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

Newly collected acanthocephalans.

<p>Some species with identical sequence data have been collected from different hosts.</p

Bayesian consensus phylogram for Acanthocephala relationship based on the SSU rDNA data set.

<p>Rotifera is used as outgroup, acanthocephalans are classified as indicated on the right site of the graphic. This tree illustrates the hypothesis that the order Echinorhynchida (blue) and Polymorphida (red) have a paraphyletic arrangement. The branch length scale is the number of substitutions per site.</p

SEM (scanning electron microscope) micrographs of Palaeacanthocephala.

<p>(A) Proboscis of male <i>Rhadinorhynchus pristis</i> from <i>Gempylus serpens</i> (Indonesia, Indian Ocean) armed with regular hooks a and basal hook annulus. (B) Praesoma of female <i>R. lintoni</i> from <i>Selar crumenophthalmus</i> (Hawaii, Pacific) with irregular arrangement of trunk hooks. (C) Praesoma of <i>Gorgorhynchoides golvani</i> from <i>Platycephalus arenarius</i> (Indonesia, Indian Ocean) regular arrangement of surface hooks. (D) Habitus of <i>Serrasentis sagittifer</i> from <i>Platycephalus arenarius</i> (Indonesia, Indian Ocean) with hooks are transformed into strong plates arranged as combs. (E) Habitus of <i>Pomphorhynchus laevis</i> from <i>Platichthys flesus</i> (Baltic Sea) shows any trunk hooks on bulb, neck and trunk. (F) Praesoma of <i>Bolbosoma vasculosum</i> from <i>Lepturacanthus savala</i> (Indonesia, Indian Ocean) formed in the shape of a bulb, and armed with regular hooks which are arranged in two rings. Scale bars: A 400 µm, B, D, F, 200 µm, E 100 µm.</p

Tree statistics for rDNA data set.

<p>Numbers of informative characters, consistency index (CI) and tree length refer to parsimony inference. Proportion of invariable sites (Pinv), shape of gamma distribution (Gd) and –ln Likelihood refer to Maximum Likelihood Inference.</p

Electrophoretic analysis of restriction mapping.

<p>Lane 1 shows the pCR®2.1-TOPO® vector (3923 bp) above, which is cleaved by <i>EcoRI</i> (Invitrogen, Karlsruhe) and below the amplified 18S rRNA gene fragment (1724 bp) with the correct orientation (lane 2 with the incorrect orientation). The controls show the amplified PCR product (lane 3) and vector without insert (lane 4). M: marker λ-EcoRI +HindIII-Marker-Mix 3 (Fermentas, St. Leon-Rot) 1 µg.</p