Cryptic diversity in the leptothecate genera Laodicea and Tiaropsis (Cnidaria: Hydrozoa)

Although they are an ecologically and economically important group of animals, hydrozoans are understudied because of their difficult identification due to their small size and fragility. Hydrozoans as a group show a great diversity in life strategies, and often include both a polyp and a medusa stage in their life cycle, which complicates their taxonomy because both stages may be needed for a correct identification. For the two leptothecate hydrozoan genera Laodicea (Family Laodiceidae) and Tiaropsis (Family Tiaropsidae), the polyp stage is very small and easy to overlook, while the medusa stage is conspicuous and relatively straightforward to identify, at least to genus level. Only one species of each of these genera is believed to occur in Norwegian waters, Laodicea undulata (Forbes &Goodsir, 1853) and Tiaropsis multicirrata (M. Sars, 1835), but preliminary data suggest that the diversity of these taxa in the region is higher than previously thought. In this study, I used DNA barcoding and different molecular species delimitation methods (based on mitochondrial markers 16S and COI and the nuclear marker ITS) in combination with a detailed morphological analysis of both the hydroid and medusa stages to assess the species diversity of the genera Laodicea and Tiaropsis in Norway. Based on molecular evidence, Laodicea undulatais shown to comprise two molecularly distinct Norwegian clades, which appear not to be sister species. Specimens morphologically identified as T. multicirrata split up into three distinct clades in Norway according to the evaluated molecular markers, indicating cryptic diversity in Tiaropsis for the studied region. For both Tiaropsis and Laodicea, the results suggest that the observed clades correspond to undescribed species, but further work is necessary to place them in a broader phylogenetic perspective and to identify any potential morphological characters that define them.Master's Thesis in BiologyBIO399MAMN-BIOMAMN-HAVS