A selection from Stockholm University publication database
A multigene molecular assessment reveals deep divergence in the phylogeny of Nemertodermatida
Inga Meyer-Wachsmuth, Ulf Jondelius.
Here we present a comprehensive phylogeny of Nemertodermatida, a taxon of microscopic marine worms, based for the first on molecular marker with consideration of morphological characters. Our dataset comprises three nuclear genes and most nominal and putative species including recently described cryptic species; only species of the genus Ascoparia could not be obtained. We show that the two families of Nemertodermatida, Ascopariidae and Nemertodermatidae, are retrieved as separate clusters, although not in all analyses as sister groups. We also validate sequences published before 2013 against our dataset; some sequences are shown to be chimeric and have falsified prior hypotheses about nemertodermatid phylogeny, other sequences should be assigned new names. We also show that the genus Nemertoderma needs revision.
Phylogeny of Chaetonotidae (Gastrotricha) inferred from nuclear and mitochondrial genes
Tobias Kånneby, M. Antonio Todaro, Ulf Jondelius.
Chaetonotidae is the largest family within Gastrotricha with almost 400 nominal species, represented in both freshwater and marine habitats. The group is probably non-monophyletic and suffers from a troubled taxonomy. Current classification is to a great extent based on shape and distribution of cuticular structures, characters that are highly variable. We present the most densely sampled molecular study so far where 17 out of 31 genera belonging to Chaetonotida are represented. Bayesian and maximum likelihood approaches based on 18S rDNA, 28S rDNA and COI mtDNA are used to reconstruct relationships within Chaetonotidae. The use of cuticular structures for supra-specific classification within the group is evaluated and the question of dispersal between marine and freshwater habitats is addressed. Moreover the subgeneric classification of Chaetonotus is tested in a phylogenetic context. Our results show high support for a clade containing Dasydytidae nested within Chaetonotidae. Within this clade only 3 genera are monophyletic following current classification. Genera containing both marine and freshwater species never form monophyletic clades and group with other species according to habitat. Marine members of Aspidiophorus appear to be the sister group of all other Chaetonotidae and Dasydytidae, indicating a marine origin of the clade. Halichaetonotus and marine Heterolepidoderma form a monophyletic group in a sister group relationship to freshwater species, pointing towards a secondary invasion to marine environments of these taxa. Our study shows the problems of current classification based on cuticular structures, characters that show homoplasy for deeper relationships.
Interrelationships of Nemertodermatida
2016. Inga Meyer-Wachsmuth, Ulf Jondelius. Organisms Diversity & Evolution 16 (1), 73-84Article
Nemertodermatida is a small taxon of microscopic marine worms, which were originally classified within Platyhelminthes. Today they are hypothesized to be either an early bilaterian lineage or the sister group to Ambulacraria within Deuterostomia. These two hypotheses indicate widely diverging evolutionary histories in this largely neglected group. Here, we analyse the phylogeny of Nemertodermatida using nucleotide sequences from the ribosomal LSU and SSU genes and the protein coding Histone 3 gene. All currently known species except Ascoparia neglecta and Ascoparia secunda were included in the study in addition to several yet undescribed species. Ascopariidae and Nemertodermatidae are retrieved as separate clades, although not in all analyses as sister groups. Non-monophyly of Nemertodermatida was rejected by the Approximately Unbiased test. Nemertodermatid nucleotide sequences deposited in Genbank before 2013 were validated against our dataset; some of them are shown to be chimeric implying falsification of prior hypotheses about nemertodermatid phylogeny: other sequences should be assigned new names. We also show that the genus Nemertoderma needs revision.