509Wallberg, A., Curini-Galletti, M., Ahmadzadeh, A. & Jondelius, U. (2007). Dismissal of Acoelomorpha: Acoela and Nemertodermatida are separate early bilaterian clades. -Zoologica Scripta , 36 , 509-523. We used new 18S and 28S rRNA sequences analysed with parsimony, maximum likelihood and Bayesian methods of phylogenetic reconstruction to show that Nemertodermatida, generally classified as the sister group of Acoela within the recently proposed Phylum Acoelomorpha, are a separate basal bilaterian lineage. We used several analytical approaches to control for possible long branch attraction (LBA) artefacts in our results. Parsimony and the model based phylogenetic reconstruction methods that incorporate 'corrections' for substitution rate heterogenities yielded concordant results. When putative long branch taxa were experimentally removed the resulting topologies were consistent with our total evidence analysis. Deletion of fast-evolving nucleotide sites decreased resolution and clade support, but did not support a topology conflicting with the total evidence analysis. Establishment of Acoela and Nemertodermatida as two early lineages facilitates reconstruction of ancestral bilaterian features. The ancestor of extant Bilateria was a small, benthic direct developer without coelom or a planktonic larval stage. The previously proposed Phylum Acoelomorpha is dismissed as paraphyletic.

The Childiidae sensu Do¨rjes 1968 comprises the acoel worms characterized by a cone-shaped penis with muscular or sclerotized elements. Based on differences in body-wall musculature arrangement, Hooge (2001) recently restricted the family to the genus Childia Graff, 1910 and placed the remaining genera to his new family Actinoposthiidae Hooge 2001. This rearrangement has been questioned (Raikova et al. 2004). We reconstructed the phylogeny of the Childiidae sensu Do¨rjes 1968 by means of a total evidence analysis including Histone H3, 28S rDNA and new 18S rDNA sequences, as well as 50 morphological characters. New characters of the muscular system and copulatory organs discovered through confocal laser scanning microscopy of phalloidin-stained specimens are included in the phylogenetic analysis. A total of 12 taxa (nine ingroup and three outgroup) were used in the parsimony analysis of the 18S data set, which was aligned with different parameters for a sensitivity analysis, and the combined data set (18S + 28S + H3 + morphology). Incongruence in the node support of the groups among the four partitions was very low in the total evidence tree; except for the H3 partition. The conflict observed in the H3 partition is likely due to large homoplasy observed in the synonymous alternatives at both first and third codon positions. All data partitions demonstrated that Actinoposthia beklemischevi Mamkaev 1965, and the newly defined taxon Childiidae (comprising Childia and Paraphanostoma Westblad 1942) are not close relatives. The monophyly of Childia and Paraphanostoma is strongly supported by both the 18S and 28S data partitions. Our study also reveals additional apomorphies uniting Childia with Paraphanostoma from body-wall musculature, statocyst muscles and male copulatory organ. Muscular system, statocyst muscles, male copulatory organ and nervous system characters proved to be the best characters for taxonomic delimitations of subtaxa within the Childiidae, whereas the seminal bursa (a frequently used character in the taxonomy of Acoela) was highly homoplastic. We also described the body-wall musculature of six Paraphanostoma species, which is characterized by the reversed arrangement of the longitudinal and circular muscle layers, and by the absence of diagonal muscles on the ventral side of the body and the presence of two types of diagonal muscles on the dorsal side. Childia groenlandica (Levinsen, 1879) is nested among the Paraphanostoma species in our total evidence tree, so we synonymize Paraphanostoma with Childia; all former members of Paraphanostoma are transferred to Childia.

Evolution of lineage diversification through time is an active area of research where much progress has been made in the last decade. Contrary to the situation in animals and plants little is known about how diversification rates have evolved in most major groups of protist. This is mainly due to uncertainty about phylogenetic relationships, scarcity of the protist fossil record and the unknown diversity within these lineages. We have analyzed the evolutionary history of the supergroup Amoebozoa over the last 1000 million years using molecular dating and species number estimates. After an origin in the marine environment we have dated the colonization of terrestrial habitats by three distinct lineages of Amoebozoa: Dictyostelia, Myxogastria and Arcellinida. The common ancestor of the two sister taxa, Dictyostelia and Myxogastria, appears to have existed before the colonization of land by plants. In contrast Arcellinida seems to have diversify in synchrony with land plant radiation, and more specifically with that of mosses. Detection of acceleration of diversification rates in Myxogastria and Arcellinida points to a co-evolution within the terrestrial habitats, where land plants and the amoebozoans may have interacted during the evolution of these new ecosystems.

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