An updated phylogeny,biogeography, and PhyloCode-based classification of Cornaceae based on three sets of genomic data

Premise

A major goal of systematic biology is to uncover the evolutionary history of organisms and translate that knowledge into stable classification systems. Here, we integrate three sets of genome-wide data to resolve phylogenetic relationships in Cornaceae (containing only Cornus s.l.), reconstruct the biogeographic history of the clade, and provide a revised classification using the PhyloCode to stabilize names for this taxonomically controversial group.

Methods

We conducted phylogenetic analyses using 312 single-copy nuclear genes and 70 plastid genes from Angiosperms353 Hyb-Seq, plus numerous loci from RAD-Seq. We integrated fossils using morphological data and produced a dated phylogeny for biogeographical analysis.

Results

A well-resolved, strongly supported, comprehensive phylogeny was obtained. Biogeographic analyses support an origin and rapid diversification of Cornus into four morphologically distinct major clades in the Northern Hemisphere (with an eastern Asian ancestor) during the late Cretaceous. Dispersal into Africa from eastern Asia likely occurred along the Tethys Seaway during the Paleogene, whereas dispersal into South America likely occurred during the Neogene. Diversification within the northern hemisphere likely involved repeated independent colonization of new areas during the Paleogene and Neogene along the Bering Land Bridge, the North Atlantic Land Bridge, and the Tethys Seaway. Thirteen strongly supported clades were named following rules of the PhyloCode.

Conclusions

Our study provides an example of integrating genomic and morphological data to produce a robust, explicit species phylogeny that includes fossil taxa, which we translate into an updated classification scheme using the PhyloCode to stabilize names.     

Resolution of the Hylobates phylogeny: congruence of mitochondrial D-loop sequences with molecular, behavioral, and morphological data sets

Gibbons of the genus Hylobates likely speciated very rapidly following isolation by rising sea levels during the Pleistocene. We sequenced the hypervariable region I (HV-I) of the mitochondrial D-loop to reconstruct the phylogeny of this group. Although the results clearly supported monophyly of each of the six species, the relationships among them were not clearly resolved by these data alone. A homogeneity test against published data sets of a coding mitochondrial locus (ND3-ND4 region), behavioral characters (vocalizations), and morphological traits (including skeletal and soft tissue anatomy) revealed no significant incongruence, and combining them resulted in a phylogenetic tree with much stronger support. The Kloss's gibbon (H. klossii), long considered a primitive taxon based on morphology, shares many molecular and vocal characteristics with the Javan gibbon (H. moloch), and appear as the most recently derived species. The northernmost species (H. lar and H. pileatus) are the most basal taxa. These data suggest that ancestral gibbons radiated from north to south. Unlike other markers, the HV-I region can accurately identify members of different gibbon species much like a DNA barcode, with potential applications to conservation.     

Viburnum phylogeny based on combined molecular data: implications for taxonomy and biogeography

We investigated Viburnum phylogeny using separate and combined analyses of DNA sequence data from two chloroplast and three nuclear loci. Separate analyses of nuclear and chloroplast data sets resulted in gene trees that were generally congruent with one another and with trees from two previous analyses. Our gene trees do differ in the position of section Pseudotinus, as well as in species relationships within sections Pseudotinus and Lentago. However, tests for incongruence indicate that differences between the nuclear and chloroplast data are not significant. Furthermore, gene trees from combined analyses were highly similar to those found in separate analyses, suggesting that these localized differences do not affect other parts of the tree. Our analyses provide convincing support for numerous relationships, although there is still uncertainty at the base of the tree. To facilitate future study, we propose informal names for 12 well-supported species groups, as well as for several higher-level clades. We also discuss the biogeographic implications of our phylogeny, focusing on repeated, although apparently temporally incongruent, patterns of disjunction between the Old and New Worlds.     

基于rDNA-ITS序列的散斑壳属系统发育学初步研究

对散斑壳属Lophodermium 22个种的40个rDNA-ITS序列进行分析,研究了该属种间系统发育关系。对以简约法构建的系统进化树分析表明,散斑壳属种间亲缘关系与其寄主有很大的相关性,针叶树和阔叶树上的散斑壳可能是亲缘关系较远的两大类群,寄主和产地的不同导致了L.agathidis、L.australe和L.conigenum等种内遗传变异。同时,子囊果的开口机构和唇细胞的有无及特征在种水平分类上具有重要意义,而rDNA-ITS序列系统学分析并不能证实子囊果埋生位置在散斑壳属分类上的重要性。     

A molecular phylogeny of the Canidae based on six nuclear loci

We have reconstructed the phylogenetic relationships of 23 species in the dog family, Canidae, using DNA sequence data from six nuclear loci. Individual gene trees were generated with maximum parsimony (MP) and maximum likelihood (ML) analysis. In general, these individual gene trees were not well resolved, but several identical groupings were supported by more than one locus. Phylogenetic analysis with a data set combining the six nuclear loci using MP, ML, and Bayesian approaches produced a more resolved tree that agreed with previously published mitochondrial trees in finding three well-defined clades, including the red fox-like canids, the South American foxes, and the wolf-like canids. In addition, the nuclear data set provides novel indel support for several previously inferred clades. Differences between trees derived from the nuclear data and those from the mitochondrial data include the grouping of the bush dog and maned wolf into a clade with the South American foxes, the grouping of the side-striped jackal (Canis adustus) and black-backed jackal (Canis mesomelas) and the grouping of the bat-eared fox (Otocyon megalotis) with the raccoon dog (Nycteruetes procyonoides). We also analyzed the combined nuclear + mitochondrial tree. Many nodes that were strongly supported in the nuclear tree or the mitochondrial tree remained strongly supported in the nuclear + mitochondrial tree. Relationships within the clades containing the red fox-like canids and South American canids are well resolved, whereas the relationships among the wolf-like canids remain largely undetermined. The lack of resolution within the wolf-like canids may be due to their recent divergence and insufficient time for the accumulation of phylogenetically informative signal.     

Ascidian molecular phylogeny inferred from mtDNA data with emphasis on the Aplousobranchiata

We explored the usefulness of mtDNA data in assessing phylogenetic relationships within the Ascidiacea. Although ascidians are a crucial group in studies of deuterostome evolution and the origin of chordates, little molecular work has been done to ascertain the evolutionary relationships within the class, and in the studies performed to date the key group Aplousobranchiata has not been adequately represented. We present a phylogenetic analysis based on mitochondrial cytochrome c oxidase subunit I (COI) sequences of 37 ascidian species, mainly Aplousobranchiata (26 species). Our data retrieve the main groups of ascidians, although Phlebobranchiata appeared paraphyletic in some analyses. Aplousobranch ascidians consistently appeared as a derived group, suggesting that their simple branchial structure is not a pleisiomorphic feature. Relationships between the main groups of ascidians were not conclusively determined, the sister group of Aplousobranchiata was the Stolidobranchiata or the Phlebobranchiata, depending on the analysis. Therefore, our data could not confirm an Enterogona clade (Aplousobranchiata+Phlebobranchiata). All of the tree topologies confirmed previous ideas, based on morphological and biochemical characters, suggesting that Cionidae and Diazonidae are members of the clade Aplousobranchiata, with Cionidae occupying a basal position within them in our analyses. Within the Aplousobranchiata, we found some stable clades that provide new data on the evolutionary relationships within this large group of ascidians, and that may prompt a re-evaluation of some morphological characters.     

A molecular phylogeny of anseriformes based on mitochondrial DNA analysis

To study the phylogenetic relationships among Anseriformes, sequences for the complete mitochondrial control region (CR) were determined from 45 waterfowl representing 24 genera, i.e., half of the existing genera. To confirm the results based on CR analysis we also analyzed representative species based on two mitochondrial protein-coding genes, cytochrome b (cytb) and NADH dehydrogenase subunit 2 (ND2). These data allowed us to construct a robust phylogeny of the Anseriformes and to compare it with existing phylogenies based on morphological or molecular data. Chauna and Dendrocygna were identified as early offshoots of the Anseriformes. All the remaining taxa fell into two clades that correspond to the two subfamilies Anatinae and Anserinae. Within Anserinae Branta and Anser cluster together, whereas Coscoroba, Cygnus, and Cereopsis form a relatively weak clade with Cygnus diverging first. Five clades are clearly recognizable among Anatinae: (i) the Anatini with Anas and Lophonetta; (ii) the Aythyini with Aythya and Netta; (iii) the Cairinini with Cairina and Aix; (iv) the Mergini with Mergus, Bucephala, Melanitta, Callonetta, Somateria, and Clangula, and (v) the Tadornini with Tadorna, Chloephaga, and Alopochen. The Tadornini diverged early on from the Anatinae; then the Mergini and a large group that comprises the Anatini, Aythyini, Cairinini, and two isolated genera, Chenonetta and Marmaronetta, diverged. The phylogeny obtained with the control region appears more robust than the one obtained with mitochondrial protein-coding genes such as ND2 and cytb. This suggests that the CR is a powerful tool for bird phylogeny, not only at a small scale (i.e., relationships between species) but also at the family level. Whereas morphological analysis effectively resolved the split between Anatinae and Anserinae and the existence of some of the clades, the precise composition of the clades are different when morphological and molecular data are compared.     

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.     

The phylogeny of the austral grass subfamily Danthonioideae: Evidence from multiple data sets

The grass subfamily Danthonioideae is one of the smaller in the family. We utilize DNA sequence data from three chloroplast regions (trnL, rpoC2 and rbcL) and one nuclear region (Internal Transcribed Spacer; ITS) both singly and in combination to elucidate the relationships of the genera in the subfamily. The topology retrieved by the ITS region is not congruent with that of the plastid data, but this conflict is not strongly supported. Nine well-supported clades are retrieved by all data sets. The relationships at the base of the subfamily are clearly established, comprising a series of three clades of Merxmuellera species. The earliest diverging clade probably does not belong in Danthonioideae. The other two clades are centered in the tropical African mountains and Cape mountains respectively. A clade of predominantly North and South American Danthonia species as well as D. archboldii from New Guinea is retrieved, but the African and Asian species of Danthonia are related to African species of Merxmuellera, thus rendering Danthonia polyphyletic. The relationships of the Danthonia clade remain equivocal, as do those of the two Cortaderia clades, the Pseudopentameris and Rytidosperma clades. Paseka Mafa was tragically killed in a vehicle accident in July 2001. This paper includes information he collected during the course of his MSc in Systematics and Biodiversity Science at the University of Cape Town.     

Molecular phylogeny of the hominoids: inferences from multiple independent DNA sequence data sets

Consensus on the evolutionary relationships of humans, chimpanzees, and gorillas has not been reached, despite the existence of a number of DNA sequence data sets relating to the phylogeny, partly because not all gene trees from these data sets agree. However, given the well-known phenomenon of gene tree-species tree mismatch, agreement among gene trees is not expected. A majority of gene trees from available DNA sequence data support one hypothesis, but is this evidence sufficient for statistical confidence in the majority hypothesis? All available DNA sequence data sets showing phylogenetic resolution among the hominoids are grouped according to genetic linkage of their corresponding genes to form independent data sets. Of the 14 independent data sets defined in this way, 11 support a human- chimpanzee clade, 2 support a chimpanzee-gorilla clade, and one supports a human-gorilla clade. The hypothesis of a trichotomous speciation event leading to Homo; Pan, and Gorilla can be firmly rejected on the basis of this data set distribution. The multiple-locus test (Wu 1991), which evaluates hypotheses using gene tree-species tree mismatch probabilities in a likelihood ratio test, favors the phylogeny with a Homo-Pan clade and rejects the other alternatives with a P value of 0.002. When the probabilities are modified to reflect effective population size differences among different types of genetic loci, the observed data set distribution is even more likely under the Homo-Pan clade hypothesis. Maximum-likelihood estimates for the time between successive hominoid divergences are in the range of 300,000-2,800,000 years, based on a reasonable range of estimates for long-term hominoid effective population size and for generation time. The implication of the multiple-locus test is that existing DNA sequence data sets provide overwhelming and sufficient support for a human-chimpanzee clade: no additional DNA data sets need to be generated for the purpose of estimating hominoid phylogeny. Because DNA hybridization evidence (Caccone and Powell 1989) also supports a Homo-Pan clade, the problem of hominoid phylogeny can be confidently considered solved.      

Towards unification of national vegetation classifications: A comparison of two methods for analysis of large data sets

Abstract. In European phytosociology, national classifications of corresponding vegetation types show considerable differences even between neighbouring countries. Therefore, the European Vegetation Survey project urgently needs numerical classification methods for large data sets that are able to produce compatible classifications using data sets from different countries. We tested the ability of two methods, TWINSPAN and COCKTAIL, to produce similar classifications of wet meadows (Calthion, incl. Filipendulenion) for Germany (7909 relevés) and the Czech Republic (1287 relevés) in this respect. In TWINSPAN, the indicator ordination option was used for classification of two national data sets, and the extracted assignment criteria (indicator species) were applied crosswise from one to the other national data set. Although the data sets presumably contained similar community types, TWINSPAN revealed almost no correspondence between the groups derived from the proper classification of the national data set and the groups defined by the assignment criteria taken from the other national data set. The reason is probably the difference in structure between the national data sets, which is a typical, but hardly avoidable, feature of any pair of phytosociological data sets. As a result, the first axis of the correspondence analysis, and consequently the first TWINSPAN division, are associated with different environmental gradients; the difference in the first division is transferred and multiplied further down the hierarchy. COCKTAIL is a method which produces relevé groups on the basis of statistically formed species groups. The user determines the starting points for the formation of species groups, and groups already found in one data set can be tested for existence in the other data set. The correspondence between the national classifications produced by COCKTAIL was fairly good. For some relevé groups, the lack of correspondence to groups in the other national data set could be explained by the absence of the corresponding vegetation types in one of the countries, rather than by methodological problems.     

A phylogeny of ranid frogs (Anura: Ranoidea: Ranidae), based on a simultaneous analysis of morphological and molecular data

During the last two decades, major taxonomic rearrangements were instituted in the anuran family Ranidae. Most of these changes were not based on phylogenetic analysis, and many are controversial. Addressing the phylogeny of Ranidae requires broader taxon sampling within the superfamily Ranoidea, the phylogenetic relationships and higher classification of which are also in a state of flux. No comprehensive attempt has yet been made to reconstruct ranid phylogeny using both morphological and molecular data. In the present contribution, data from 178 organismal characters were collated for 74 exemplar species representing the families Arthroleptidae, Hemisotidae, Hyperoliidae, Mantellidae Microhylidae, Petropedetidae, Rhacophoridae, Sooglossidae, and most subfamilies of Ranidae. These were combined with ～1 kb of DNA sequence from the mitochondrial 12S rDNA and 16S rDNA gene regions in a simultaneous parsimony analysis with direct optimization. Results support the classification of Hemisus with the brevicipitine microhylids, confirm that Arthroleptidae (and its two component subfamilies Astylosterninae and Arthroleptinae) are monophyletic, and advocate the recognition of Leptopelidae. Monophyly of Ranidae is compromised by recognition of Petropedetidae, Rhacophoridae and Mantellidae, which should be recognized as subfamilies of Ranidae at present. Furthermore, Petropedetidae was found to be grossly paraphyletic, comprising three clades which are all considered separate subfamilies of Ranidae, i.e., Petropedetinae, Phrynobatrachinae and Cacosterninae. Three well defined subfamilies of Ranidae were consistently retrieved as monophyletic in a sensitivity analysis, i.e., Tomopterninae, Ptychadeninae and Pyxicephalinae. However, Ptychadeninae and Pyxicephalinae were embedded in Raninae and Dicroglossinae, respectively. Ceratobatrachinae is removed from Dicroglossinae. Dicroglossinae is synonymized with Pyxicephalinae. A new subfamily Strongylopinae is proposed. Raninae should be conservatively treated as a “metataxon” (sensu Ford and Cannatella, 1993 ) until such time as it is fully revised. Tomopterninae is removed from synonymy with Cacosterninae. Morphological synapomorphies are reported for major monophyletic clades retrieved in the simultaneous analysis with equal weights. The present study found that many Old World clades appear to contain both African and Asian taxa, contrary to the findings of some recent biogeographical analyses. This study demonstrates the value of broad taxonomic sampling in ranid phylogeny, and highlights the immense contribution that can be made from detailed morphological data. © The Willi Hennig Society 2005.     

A molecular phylogeny of East African Amytta (Orthoptera: Tettigoniidae,Meconematinae) with data on their cytogenetics

This is the first study to address the molecular phylogeny of East African Meconematinae. We used DNA sequence data from the three genes cytochrome oxidase subunit I (COI ), 16S rRNA and histone H3 to reconstruct the relationships within the genus Amytta using Bayesian Inference and maximum likelihood. We included 45 individuals representing 19 Meconematinae taxa from Africa, Europe and Australia, and three outgroup species to explore taxonomic limits at different levels. Members of the genus Amytta belong to three related lineages within Meconematinae. Species of Amytta were found to be monophyletic with Meconema and Phlugidia as sister groups. The molecular results are in accordance with previous morphological and ecological studies. Chromosome numbers and the type of sex determination systems found in Amytta agrees with the three lineages also found in the phylogenetic tree. We conclude that the radiation of Amytta species is geological young. Biogeographical patterns caused by climatic fluctuations of the past seen also in other nonrelated Orthoptera taxa such as the coptacrine genus Parepistaurus are the drivers of biodiversity in the area.     

Phylogeny and historical biogeography of leafhopper subfamily Iassinae (Hemiptera: Cicadellidae) with a revised tribal classification based on morphological and molecular data

Phylogenetic relationships among major lineages of the leafhopper subfamily Iassinae were explored by analysing a dataset of 91 discrete morphological characters and DNA sequence data from nuclear 28S rDNA and histone H3 genes and mitochondrial 12S rDNA. Bayesian, maximum‐likelihood and maximum parsimony analyses yielded similar tree topologies that were well resolved with strong branch support except at the base of the tree, resulting in equivocal support for inclusion of Bythoniini as a tribe of Iassinae but strong support for the monophyly of Iassinae (excluding Bythoniini) and most previously recognized iassine tribes. Divergence times for recovered nodes were estimated using a Bayesian relaxed clock method with two fossil calibration points. The results suggest that the deepest divergences coincided with Gondwanan vicariant events but that more recent divergences resulted from long‐range dispersal and colonization. Biogeographical analyses suggest that the group most likely has a Neotropical origin. The following changes to the taxonomic classification are proposed: establishment of three new tribes, Batracomorphini trib.n. (based on type genus Batracomorphus Lewis), Hoplojassini trib.n. (based on type genus Hoplojassus Dietrich and including one other South American genus), Lipokrisnini trib.n. (based on type genus Lipokrisna Freytag and including two other endemic Caribbean genera); Krisnini is redefined to include only the Old World genera Krisna and Gessius; Iassini is redefined to include only the type genus and four endemic Afrotropical genera; Bascarrhinus Fowler and Platyhynna Berg, recently treated as genera incertae sedis, are placed in Hyalojassini; Thalattoscopus Kirkaldy is added to the previously monobasic tribe Trocnadini. Iassinae now includes 12 tribes, all of which appear to be monophyletic. Revised morphological diagnoses of the subfamily and each of the included tribes are provided and a key to tribes is also given. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:41295B68‐2DAB‐4C4F‐B260‐F7C054922173 .     

A molecular phylogeny of four endangered Madagascar tortoises based on MtDNA sequences

Four of the five tortoise species in Madagascar, Pyxis arachnoides, P. planicauda, Geochelone radiata, and G. yniphora, are endemic and on the verge of extinction. Their phylogenetic relationships remain controversial and unresolved. Here we address the phylogeny of this group using DNA sequences for the 12S and 16S rDNA and cyt b genes in mitochondrial DNA. As outgroups we used two species of Geochelone, pardalis (mainland Africa) and nigra (Galápagos), as well as a more distant North American tortoise, Gopherus polyphemus. We conclude that the two Pyxis species are sister taxa and are imbedded in the genus Geochelone, rendering this latter genus paraphyletic. There is moderate support for the sister status of the two Madagascar Geochelone and for the monophyletic origin of all four endemics, suggesting a single colonization of the island. The separation of Madagascar from other land masses (90-165 mya) predates the origin of the endemic tortoises (estimated to be 14-22 mya). This suggests founding by rafting, a process known to have occurred with other tortoises. The derived morphological divergence of the Pyxis species in a relatively short period of time (13-20 my) stands in contrast to the notoriously slow rate of morphological evolution in most lineages of Chelonia.     

A molecular phylogeny of bryophytes based on nucleotide sequences of the mitochondrialnad5 gene

In contrast to animals, the slowly evolving mitochondrial nucleotide sequences of plants appear well suited to investigate phylogenetic relations between old taxonomic groups. Analysis ofnad5 gene sequences in 47 bryophytes, the living representatives of very early land plants, confirm this assessment. Statistically reliable phylogenetic trees are obtained with different mathematical approaches. A group I intron sequence conserved in thenad5 gene of all 30 mosses and 15 liverworts investigated supports a sister group relationship of the two classes. The intron sequence adds phylogenetic information for fine resolution on top of the conserved exon sequences down to the level of classically defined orders or families, respectively. This intron is not present in the hornwortsAnthoceros husnotii andA. punctatus. The results allow statements on diverging taxonomic interpretations and support the monophyly of the liverworts, mosses, Jungermanniidae, Marchantiidae and Bryidae, and allow recognition of subclasses like Hypnanae and Dicrananae. Among the mosses, the derived orders (subclass Bryidae) are confidently set apart from the Sphagnales, Andreaeales, Polytrichales and Tetraphidales with Buxbaumiales occupying a mediating position. Among the liverworts, full support is found for the classic separation of simple (jungermanniid) and complex thalloid (marchantiid) species with a strikingly low mitochondrial sequence divergence among the latter.     

A molecular phylogeny for the Drosophila melanogaster subgroup and the problem of polymorphism data

Drosophila melanogaster belongs to a closely related group of eight species collectively known as the melanogaster subgroup; all are native to sub-Saharan Africa and islands off the east coast of Africa. The phylogenetic relationships of most species in this subgroup have been well documented; however, the three most closely related species, D. simulans, D. sechellia, and D. mauritiana, have remained problematic from a phylogenetic standpoint as no data set has unambiguously resolved them. We present new DNA sequence data on the nullo and Serendipity-alpha genes and combine them with all available nuclear DNA sequence data; the total data encompass 12 genes and the ITS of rDNA. A methodological problem arose because nine of the genes had information on intraspecific polymorphisms in at least one species. We explored the effect of inclusion/exclusion of polymorphic sites and found that it had very little effect on phylogenetic inferences, due largely to the fact that 82% of polymorphisms are autapomorphies (unique to one species). We have also reanalyzed our previous DNA-DNA hybridization data with a bootstrap procedure. The combined sequence data set and the DNA-DNA hybridization data strongly support the sister status of the two island species, D. sechellia and D. mauritiana. This at least partially resolves what had been a paradox of parallel evolution in these two species.      

The phylogeny of rotifers: molecular,ultrastructural and behavioural data

This work discusses the nature and significance of molecular, ultrastructural, and behavioural characters that can be used in phylogenetic analyses of rotifers.Recent molecular research has demonstrated the presence of very small amounts of 4-hydroxyproline in rotifers, probably arising from acetyl-cholinesterase or glycoproteins. Thus, rotifers appear to be the first known Metazoa without collagen.Ultrastructural work also has made some interesting discoveries. (1) The myelinic cuticle of the integument and pharynx of gastrotrichs is present in the pharynx of at least two rotifers (Philodina and Brachionus) and some Annelida. (2) The intracytoplasmic lamina (IL) of the syncytial ingestive integument of Acanthocephala is similar to the IL of the syncytial stomach of Bdelloidea. (3) The fibrous terminal web of primitive epidermal ciliated cells may have evolved in the skeletal IL of the syncytial, aciliated integument of rotifers. (4) Using the ultrastructural features of the skeletal, IL of the integument, I derived two possible dendograms of rotifer evolution. (5) These models and other ultrastructural data predict that Bdelloidea should be separated from Monogononta, while Seison has several characters which suggest that it should be more closely aligned to the Monogononta than previously proposed.Molecular and ultrastructural data suggest that rotifers are primitive Metazoa, probably derived by neoteny from ancestral, ciliated larvae. Finally, I argue that information on sensory organs and the behaviour of rotifers may offer unique insights into the evolution of the phylum.