this grid. The first elements of the primary orthogonal muscle grid appeared as short, isolated, circular muscle fibers (stage 2; 50% developmental time), which eventually elongated to completely encircle the embryo (stage 3; at 60% of total developmental time). The first primary longitudinal fibers appeared later, along with some new primary circular fibers, by 60-63% of total developmental time (stage 4). From 65 to 100% of total developmental time (stages 5 to 7), secondary fibers, using primary fibers as templates, arose; the number of circular and longitudinal muscles thus increased, and at the same time parenchymal muscles began appearing. Hatchlings (stage 8) possessed about 25 circular and 30 longitudinal muscles as well as strong parenchymal muscles. The remarkable feature of the body wall of many adult acoel flatworms is that longitudinal muscles bend medially and cross each other behind the level of the mouth. We found that this development starts shortly after the appearance of the ventral mouth opening within the body wall muscle grid. The adult organization of the body-wall musculature consists of a grid of several hundred longitudinal and circular fibers and a few diagonal muscles. Musculature of the reproductive organs developed after hatching. Thus, extensive myogenesis must occur also during postembryonic development. Comparison between the turbellarians and the annelids suggests that formation of a primary orthogonal muscle grid and its subsequent use as a template for myoblast differentiation are the two basic developmental phases in vermiform Spiralia if not in the Bilateria as a whole. Finally, our new data suggest that for the Acoela the orthogonal primary patterning of longitudinal and circular muscles in the body wall is achieved without using originally positional information of the nervous system.     

Acoel flatworms are not platyhelminthes: evidence from phylogenomics

Acoel flatworms are small marine worms traditionally considered to belong to the phylum Platyhelminthes. However, molecular phylogenetic analyses suggest that acoels are not members of Platyhelminthes, but are rather extant members of the earliest diverging Bilateria. This result has been called into question, under suspicions of a long branch attraction (LBA) artefact. Here we re-examine this problem through a phylogenomic approach using 68 different protein-coding genes from the acoel Convoluta pulchra and 51 metazoan species belonging to 15 different phyla. We employ a mixture model, named CAT, previously found to overcome LBA artefacts where classical models fail. Our results unequivocally show that acoels are not part of the classically defined Platyhelminthes, making the latter polyphyletic. Moreover, they indicate a deuterostome affinity for acoels, potentially as a sister group to all deuterostomes, to Xenoturbellida, to Ambulacraria, or even to chordates. However, the weak support found for most deuterostome nodes, together with the very fast evolutionary rate of the acoel Convoluta pulchra, call for more data from slowly evolving acoels (or from its sister-group, the Nemertodermatida) to solve this challenging phylogenetic problem.     

Molecular architecture of muscles in an acoel and its evolutionary implications

We have characterized the homologs of an actin, a troponin I, and a tropomyosin gene in the acoel Symsagittifera roscoffensis. These genes are expressed in muscles and most likely coexpressed in at least a subset of them. In addition, and for the first time for Acoela, we have produced a species-specific muscular marker, an antibody against the tropomyosin protein. We have followed tropomyosin gene and protein expression during postembryonic development and during the posterior regeneration of amputated adults, showing that preexisting muscle fibers contribute to the wound closure. The three genes characterized in this study interact in the striated muscles of vertebrates and invertebrates, where troponin I and tropomyosin are key regulators of the contraction of the sarcomere. S. roscoffensis and all other acoels so far described have only smooth muscles, but the molecular architecture of these is the same as that of striated fibers of other bilaterians. Given the proposed basal position of acoels within the Bilateria, we suggest that sarcomeric muscles arose from a smooth muscle type, which had the molecular repertoire of striated musculature already in place. We discuss this model in a broad comparative perspective.     

The unique developmental program of the acoel flatworm, Neochildia fusca

Acoel embryos exhibit a unique form of development that some investigators argue is related to that found in polyclad turbellarians and coelomate spiralians, which display typical quartet spiral cleavage. We generated the first cell-lineage fate map for an acoel flatworm, Neochildia fusca, using modern intracellular lineage tracers to assess the degree of similarity between these distinct developmental programs. N. fusca develops via a "duet" cleavage pattern in which second cleavage occurs in a leiotropically oblique plane relative to the animal-vegetal axis. At the four-cell stage, the plane of first cleavage corresponds to the plane of bilateral symmetry. All remaining cleavages are symmetrical across the sagittal plane. No ectomesoderm is formed; the first three micromere duets generate only ectodermal derivatives. Endomesoderm, including the complex assemblage of circular, longitudinal, and oblique muscle fibers, as well as the peripheral and central parenchyma, is generated by both third duet macromeres. The cleavage pattern, fate map, and origins of mesoderm in N. fusca share little similarity to that exhibited by other spiralians, including the Platyhelminthes (e.g., polyclad turbellarians). These findings are considered in light of the possible evolutionary origins of the acoel duet cleavage program versus the more typical quartet spiral cleavage program. Finally, an understanding of the cell-lineage fate map allows us to interpret the results of earlier cell deletion studies examining the specification of cell fates within these embryos and reveals the existence of cell-cell inductive interactions in these embryos.     

Elongation factor 1-alpha sequences do not support an early divergence of the Acoela

The phylogenetic position of the Acoela is a key problem in the understanding of metazoan evolution. Recent studies based on 18S ribosomal DNA (rDNA) sequences have placed the Acoela in an extremely basal position as the sister group to all other extant triploblastic animals, suggesting that the phylum Platyhelminthes is polyphyletic. In order to test the results obtained with 18S rDNA, we sequenced elongation factor 1-alpha (EF1a) for the acoel Convoluta roscoffensis and five species of Turbellaria (two polyclads, Leptoplana tremellaris, and Prostheceraeus vittatus, and three triclads, Crenobia alpina, Schmidtea polychroa, and Girardia tigrina). Phylogenetic analyses of EF1a sequences show that the acoel sequences branch within the Platyhelminthes, in opposition to the 18S rDNA data. Moreover, comparison of the central variable region of EF1a shows similar sequence signatures between C. roscoffensis and the three triclad species. Although EF1a sequences fail to prove the monophyly of the phylum Platyhelminthes, they do not confirm the early divergence of the Acoela.     

SALMFamide2 and serotonin immunoreactivity in the nervous system of some acoels (Xenacoelomorpha)

Acoel worms are simple, often microscopic animals with direct development, a multiciliated epidermis, a statocyst, and a digestive parenchyma instead of a gut epithelium. Morphological characters of acoels have been notoriously difficult to interpret due to their relative scarcity. The nervous system is one of the most accessible and widely used comparative features in acoels, which have a so‐called commissural brain without capsule and several major longitudinal neurite bundles. Here, we use the selective binding properties of a neuropeptide antibody raised in echinoderms (SALMFamide2, or S2), and a commercial antibody against serotonin (5‐HT) to provide additional characters of the acoel nervous system. We have prepared whole‐mount immunofluorescent stainings of three acoel species: Symsagittifera psammophila (Convolutidae), Aphanostoma pisae, and the model acoel Isodiametra pulchra (both Isodiametridae). The commissural brain of all three acoels is delimited anteriorly by the ventral anterior commissure, and posteriorly by the dorsal posterior commissure. The dorsal anterior commissure is situated between the ventral anterior commissure and the dorsal posterior commissure, while the statocyst lies between dorsal anterior and dorsal posterior commissure. S2 and serotonin do not co‐localise, and they follow similar patterns to each other within an animal. In particular, S2, but not 5‐HT, stains a prominent commissure posterior to the main (dorsal) posterior commissure. We have for the first time observed a closed posterior loop of the main neurite bundles in S. psammophila for both the amidergic and the serotonergic nervous system. In I. pulchra, the lateral neurite bundles also form a posterior loop in our serotonergic nervous system stainings.     

Evolution of body-wall musculature in the Platyhelminthes (Acoelomorpha, Catenulida, Rhabditophora)

In an effort to understand the phylogeny of the Platyhelminthes, the patterns of body-wall musculature of flatworms were studied using fluorescence microscopy and Alexa-488-labeled phalloidin. Species of the Catenulida have a simple orthogonal gridwork of longitudinal and circular muscles. Members of the Rhabditophora have the same gridwork of musculature, but also have diagonal muscles over their entire body. Although a few species of Acoelomorpha possessed a simple orthogonal grid of musculature, most species typically have distinctly different patterns of dorsal and ventral body-wall musculature that include sets of longitudinal, circular, U-shaped, and several kinds of diagonal muscles. Several distinct patterns of musculature were identified, including 8 patterns in 11 families of acoels. These patterns have proven to be useful in clarifying the phylogeny of the Acoelomorpha, particularly with regard to the higher acoels. Patterns of musculature as well as other morphological characters are used here for revisions of acoel systematics, including the return of Eumecynostomum sanguineum (Mecynostomidae) to the genus Aphanostoma (Convolutidae), the revision of the family Childiidae, and the formation of a new family, Actinoposthiidae.     

Fungal relationships and structural identity of their ectomycorrhizae

Aproximately 5,000–6,000 fungal species form ectomyorrhizae (ECM), the symbiotic organs with roots of predominantly trees. The contributing fungi are not evenly distributed over the system of fungi. Within Basidiomycota exclusively Hymenomycetes and within Ascomycota exclusively Ascomycetes contribute to the symbiosis. Hymenomycetes play a big part, Ascomycetes a minor role; Zygomycetes only form exceptionally ECM. Responsible for ascomycetous ECM are mostly Pezizales with their hypogeous derivatives, whereas Boletales, Gomphales, Thelephorales, Amanitaceae, Cantharellaceae, Cortinariaceae, Russulaceae, and Tricholomataceae are the most important ectomycorrhizal relationships within Hymenomycetes. ECM, as transmitting organs between soil and roots, are transporting carbohydrates for growth of mycelium and fruitbodies from roots and have to satisfy the tree’s demand for water and nutrients. The latter task particularly influences the structure of ECM as nutrients are patchily distributed in the soil and saprotrophic as well as ectomycorrhizal fungi can act as strong competitors for nutrients. In focusing these requirements, ECM developed variously structured hyphal sheaths around the roots, the so-called mantles, and differently organized mycelium that emanates from the mantle, the so-called extramatrical mycelium. The mantles can be plectenchymatous consisting of loosely woven, differently arranged hyphae or they are densely packed, forming a pseudoparenchyma similar to the epidermis of leaves. The extramatrical mycelium grows either as simple scattered hyphae from the mantle into the soil or it can be united to undifferentiated rhizomorphs with a small reach or to highly organized root-like organs with vessel-like hyphae for efficient water and nutrient transport from distances of decimeters. Cystidia, sterile and variously shaped hyphal ends, possibly appropriate for preventing animal attack, in addition, can cover mantles and rhizomorphs. Although only a limited number of species could be considered, some general conclusions are possible.The genus Tuber forms needle-shaped cystidia and lacks rhizomorphs and clamps. Gomphales ECM are identified by rhizomorphs with ampullate inflations at septa of some hyphae and by oleoacanthocystidia or/and oleoacanthohyphae. Thelephoraceae reveal a great diversity of mantle structures and of extramatrical mycelium, with some additional optional characters, i.e., dark brown color, cystidia, blue granules, amyloid hyphae, or amyloid septa. Bankeraceae are mostly characterized by plectenchymatous mantles with star-like pattern and chlamydospores. Russulaceae possess smooth and hydrophilic ECM. Russula forms plectenchymatous mantles with knob-bearing cystidia, so-called russuloid cystidia, or pseudoparenchymatous mantles without cystidia. Lactarius lacks cystidia and shows laticifers within plectenchymatous or within pseudoparenchymatous mantles. The Boletales families Boletaceae, Gyroporaceae, Melanogastraceae, Paxillaceae, Rhizopogonaceae, Sclerodermataceae, and Suillaceae have the most advanced rhizomorph type, the so-called boletoid rhizomorphs, and reveal generally plectenchymatous mantles, frequently with ring-like patterns. Gomphidiaceae and Albatrellaceae provide cystidia, plectenchymatous mantles, and amyloidy; Gomphidiaceae are generally growing in ECM of Suillaceae and Rhizopogonaceae. Cortinariaceae reveal plectenchymatous mantles and undifferentiated or differentiated rhizomorphs or lack rhizomorphs at all. Cortinarius and Dermocybe are distinct by irregularly shaped, bent to tortuous ECM with many rhizomorphs, some growing over the mycorrhizal tip into the soil. Inocybe lacks rhizomorphs and its emanating hyphae are furnished by many secondary septa and prominent clamps with a hole. Rozites lacks rhizomorphs, too, and reveals a distinctly amyloid gelatinous mantle matrix. Descolea and Descomyces are covered by bolbitioid cystidia. Lastly, the genus Tricholoma forms plectenchymatous mantles and a high diversity of rhizomorphs. Some of the ectomycorrhizal features are used to hypothesize relationships at different taxonomic levels. These conclusions are compared with recently developed molecular hypotheses. Correspondence between the two types of hypotheses are evident, while some conflicts wait for a settlement.     

Molecular systematics of the Acoela (Acoelomorpha,Platyhelminthes) and its concordance with morphology

The phylogenetic relationships of the lower worm group Acoela were investigated using newly obtained nuclear 18S rDNA sequences from 16 acoels in combination with 16 acoel sequences available on GenBank from other laboratories. Parsimony and maximum likelihood analyses of the molecular data supported the concept that the Acoela is monophyletic; however, the gene tree produced by these analyses conflicts with the current taxonomic system for the Acoela in several family-level groupings. Most notable is the apparent polyphyly of the largest family of acoels, the Convolutidae. DNA analysis grouped together species of small-bodied convolutids in one clade, while large-bodied convolutids grouped in a separate clade with other large-bodied acoels. Despite such conflicts, the branching pattern in the gene tree is well supported by morphological characters of sperm and body-wall musculature.