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A new species of Cubozoa found in an aquarium at Hagenbecks Tierpark (Zoo), Hamburg, Germany, is described herein as Carybdea morandinii. The species is distinguished from all known cnidarians in the anatomy of its polyp stage. The gastric cavity of the cubopolyp is divided horizontally into two chambers by a shutter-lens-like diaphragm. Metamorphosis was total and resulted in a single, four-tentacled medusa as in other known cubozoans. Both polyp and medusa stages bear zooxanthellae, which seemed important in the metamorphic process.

The early life stages of the cubomedusa Alatina cf. moseri from Osprey Reef (North Queensland, Australia) and Waikiki (Oahu, Hawaii) were studied using laboratory-based culturing conditions. Spawning populations from both regions were observed with reliable periodicity allowing polyp cultures from these locations to be collected and established under laboratory conditions. The polyps of this species were successfully reared from spawning adults. Polyps of Alatina cf. moseri were cultured at temperatures of 23–28°C, developed up to 19 tentacles and reached up to 1.70 mm in height. The balloon-shaped hypostomes possessed 4 well-defined lips. The polyps increased their numbers by means of formation of either sedentary polyp buds or creeping-polyp buds, which attached after 2–3 days. Metamorphosis occurred at temperatures of 25–28°C. Development of polyps and medusae were achieved for the first time within the genus Alatina and allowed comparisons of early life history between these and other species of the Carybdeida families. The metamorphosis and young medusa of this genus showed characters that differed distinctly from those noted for other Carybdeida species, but are very similar to the one described from Puerto Rico by Arneson and Cutress in 1976 for Alatina sp. (named by them Carybdea alata). Based on this evidence, the discrepancies in original specimen descriptions and the previous genetic comparisons, we support the suggestion that the two previously described species of Alatina from Australia and Hawaii (Alatina mordens and Alatina moseri) appear to represent artificial taxonomic units and may in fact be the same as the original Carybdea alata species named from Puerto Rico. Further taxonomic studies are desperately needed in order to clarify the various species and description discrepancies that exist within this newly proposed genus.

While records of Carybdea marsupialis in the literature suggest a worldwide distribution of this species, the validity of some of these records has been questioned recently, as has the validity of some nominal Carybdea species. We inspected material of all known species of Carybdea from multiple locations (i.e. Spain, Algeria, Tunisia, Puerto Rico, California, Hawaii, Australia, South Africa, and Japan) using morphological and genetic tools to differentiate Carybdea species as well as understand their evolutionary relationships. We observed morphological differences between adult medusae of Mediterranean and Caribbean C. marsupialis; the most obvious differences were the structure of the phacellae, the structure of the pedalial canal knee bend, and the number and structure of the velarial canals. The characters of the adult Mediterranean specimens agree with the description provided by Claus (1878) for individuals of C. marsupialis from the Adriatic Sea (Italy); specimens from the Caribbean (Puerto Rico) agreed with the description of C. xaymacana by Conant (1897). Significant differences between both species were also observed in the newly released medusa stage. Further, we resolved a discord about the undefined polyp culture originating from Puerto Rico that was long considered Carybdea marsupialis but should be referred to as C. xaymacana. Although C. marsupialis is currently considered the only species of Cubozoa to occur in the Mediterranean, specimens collected in Algeria and Tunisia suggest that species of Alatinidae may also be present in the Mediterranean. Our investigations indicate that Carybdea spp. are more restricted in their geographical distribution than has been recognized historically. These findings confirm that Carybdea arborifera Maas, 1897 from Hawaii, Carybdea branchi, Gershwin & Gibbons, 2009 from South Africa, Carybdea brevipedalia Kishinouye, 1891 from Japan, Carybdea confusa Straehler-Pohl, Matsumoto & Acevedo, 2017 from California, Carybdea marsupialis Linnaeus, 1758 from the European Mediterranean Sea, Carybdea rastonii Haacke, 1886 from South Australia, and Carybdea xaymacana, Conant, 1897 from the Caribbean Sea are valid names representing distinct species, rather than synonyms. A taxonomic key for all valid species is provided, and a neotype for C. marsupialis is designated.

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Phacellophora camtschatica has long been assigned to the semaeostome scyphozoan family Ulmaridae. Early stages (scyphistomae, strobilae, ephyrae, postephyrae, and young medusae) of the species were compared with those of several other semaeostomes currently assigned to Ulmaridae, Pelagiidae, and Cyaneidae. Juveniles of P. camtschatica did not strictly conform with characters of those of any of these families, and appeared intermediate between Cyaneidae and Ulmaridae. A new family, Phacellophoridae, is proposed to accommodate P. camtschatica.

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