The syndermatan phylogeny and the evolution of acanthocephalan endoparasitism as inferred from 18S rDNA sequences

The phylogeny of the Syndermata (Rotifera: Monogononta, Bdelloidea, Seisonidea; Acanthocephala: Palaeacanthocephala, Eoacanthocephala, Archiacanthocephala) is key to understanding the evolution of acanthocephalan endoparasitism from free-living ancestors. In the present study, maximum likelihood, distance/neighbor-joining, and maximum parsimony analyses have been carried out based on 18S rDNA data of 22 species (four new sequences). The results suggest a monophyletic origin of the Eurotatoria (Monogononta+Bdelloidea). Seison appears as the acanthocephalan sistergroup. Palaeacanthocephala split into an "Echinorhynchus"-and a "Leptorhynchoides"-group, the latter sharing a monophyletic origin with the Eoacanthocephala and Archiacanthocephala. As inferred from the phylogeny obtained acanthocephalan endoparasitism evolved from a common ancestor of Seison and Acanthocephala that lived epizoically on an early mandibulate. Probably, an acanthocephalan stem species invaded the mandibulate host, thus establishing an endoparasitic lifestyle. Subsequently, vertebrates (or gnathostomes) became part of the parasite's life cycle. In the stem line of the Archiacanthocephala, a terrestrial life cycle has evolved, with an ancestor of the Tracheata (Insecta, Myriapoda) acting as intermediate host.     

A Mitogenomic Re-Evaluation of the Bdelloid Phylogeny and Relationships among the Syndermata

Molecular and morphological data regarding the relationships among the three classes of Rotifera (Bdelloidea, Seisonidea, and Monogononta) and the phylum Acanthocephala are inconclusive. In particular, Bdelloidea lacks molecular-based phylogenetic appraisal. I obtained coding sequences from the mitochondrial genomes of twelve bdelloids and two monogononts to explore the molecular phylogeny of Bdelloidea and provide insight into the relationships among lineages of Syndermata (Rotifera + Acanthocephala). With additional sequences taken from previously published mitochondrial genomes, the total dataset included nine species of bdelloids, three species of monogononts, and two species of acanthocephalans. A supermatrix of these 10-12 mitochondrial proteins consistently recovered a bdelloid phylogeny that questions the validity of a generally accepted classification scheme despite different methods of inference and various parameter adjustments. Specifically, results showed that neither the family Philodinidae nor the order Philodinida are monophyletic as currently defined. The application of a similar analytical strategy to assess syndermate relationships recovered either a tree with Bdelloidea and Monogononta as sister taxa (Eurotatoria) or Bdelloidea and Acanthocephala as sister taxa (Lemniscea). Both outgroup choice and method of inference affected the topological outcome emphasizing the need for sequences from more closely related outgroups and more sophisticated methods of analysis that can account for the complexity of the data.     

EST based phylogenomics of Syndermata questions monophyly of Eurotatoria

Background  

The metazoan taxon Syndermata comprising Rotifera (in the classical sense of Monogononta+Bdelloidea+Seisonidea) and Acanthocephala has raised several hypotheses connected to the phylogeny of these animal groups and the included subtaxa. While the monophyletic origin of Syndermata and Acanthocephala is well established based on morphological and molecular data, the phylogenetic position of Syndermata within Spiralia, the monophyletic origin of Monogononta, Bdelloidea, and Seisonidea and the acanthocephalan sister group are still a matter of debate. The comparison of the alternative hypotheses suggests that testing the phylogenetic validity of Eurotatoria (Monogononta+Bdelloidea) is the key to unravel the phylogenetic relations within Syndermata. The syndermatan phylogeny in turn is a prerequisite for reconstructing the evolution of the acanthocephalan endoparasitism.     

Evidence from a protein-coding gene that acanthocephalans are rotifers

Abstract. Rotifera and Acanthocephala are generally regarded as separate phyla sharing a basal position among triploblast protostomes. This paper presents the first molecular phylogenetic examination of the relationship of Acanthocephala to all three rotifer classes, Seisonidea, Monogononta, and Bdelloidea. Inclusion of Acanthocephala within Rotifera, probably as a sister-taxon to a clade composed of Bdelloidea and Monogononta (the Eurotatoria), is strongly supported by both parsimony and distance methods, using a region of the nuclear coding gene hsp82. Previous molecular evidence for the inclusion of Acanthocephala in the Rotifera suggested that Acanthocephala is a sister-taxon of Bdelloidea, forming the clade Lemniscea. No support is found for this clade, and evidence is presented that the monogonont rotifer used in those analyses, Brachionus plicatilis , may be evolving in an anomalous manner.     

The complete mitochondrial genome sequence of Oncicola luehei (Acanthocephala: Archiacanthocephala) and its phylogenetic position within Syndermata

In the present study, we determined the complete mitochondrial genome sequence of Oncicola luehei (14,281bp), the first archiacanthocephalan representative and the second complete sequence from the phylum Acanthocephala. The complete genome contains 36 genes including 12 protein coding genes, 22 transfer RNA (tRNA) genes and 2 ribosomal RNA genes (rrnL and rrnS) as reported for other syndermatan species. All genes are encoded on the same strand. The overall nucleotide composition of O. luehei mtDNA is 37.7% T, 29.6% G, 22.5% A, and 10.2% C. The overall A+T content (60.2%) is much lower, compared to other syndermatan species reported so far, due to the high frequency (18.3%) of valine encoded by GTN in its protein-coding genes. Results from phylogenetic analyses of amino acid sequences for 10 protein-coding genes from 41 representatives of major metazoan groups including O. luehei supported monophyly of the phylum Acanthocephala and of the clade Syndermata (Acanthocephala+Rotifera), and the paraphyly of the clade Eurotatoria (classes Bdelloidea+Monogononta from phylum Rotifera). Considering the position of the acanthocephalan species within Syndermata, it is inferred that obligatory parasitism characteristic of acanthocephalans was acquired after the common ancestor of acanthocephalans diverged from its sister group, Bdelloidea. Additional comparison of complete mtDNA sequences from unsampled acanthocephalan lineages, especially classes Polyacanthocephala and Eoacanthocephala, is required to test if mtDNA provides reliable information for the evolutionary relationships and pattern of life history diversification found in the syndermatan groups.     

Phylogenetic analyses of endoparasitic Acanthocephala based on mitochondrial genomes suggest secondary loss of sensory organs

The metazoan taxon Syndermata (Monogononta, Bdelloidea, Seisonidea, Acanthocephala) comprises species with vastly different lifestyles. The focus of this study is on the phylogeny within the syndermatan subtaxon Acanthocephala (thorny-headed worms, obligate endoparasites). In order to investigate the controversially discussed phylogenetic relationships of acanthocephalan subtaxa we have sequenced the mitochondrial (mt) genomes of Echinorhynchus truttae (Palaeacanthocephala), Paratenuisentis ambiguus (Eoacanthocephala), Macracanthorhynchus hirudinaceus (Archiacanthocephala), and Philodina citrina (Bdelloidea). In doing so, we present the largest molecular phylogenetic dataset so far for this question comprising all major subgroups of Acanthocephala. Alongside with publicly available mt genome data of four additional syndermatans as well as 18 other lophotrochozoan (spiralian) taxa and one outgroup representative, the derived protein-coding sequences were used for Maximum Likelihood as well as Bayesian phylogenetic analyses. We achieved entirely congruent results, whereupon monophyletic Archiacanthocephala represent the sister taxon of a clade comprising Eoacanthocephala and monophyletic Palaeacanthocephala (Echinorhynchida). This topology suggests the secondary loss of lateral sensory organs (sensory pores) within Palaeacanthocephala and is further in line with the emergence of apical sensory organs in the stem lineage of Archiacanthocephala.     

Broad taxonomic sampling of mitochondrial cytochrome c oxidase subunit I does not solve the relationships between Rotifera and Acanthocephala

The phylogenetic relationships within Syndermata (Acanthocephala + Rotifera) are still unresolved. Cladistic morphological analyses support monophyly of Rotifera and Eurotatoria (Bdelloidea + Monogononta), while molecular phylogenies of 18S, 28S, COI, hsp82 and EST propose different topologies, with at least six contrasting scenarios. All these phylogenies are characterized by poor taxon sampling; thus, our aim is to solve the relationships within Syndermata sampling as many sequences as possible from one single locus. We reconstructed phylogenetic relationship using more than 1000 sequences of COI. We performed Maximum Likelihood and Bayesian phylogenetic reconstructions on amino acid alignments, using either Gnathostomulida or Platyhelminthes as an outgroup, and then we performed SH tests to provide confidence on the best phylogenetic hypotheses. All four major clades (Acanthocephala, Bdelloidea, Monogononta and Seisonidea) are always highly supported. The basal relationship among the four clades is not consistently resolved by any of the phylogenetic reconstructions; nevertheless, there is a strong support for a clade of Acanthocephala + Bdelloidea from the SH tests, in agreement with other phylogenies from ribosomal genes and EST analyses.     

Phylogenetic Relationships of Acanthocephala Based on Analysis of 18S Ribosomal RNA Gene Sequences

Acanthocephala (thorny-headed worms) is a phylum of endoparasites of vertebrates and arthropods, included among the most phylogenetically basal tripoblastic pseudocoelomates. The phylum is divided into three classes: Archiacanthocephala, Palaeacanthocephala, and Eoacanthocephala. These classes are distinguished by morphological characters such as location of lacunar canals, persistence of ligament sacs in females, number and type of cement glands in males, number and size of proboscis hooks, host taxonomy, and ecology. To understand better the phylogenetic relationships within Acanthocephala, and between Acanthocephala and Rotifera, we sequenced the nearly complete 18S rRNA genes of nine species from the three classes of Acanthocephala and four species of Rotifera from the classes Bdelloidea and Monogononta. Phylogenetic relationships were inferred by maximum-likelihood analyses of these new sequences and others previously determined. The analyses showed that Acanthocephala is the sister group to a clade including Eoacanthocephala and Palaeacanthocephala. Archiacanthocephala exhibited a slower rate of evolution at the nucleotide level, as evidenced by shorter branch lengths for the group. We found statistically significant support for the monophyly of Rotifera, represented in our analysis by species from the clade Eurotatoria, which includes the classes Bdelloidea and Monogononta. Eurotatoria also appears as the sister group to Acanthocephala. Received: 12 October 1999 / Accepted: 8 February 2000     

Bayesian and Maximum Likelihood Analyses of Rotifer–Acanthocephalan Relationships

Rotifera is composed of groups with unusual ultrastructural, physiological, and reproductive characters. Our ability to understand the evolution of these features is complicated by the fact that the phylogenetic relationships among the three traditional rotifer groups (Seisonidea, Monogononta, and Bdelloidea) and Acanthocephala remain unresolved. Here, I present maximum likelihood and Bayesian analyses of rotifer–acanthocephalan relationships using both the protein-coding gene hsp82 and a combined data set of hsp82 and ribosomal small subunit (SSU) DNA sequences, using nucleotide and codon based models of evolution. Statistical analysis of the phylogenetic support for any of the likely relationships among rotifer groups suggests that more than a combined hsp82 + SSU data set will be needed to resolve rotifer–acanthocephalan phylogeny with any degree of certainty.     

Lophotrochozoan phylogeny assessed with LSU and SSU data: evidence of lophophorate polyphyly

Of the three major bilaterian clades, Lophotrochozoa has the greatest diversity and disparity of body forms and is the least understood in terms of phylogenetic history. Within this clade, small nuclear ribosomal subunit (SSU or 18S) studies have failed to provide resolution and other molecular markers have insufficient taxon sampling. To examine relationships within Lophotrochozoa, we collected and complied complete SSU data and nearly complete (>90%) large nuclear ribosomal subunit (LSU or 28S) data totaling approximately 5kb per taxon, for 36 lophotrochozoans. Results of LSU and combined SSU+LSU likelihood analyses provide topologies more consistent with morphological data than analyses of SSU data alone. Namely, most phyla recognized on morphological grounds are recovered as monophyletic entities when the LSU data is considered (contra SSU data alone). These new data show with significant support that "Lophophorata" (traditionally recognized to include Brachiopoda, Phoronida, and Bryozoa) is not a monophyletic entity. Further, the data suggest that Platyzoa is real and may be derived within lophotrochozans rather than a basal or sister taxon. The recently discovered Cycliophora are allied to entoprocts, consistent with their initial placement based on morphology. Additional evidence for Syndermata (i.e., Rotifera+Acanthocephala) is also found. Although relationships among groups with trochophore-like larvae could not be resolved and nodal support values are generally low, the addition of LSU data is a considerable advance in our understanding of lophotrochozoan phylogeny from the molecular perspective.     

A modern approach to rotiferan phylogeny: combining morphological and molecular data

The phylogeny of selected members of the phylum Rotifera is examined based on analyses under parsimony direct optimization and Bayesian inference of phylogeny. Species of the higher metazoan lineages Acanthocephala, Micrognathozoa, Cycliophora, and potential outgroups are included to test rotiferan monophyly. The data include 74 morphological characters combined with DNA sequence data from four molecular loci, including the nuclear 18S rRNA, 28S rRNA, histone H3, and the mitochondrial cytochrome c oxidase subunit I. The combined molecular and total evidence analyses support the inclusion of Acanthocephala as a rotiferan ingroup, but do not support the inclusion of Micrognathozoa and Cycliophora. Within Rotifera, the monophyletic Monogononta is sister group to a clade consisting of Acanthocephala, Seisonidea, and Bdelloidea-for which we propose the name Hemirotifera. We also formally propose the inclusion of Acanthocephala within Rotifera, but maintaining the name Rotifera for the new expanded phylum. Within Monogononta, Gnesiotrocha and Ploima are also supported by the data. The relationships within Ploima remain unstable to parameter variation or to the method of phylogeny reconstruction and poorly supported, and the analyses showed that monophyly was questionable for the families Dicranophoridae, Notommatidae, and Brachionidae, and for the genus Proales. Otherwise, monophyly was generally supported for the represented ploimid families and genera.     

Acanthocephalan phylogeny and the evolution of parasitism

The study of parasite evolution relies on the identification of free-living sister taxa of parasitic lineages. Most lineages of parasitic helminths are characterized by an amazing diversity of species that complicates the resolution of phylogenetic relationships. Acanthocephalans offer a potential model system to test various long-standing hypotheses and generalizations regarding the evolution of parasitism in metazoans. The entirely parasitic Acanthocephala have a diversity of species that is manageable with regards to constructing global phylogenetic hypotheses, exhibit variation in hosts and habitats, and are hypothesized to have close phylogenetic affinities to the predominately free-living Rotifera. In this paper, I review and test previous hypotheses of acanthocephalan phylogenetic relationships with analyses of the available 18S rRNA sequence database. Maximum-parsimony and maximum-likelihood inferred trees differ significantly with regard to relationships among acanthocephalans and rotifers. Maximum-parsimony analysis results in a paraphyletic Rotifera, placing a long-branched bdelloid rotifer as the sister taxon of Acanthocephala. Maximum-likelihood analysis results in a monophyletic Rotifera. The difference between the two optimality criteria is attributed to long-branch attraction. The two analyses are congruent in terms of relationships within Acanthocephala. The three sampled classes are monophyletic, and the Archiacanthocephala is the sister taxon of a Palaeacanthocephala + Eoacanthocephala clade. The phylogenetic hypothesis is used to assess the evolution of host and habitat preferences. Acanthocephalan lineages have exhibited multiple radiations into terrestrial habitats and bird and mammal definitive hosts from ancestral aquatic habitats and fish definitive hosts, while exhibiting phylogenetic conservatism in the type of arthropod intermediate host utilized.     

Old and new data on Seisonidea (Rotifera)

Class Seisonidea consists of one marine genus, Seison, with two species (S. nebaliae and S. annulatus) which are epizoic on the crustacean Nebalia. Seisonidea are the only rotifers whose reproduction is strictly bisexual. They also possess the unusual feature of having well-developed males. In this paper we review the literature concerning biogeographical distribution, relationships with their host, and morphology, and present new information obtained with SEM and optical microscopy of both living animals and serial sections.Some seisonid characters, such as the paired retrocerebral organ, nervous system, and trophi, suggest that they hold a primitive position within phylum Rotifera. However, they do share features with other rotifers: paired gonads and an unusual locomotory behavior with Bdelloidea; lateral antennae, cellular stomach wall, arrangement of intracytoplasmic lamina, and other characters with Monogononta. Some features are peculiar to Seison: obligatory amphimixis, endolecythal eggs, encysted spermatozoa, unique mastax, and absence of copulatory organ in males and of vitellaria in females. Reduction of the corona and absence of resistant stages in Seisonidea may be related to their habitat and to their life style. We propose a closer relationship of Seisonidea to Monogononta than previously asserted.     

Early contributions of molecular phylogenetics to understanding the evolution of Rotifera

The past decade has seen the application of DNA sequence data to phylogenetic investigations of Rotifera, both expanding and challenging our understanding of the evolution of the phylum. Evidence that Acanthocephala, long regarded as a separate but closely related phylum, is a highly derived class of Rotifera demonstrates the potential of molecular analyses to suggest relationships not obvious from morphological analysis. Phylogenies based on the sequence of the gene for the small ribosomal RNA suggest that rotifers and acanthocephalans are associated with Platyhelminthes and Gastrotricha, perhaps in a clade with Gnathostomula and Cycliophora; at present, this group lacks a clear morphological synapomorphy. A more complete resolution of the molecular phylogeny of Rotifera will require surveying multiple genes and several species from each clade under investigation.     

强壮粗体虫的线粒体基因组及棘头虫的系统发育研究

通过长距离PCR方法,克隆了鳜（Siniperca chuatsi Basilewsky）肠道内寄生虫强壮粗体虫（Hebesoma violentum Van Cleave）线粒体基因组全长序列,共13393 bp （GenBank登录号:KC415004）,有36个基因,其中蛋白编码基因12个,核糖体基因2个,tRNA22个。所有基因均由线粒体基因组同一条链按同一个方向转录。利用该线粒体基因组和已经报道的一些轮虫纲种类的线粒体基因组序列,构建了棘头虫和轮虫的系统发育树。系统发育研究表明:包括强壮粗体虫、隐藏新棘虫Pallisentis celatus（Van Cleave）和Paratenuisentis ambiguous（Van Cleave）在内的始新棘头虫纲（Eoacanthocephala）与古棘头虫纲（Palaeacanthocephala）亲缘关系较近,聚为一枝后再与原棘头虫纲（Archiacanthocephala）聚在一起;棘头虫与双巢类轮虫（Bdelloid）亲缘关系最近,聚为一枝,然后再与单巢类轮虫（Monogonont）聚在一起,表明棘头虫和轮虫具有较近的亲缘关系。       

Phylogenetic relationships of the Acanthocephala inferred from 18S ribosomal DNA sequences

Phylogenetic relationships within the Acanthocephala have remained unresolved. Past systematic efforts have focused on creating classifications with little consideration of phylogenetic methods. The Acanthocephala are currently divided into three major taxonomic groups: Archiacanthocephala, Palaeacanthocephala, and Eoacanthocephala. These groups are characterized by structural features in addition to the taxonomy and habitat of hosts parasitized. In this study the phylogenetic relationships of 11 acanthocephalan species are examined with 18S rDNA sequences. Maximum parsimony, minimum evolution, and maximum likelihood methods are used to estimate phylogenetic relationships. Within the context of sampled taxa, all phylogenetic analyses are consistent with monophyly of the major taxonomic groups of the Acanthocephala, suggesting that the current higher order classification is natural. The molecular phylogeny is used to examine patterns of character evolution for various structural and ecological characteristics of the Acanthocephala. Arthropod intermediate host distributions, when mapped on the phylogeny, are consistent with monophyletic groups of acanthocephalans. Vertebrate definitive host distributions among the Acanthocephala display independent radiations into similar hosts. Levels of uncorrected sequence divergence among acanthocephalans are high; however, relative-rate tests indicate significant departure from rate uniformity among acanthocephalans, arthropods, and vertebrates. This precludes comparison of 18S divergence levels to assess the relative age of the Acanthocephala. However, other evidence suggests an ancient origin of the acanthocephalan-arthropod parasitic association.     

Phylogenetic analysis based on 18S ribosomal RNA gene sequences supports the existence of class polyacanthocephala (acanthocephala)

Members of phylum Acanthocephala are parasites of vertebrates and arthropods and are distributed worldwide. The phylum has traditionally been divided into three classes, Archiacanthocephala, Palaeacanthocephala, and Eoacanthocephala; a fourth class, Polyacanthocephala, has been recently proposed. However, erection of this new class, based on morphological characters, has been controversial. We sequenced the near complete 18S rRNA gene of Polyacanthorhynchus caballeroi (Polyacanthocephala) and Rhadinorhynchus sp. (Palaeacanthocephala); these sequences were aligned with another 21 sequences of acanthocephalans representing the three widely recognized classes of the phylum and with 16 sequences from outgroup taxa. Phylogenetic relationships inferred by maximum-likelihood and maximum-parsimony analyses showed Archiacanthocephala as the most basal group within the phylum, whereas classes Polyacanthocephala + Eoacanthocephala formed a monophyletic clade, with Palaeacanthocephala as its sister group. These results are consistent with the view of Polyacanthocephala representing an independent class within Acanthocephala.     

On the Phylogenetic Position of Rotifera – Have We Come Any Further?

Rotifers are bilateral symmetric animals belonging to Protostomia. The ultrastructure of the rotiferan trophi suggests that they belong to the Gnathifera, and ultrastructural similarities between the integuments and spermatozoa as well as molecular evidence strongly suggest that rotifers and the parasitic acanthocephalans are closely related and form the clade Syndermata. Here we discuss the phylogenetic position of rotifers with regard to the gnathiferan groups. Originally, Gnathifera only included the hermaphroditic Gnathostomulida and the Syndermata. The synapomorphy supporting Gnathifera is the presence of pharyngeal hard parts such as jaws and trophi with similar ultrastructure. The newly discovered Micrognathozoa possesses such jaws and is a strong candidate for inclusion in Gnathifera because their cellular integument also has an apical intracytoplasmic lamina as in Syndermata. But Gnathifera might include other taxa. Potential candidates include the commensalistic Myzostomida and Cycliophora. Traditionally, Myzostomida has been included in the annelids but recent studies regard them either as sister group to the Acanthocephala or Cycliophora. Whether Cycliophora belongs to Gnathifera is still uncertain. Some analyses based on molecular data or total evidence point towards a close relationship between Cycliophora and Syndermata. Other cladistic studies using molecular data, morphological characters or total evidence suggest a sister group relationship between Cycliophora and Entoprocta. More molecular and morphological data and an improved sampling of taxa are obviously needed to elucidate the phylogenetic position of the rotifers and identify which phyla belong to Gnathifera.     

On the evolution and morphology of the rotiferan trophi, with a cladistic analysis of Rotifera

The phylogeny of Rotifera was examined in different computer‐generated cladistic analyses, including Seisonidea, Bdelloidea, Flosculariacea, Collothecacea and all ploimids treated on family level. The analyses were based on a character matrix solely dealing with morphological characters, primarily based on the trophi morphology. Limnognathia maerski (Micrognathozoa), Rastrognathia macrostoma and Gnathostomula paradoxa (Gnathostomulida) were used as outgroups. The cladistic analysis performed by paup produced 288 most parsimonious trees. peewee analyses produced between 140 and 432 trees, depending on the concavity value. The monophyly of Eurotatoria, Monogononta and Ploima was confirmed in all obtained trees. All analyses suggested a division of Ploima into major clades. One clade corresponded to Transversiramida while the other contained all other ploimid taxa and recognized Antrorsiramida as a monophylum. Based on the obtained results a scenario for the trophi evolution is proposed. The analyses suggested that the presence of an incus is synapomorphic for Gnathifera while mallei are synapomorphic for Micrognathozoa and Rotifera. The ancestral rotifer trophi probably resembled those in Harringia (Asplanchnidae).     

Phylogenetic utility of protein (RPB2, β-tubulin) and ribosomal (LSU,SSU) gene sequences in the systematics of Sordariomycetes (Ascomycota,Fungi)

The Sordariomycetes is an important group of fungi whose taxonomic relationships and classification is obscure. There is presently no multi-gene molecular phylogeny that addresses evolutionary relationships among different classes and orders. In this study, phylogenetic analyses with a broad taxon sampling of the Sordariomycetes were conducted to evaluate the utility of four gene regions (LSU rDNA, SSU rDNA, beta-tubulin and RPB2) for inferring evolutionary relationships at different taxonomic ranks. Single and multi-gene genealogies inferred from Bayesian and Maximum Parsimony analyses were compared in individual and combined datasets. At the subclass level, SSU rDNA phylogenies demonstrate their utility as a marker to infer phylogenetic relationships at higher levels. All analyses with SSU rDNA alone, combined LSU rDNA and SSU rDNA, and the combined 28 S rDNA, SSU rDNA and RPB2 datasets resulted in three subclasses: Hypocreomycetidae, Sordariomycetidae and Xylariomycetidae, which correspond well to established morphological classification schemes. At the ordinal level, the best resolved phylogeny was obtained from the combined LSU rDNA and SSU rDNA datasets. Individually, the RPB2 gene dataset resulted in significantly higher number of parsimony informative characters. Our results supported the recent separation of Boliniaceae, Chaetosphaeriaceae and Coniochaetaceae from Sordariales and placement of Coronophorales in Hypocreomycetidae. Microascales was found to be paraphyletic and Ceratocystis is phylogenetically associated to Faurelina, while Microascus and Petriella formed another clade and basal to other members of Halosphaeriales. In addition, the order Lulworthiales does not appear to fit in any of the three subclasses. Congruence between morphological and molecular classification schemes is discussed.