Brittle stars (Echinodermata: Ophiuroidea) comprise over 2,000 species, all of which inhabit marine environments and can be abundant in the deep sea. Morphological plasticity in number and shape of skeletal parts, as well as variable colors, can complicate correct species identification. Consequently, DNA sequence analysis can play an important role in species identification. In this study we compared the genetic variability of the mitochondrial cytochrome c subunit I gene (COI) and the nuclear small subunit ribosomal DNA (SSU, 18S rDNA) to morphological identification of 66 specimens of 11 species collected from the North Atlantic in Icelandic waters. Also two species delimitation tools, Automatic Barcode Gap Discovery (ABGD) and General Mixed Yule Coalescence Method (GMYC) were performed to test species hypotheses. The analysis of both gene fragments was successful to discriminate between species and provided new insights into some morphological species hypothesis. Although less divergent than COI, it is helpful to use the SSU region as a complementary fragment to the barcoding gene.
The end−Permian mass extinction constituted a major event in the history of crinoids. It led to the demise of the major Paleozoic crinoid groups including cladids, disparids, flexibles and camerates. It is widely accepted that a single lineage, derived from a late Paleozoic cladid ancestor (Ampelocrinidae), survived this mass extinction. Holocrinid crinoids ( Holocrinus , Holocrinida) along with recently described genus Baudicrinus (Encrinida), the only crinoid groups known from the Early Tria ssic, are considered the stem groups for the post−Paleozoic monophyletic subc lass Articulata. Here, we report preliminary data on unexpectedly diverse crinoid faunas comprisin g at least four orders from the Lower Triassic (Induan and Olenekian) of Svalbard, extending their stratigraphic ranges deeper into the early Mesozoic. These findings strongly imply that the recovery of crinoids in the aftermath of the end−Permian extinction began much earlier at higher palaeolatitudes than in the central Tethys.