Data from: Morphological and molecular diagnostic species characters of Staurozoa (Cnidaria) collected on the coast of Helgoland (German Bight, North Sea)

Scientific knowledge and records on staurozoans are limited probably because of their inconspicuous life habit and the small number of specialists for this taxon. To increase the awareness for Staurozoa, we identified morphological and molecular features of the three staurozoan species Haliclystus tenuis Kishinouye, 1910, Haliclystus auricula Clark, 1863, and Craterolophus convolvulus (Johnston, 1835) collected on the coast of the island Helgoland to evaluate their suitability as diagnostic characters. Useful macromorphological diagnostic features were the patterns of white spots of nematocysts and internal arm structures, whereas tentacle and gonad follicle numbers showed high intraspecific variations. Morphometric measurements on photographs of living specimens provided reliable data for interspecific comparisons. Comprehensive nematocyst analyses revealed interspecific shape differences of isorhizas and three types of rhopaloids, indicating that the staurozoan cnidome is more diverse than previously assumed. However, the taxonomic value of nematocyst analyses in Staurozoa remains unclear because comprehensive data is still lacking for most species. Comparative molecular genetic sequence analyses of mitochondrial 16S and COI and nuclear 18S ribosomal DNA identified the three species and confirmed their morphological identification. In comparison to published data, our analyses indicate similarities between H. auricula and Haliclystus antarcticus Pfeffer, 1889. Proteomic fingerprinting by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) differentiated all three species, suggesting that this technique could provide an alternative rapid identification method for staurozoans