Abstract: Knowledge on benthic diatom taxonomy and hence biodiversity from Arctic locations is rare, though the few existing analyses address morphological characteristics only. Morphological treatment is a time-consuming process and just allows the taxonomic identification of a low sample volume. In contrast, molecular sequencing is a faster and universally applicable approach, and also has the potential for refined analyses. Unfortunately, a lot of molecular information in databases is not trustable, and often existing genetic data do not fit together with morphological aspects. Therefore, the main goal of our study was for the first time to combine both morphological features and DNA information on benthic Arctic diatoms. In a first step, we studied the morphology of 26 strains from the Rostock Culture Collection of Arctic diatoms via light and electron microscopies. Secondly, we addressed their molecular taxonomy by sequencing the DNA barcode 18S V4 and the chloroplast marker rbcL. As a result, we could identify five species. Seven of the altogether twelve taxa could not be attributed to any known species, because listed sequences and morphology did not fit together. From these, three species were described as new to science here. Although the studied strains represent only a minor fraction of the diatom flora of Svalbard, this study is a first milestone in coupling morphological and molecular data of benthic diatoms in such high latitudes. By making these data available online, they contribute to a taxonomic reference library for Arctic benthic diatoms and are available for comparative studies.

Abstract: Eusiroidea is one of the 20 amphipod superfamilies that were erected to subdivide the very large and controversial suborder Gammaridea. Yet, the definition of the superfamily is not based on synapomorphies, but on a combination of diagnostic phenetic similarities that hold more or less consistently across families. Moreover, many of the characters used to define eusiroid families are suspected to show convergent evolution. The current classification of the Eusiroidea may therefore not reflect evolutionary relationships accurately. Here, we present a molecular phylogenetic re-analysis of the Eusiroidea based on a comparison of 18S and 28S rDNA sequences of 73 species, representing 47 genera and 16 families that potentially belong to the superfamily. The results suggest that at least species belonging to 14 of these traditional families would be part of a eusiroid clade, increasing by more than twofold the species and generic richness of the group. However, most of the eusiroid families surveyed do not appear monophyletic. Finally, the analyses show that several important morphological characteristics, traditionally used in eusiroid taxonomy, are homoplastic.