Phylogenetics and species delimitation of two hydrozoa (phylum Cnidaria): Turritopsis (McCrady, 1857) and Pennaria (Goldfuss, 1820)

Using a ~ 600 bps fragment of the mitochondrial 16S gene, we reconstruct the phylogenetic history of the species complex Pennaria disticha and of the genus Turritopsis. P. disticha and, within the genus Turritopsis, Turritopsis dohrnii are considered invasive species with a very broad geographical range. We show that the invasive T. dohrnii has reached the Gulf of Mexico (GoM) and Brazil. We heavily sampled the Bocas del Toro region, Panama, where three species of Turritopsis (the invasive T. dohrnii and the endemic T. sp. 1 and T. sp. 4) have been recorded, and found that the invasive T. dohrnii is the most common species, while the endemic species were either very rare (T. sp. 1) or were not found (T. sp. 4). We show that T. dohrnii from Bocas del Toro can revert its life cycle from medusa to polyp, while T. sp. 1 may lack this capability. Finally, we find that in the Maldives, Emirates, and the Red Sea, there are morphologically and genetically distinct Turritopsis lineages. With regard to Pennaria disticha, we analyzed new sequences from Thuwal (Saudi Arabia, Red Sea), Sint Eustatius (the Netherlands, Caribbean), Bocas del Toro (Panama, Caribbean Sea), Bergeggi (Italy, Mediterranean Sea), Tricase (Italy, Mediterranean Sea), Dibba Al-Fujairah (United Arab Emirates, Gulf of Oman), and Galveston (Texas, Gulf of Mexico). We confirm the presence of several clades and putative cryptic species that indicates multiple invasive episodes and undercover a new clade from the Gulf of Oman. Finally, species delimitation analyses recover 2 to 3 clades as separate species within P. disticha, and 7 to 9 species within Turritopsis, with T. lata being a complex of 2–4 cryptic species.