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.