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.

目前关于十字水母纲（Staurozoa）的科学认知与记录较为匮乏，这大概率与其隐蔽的生活习性以及该类群的专业研究人员数量稀少有关。为提升学界对十字水母纲的关注，我们对在黑尔戈兰岛（Helgoland）沿岸采集的3种十字水母物种——细海壶水母（Haliclystus tenuis Kishinouye, 1910）、耳海壶水母（Haliclystus auricula Clark, 1863）以及旋凹钵水母（Craterolophus convolvulus (Johnston, 1835)）——的形态与分子特征展开鉴定，以评估其作为分类鉴定特征的适用性。
具有实用价值的大形态学鉴定特征包括刺细胞（nematocysts）白斑分布模式与内部腕部结构，而触手与生殖腺滤泡的数量则表现出较高的种内变异。对活体标本照片进行的形态测量数据可用于可靠的种间比较。全面的刺胞组（cnidome）分析揭示了等刺丝囊（isorhizas）与3种棍刺丝囊（rhopaloids）的种间形态差异，表明十字水母纲的刺胞组多样性远超此前的认知。然而，由于多数十字水母物种的相关数据仍存在缺失，刺胞分析在十字水母分类学中的应用价值仍有待明确。
针对线粒体16S、COI基因以及核18S核糖体DNA的比较分子遗传学序列分析成功鉴定了上述3个物种，并验证了其形态学鉴定结果。与已发表数据对比后，我们的分析显示耳海壶水母（Haliclystus auricula）与南极海壶水母（Haliclystus antarcticus Pfeffer, 1889）存在较高的序列相似性。
通过基质辅助激光解吸电离飞行时间质谱（matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, MALDI-TOF MS）获得的蛋白质组指纹图谱可区分这3个物种，提示该技术可作为十字水母物种快速鉴定的替代方法。