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.     

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.     

Phylogenetic relationships among Syndermata inferred from nuclear and mitochondrial gene sequences

Phylogenetic relationships among Syndermata have been extensively debated, mainly because the sister-group of the Acanthocephala has not yet been clearly identified from analyses of morphological and molecular data. Here we conduct phylogenetic analyses on samples from the 4 classes of Acanthocephala (Archiacanthocephala, Eoacanthocephala, Polyacanthocephala, and Palaeacanthocephala) and the 3 Rotifera classes (Bdelloidea, Monogononta, and Seisonidea). We do so using small-subunit (SSU) and large-subunit (LSU) ribosomal DNA and cytochrome c oxidase subunit 1 (cox 1) sequences. These nuclear and mitochondrial DNA sequences were obtained for 27 acanthocephalans, 9 rotifers, and representatives of 6 phyla that were used as outgroups. Maximum parsimony (MP), maximum likelihood (ML), and Bayesian analyses were conducted on the nuclear rDNA(SSU+LSU) and the combined sequence dataset(SSU+LSU+cox 1 genes). Phylogenetic analyses of the combined rDNA and cox 1 data uniformly provided strong support for a clade including rotifers plus acanthocephalans (Syndermata). Strong support was also found for monophyly of Acanthocephala in analyses of the combined dataset or rDNA sequences alone. Within the Acanthocephala the monophyletic grouping of the representatives of each class was strongly supported. Our results depicted Archiacanthocephala as the sister-group to the remaining acanthocephalans. Analyses of the combined dataset recovered a sister-group relationship between Acanthocephala and Bdelloidea by parsimony, likelihood, and Bayesian methods. Support for this clade was generally strong. Alternative topologies that depicted a different rotifer sister-group of Acanthocephala (or monophyly of Rotifera) were significantly worse. In this paraphyletic assemblage of rotifers, the relative positions of Seisonidea and Monogononta to the clade Bdelloidea+Acanthocephala were inconsistent among trees based on different inference methods. These results indicate that Bdelloidea is the free-living sister-group to acanthocephalans, which should prove key for comparative investigations of the morphological, molecular, and ecological changes accompanying the evolution of parasitism.     

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.     

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.     

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.     

Mitogenomic phylogeny of Acanthocephala reveals novel Class relationships

The Acanthocephala is a phylum of obligate endoparasitic animals comprising four classes (Archiacanthocephala, Palaeacanthocephala, Eoacanthocephala and Polyacanthocephala), although the phylogenetic interrelationships of these classes still remains unresolved. To investigate phylogenetic relationships of major acanthocephalan groups, we characterized the complete mitochondrial genome sequences of two palaeacanthocephalan species Centrorhynchus aluconis and Prosthorhynchus transversus (representing two different families of the order Polymorphida), and Polyacanthorhynchus caballeroi (the first mitogenomic representative of the class Polyacanthocephala) and used these new sequences for phylogenetic analyses, along with 32 platyzoan mtDNAs, including 10 additional acanthocephalans. Phylogenetic analyses using concatenated amino acid sequences for 12 protein‐coding genes with maximum likelihood and Bayesian inference methods supported monophyly of Acanthocephala. Within the phylum, Archiacanthocephala was positioned as the sister to the clade containing all three other acanthocephalan classes, with the polyacanthocephalan species P. caballeroi nested within Eoacanthocephala. This result contradicts morphology‐based classification systems that treated polyacanthorhynchids as one of the palaeacanthocephalan families, and instead suggests Polyacanthocephala is a member of Eoacanthocephala. Within the Palaeacanthocephala, Polymorphida monophyly was strongly supported and this is inconsistent with nuclear rDNA‐based molecular hypotheses that suggest non‐monophyly.     

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.     

Phylogeny of the Acanthocephala based on morphological characters

Only four previous studies of relationships among acanthocephalans have included cladistic analyses, and knowledge of the phylogeny of the group has not kept pace with that of other taxa. The purpose of this study is to provide a more comprehensive analysis of the phylogenetic relationships among members of the phylum Acanthocephala using morphological characters. The most appropriate outgroups are those that share a common early cell-cleavage pattern (polar placement of centrioles), such as the Rotifera, rather than the Priapulida (meridional placement of centrioles) to provide character polarity based on common ancestry rather than a general similarity likely due to convergence of body shapes. The phylogeny of 22 species of the Acanthocephala was evaluated based on 138 binary and multistate characters derived from comparative morphological and ontogenetic studies. Three assumptions of cement gland structure were tested: (i) the plesiomorphic type of cement glands in the Rotifera, as the sister group, is undetermined; (ii) non-syncytial cement glands are plesiomorphic; and (iii) syncytial cement glands are plesiomorphic. The results were used to test an early move of Tegorhynchus pectinarius to Koronacantha and to evaluate the relationship between Tegorhynchus and Illiosentis. Analysis of the data-set for each of these assumptions of cement gland structure produced the same single most parsimonious tree topology. Using Assumptions i and ii for the cement glands, the trees were the same length (length = 404 steps, CI = 0.545, CIX = 0.517, HI = 0.455, HIX = 0.483, RI = 0.670, RC = 0.365). Using Assumption iii, the tree was three steps longer (length = 408 steps, CI = 0.539, CIX = 0.512, HI = 0.461, HIX = 0.488, RI = 0.665, RC = 0.359). The tree indicates that the Palaeacanthocephala and Eoacanthocephala both are monophyletic and are sister taxa. The members of the Archiacanthocephala are basal to the other two clades, but do not themselves form a clade. The results provide strong support for the Palaeacanthocephala and the Eoacanthocephala and the hypothesis that the Eoacanthocephala is the most primitive group is not supported. Little support for the Archiacanthocephala as a monophyletic group was provided by the analysis. Support is provided for the recognition of Tegorhynchus and Illiosentis as distinct taxa, as well as the transfer of T. pectinarius to Koronacantha.     

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.     

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.     

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.     

Molecular evidence for Acanthocephala as a subtaxon of Rotifera

Rotifers are free-living animals usually smaller than 1 mm that possess a characteristic wheel organ. Acanthocephalans (thorny-headed worms) are larger endoparasitic animals that use vertebrates and arthropods to complete their life cycle. The taxa Acanthocephala and Rotifera are considered separate phyla, often within the taxon Aschelminthes. We have reexamined the relationship between Rotifera and Acanthocephala using 18S rRNA gene sequences. Our results conclusively show that Acanthocephala is the sister group of the rotifer class Bdelloidea. Rotifera was nonmonophyletic in all molecular analyses, which supports the hypothesis that the Acanthocephala represent a taxon within the phylum Rotifera and not a separate phylum. These results agree with a previous cladistic study of morphological characters. Correspondence to: J.R. Garey     

Molecular phylogeny of the Acanthocephala (class Palaeacanthocephala) with a paraphyletic assemblage of the orders Polymorphida and Echinorhynchida

Acanthocephalans are attractive candidates as model organisms for studying the ecology and co-evolutionary history of parasitic life cycles in the marine ecosystem. Adding to earlier molecular analyses of this taxon, a total of 36 acanthocephalans belonging to the classes Archiacanthocephala (3 species), Eoacanthocephala (3 species), Palaeacanthocephala (29 species), Polyacanthocephala (1 species) and Rotifera as outgroup (3 species) were analyzed by using Bayesian Inference and Maximum Likelihood analyses of nuclear 18S rDNA sequence. This data set included three re-collected and six newly collected taxa, Bolbosoma vasculosum from Lepturacanthus savala, Filisoma rizalinum from Scatophagus argus, Rhadinorhynchus pristis from Gempylus serpens, R. lintoni from Selar crumenophthalmus, Serrasentis sagittifer from Johnius coitor, and Southwellina hispida from Epinephelus coioides, representing 5 new host and 3 new locality records. The resulting trees suggest a paraphyletic arrangement of the Echinorhynchida and Polymorphida inside the Palaeacanthocephala. This questions the placement of the genera Serrasentis and Gorgorhynchoides within the Echinorhynchida and not the Polymorphida, necessitating further insights into the systematic position of these taxa based on morphology.     

Phylogenetic relationships within phylum Rotifera: orders and genus Notholca

We investigated evolutionary relationships among orders in phylum Rotifera and among species in genus Notholca (Rotifera) by computing parsimonious cladograms. All of the most-parsimonious cladograms generated for the ordinal level confirm the view that class Monogononta, superclass Eurotatoria, and phylum Rotifera are monophyletic. Species within the genus Notholca were separated into six groups (clades), but some species have been defined based on highly variable characters not reliably studied using cladistics. Therefore, phenetic studies are warranted, especially for species possessing caudal processes.     

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.     

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.     

Performance of 18S rDNA helix E23 for phylogenetic relationships within and between the Rotifera-Acanthocephala clades

The species diversity of the phylum Rotifera has been largely studied on the basis of morphological characters. However, cladistic relationships within this group are poorly resolved due to extensive homoplasy in morphological traits, substantial phenotypic plasticity and a poor fossil record. We undertook this study to determine if a phylogeny based on partial 18S rDNA, which included the helix E23 of 18S rDNA sequence, was concordant with established taxonomic relationships within the order Ploimida (class: Monogononta). We also estimated the level of polymorphism within clones and populations of Ploimida 'species'. Finally, we included the Cycliophora Symbion pandora as outgroup and the variable helix E23 region to examine the influence of their signal on the evolutionary relationships among Acanthocephala, Bdelloidea and Ploimida. Phylogenetic reconstruction was performed using maximum parsimony, neighbour joining and maximum likelihood methods. We found 1) that morphologically similar Ploimida 'species' show vastly different 18S E23 rDNA sequences; 2) inclusion of the helix E23 of 18S rDNA and its secondary structure analysis results in better resolution of family level relationships within the Ploimida; 3) an impact of Symbion pandora as an outgroup with inclusion of the helix E23 on the relationships between the Rotifera and the Acanthocephala; and 4) partial incongruence and differential substitution rate between conserved region and helix E23 region of the 18S rDNA gene depending on the taxomic group studied.     

Ultrastructure and overall organization of ligament sac, uterine bell, uterus and vagina in Paratenuisentis ambiguus (Acanthocephala, Eoacanthocephala) – the character evolution within the Acanthocephala

As an adaptation to their endoparasitic lifestyle, Acanthocephala (Palaeacanthocephala, Eoacanthocephala, Polyacanthocephala, Archiacanthocephala) have evolved a highly specialized reproductive system. Most of our present knowledge of the efferent duct system of the female is based on palaeacanthocephalan and archiacanthocephalan representatives. In order to provide a basis for further elucidating the phylogenetic relationships within the Acanthocephala, we herein describe ultrastructure and overall organization of the ligament sac and efferent duct system in females of Paratenuisentis ambiguus (Eoacanthocephala, Neoechinorhynchida). Only one ligament sac was found. The uterine bell consists of two contractile binucleate syncytia (bell wall syncytium, lateral pocket syncytium), two pairs of contractile cells (lappet cells, uterine bell retractors) and three pairs of noncontractile cells (median cells). The contractile uterus bears four nuclei. The vagina is composed of a syncytial epithelium (four nuclei) and two binucleate sphincters. A comparison of the present findings with literature data leads to the following conclusions: except for the uterine bell retractors, the uterine bell components found in P. ambiguus can be assumed to be autapomorphies for the Acanthocephala. The sheathing syncytium and median dorsal cell belong to the basal pattern (sensu ground pattern) of a palaeacanthocephalan subclade termed the Echinorhynchus‐group in the present study. The median oviduct syncytium and paired uterine bell retractors can be assumed to be basal pattern characteristics of the Archiacanthocephala and Neoechinorhynchida, respectively. The study includes a tabular survey of terminological synonyms used in the literature.