Medusozoan genomes inform the evolution of the jellyfish body plan

Cnidarians are astonishingly diverse in body form and lifestyle, including the presence of a jellyfish stage in medusozoans and its absence in anthozoans. Here, we sequence the genomes of Aurelia aurita (a scyphozoan) and Morbakka virulenta (a cubozoan) to understand the molecular mechanisms responsible for the origin of the jellyfish body plan. We show that the magnitude of genetic differences between the two jellyfish types is equivalent, on average, to the level of genetic differences between humans and sea urchins in the bilaterian lineage. About one-third of Aurelia genes with jellyfish-specific expression have no matches in the genomes of the coral and sea anemone, indicating that the polyp-to-jellyfish transition requires a combination of conserved and novel, medusozoa-specific genes. While no genomic region is specifically associated with the ability to produce a jellyfish stage, the arrangement of genes involved in the development of a nematocyte-a phylum-specific cell type-is highly structured and conserved in cnidarian genomes; thus, it represents a phylotypic gene cluster

FIGURE 7. Maximum-likelihood tree for 11 in Scolionema sanshin sp. n., a new species (Hydrozoa, Limnomedusae, Olindiidae) from the Ryukyu Archipelago, southern Japan

FIGURE 7. Maximum-likelihood tree for 11 limnomedusan taxa based on the nuclear 18 S rDNA data set. Scale bars indicate branch length in substitutions per site. Nodal support values are presented as the ML bootstrap value; only values> 50 % are shoWn

Octorhopalona saltatrix, a New Genus and Species (Hydrozoa, Anthoathecata) from Japanese Waters

Approximately 300 species of cnidarian jellyfish have been reported in Japanese waters. However, many specimens remain unidentified. In this study, taxonomic investigations, including morphological observations and molecular 16S phylogenetic analyses, were conducted on unknown specimens collected off Oarai, Sagami Bay, and Tosa Bay, Japan. The specimens have the following morphological characteristics: distinct peaks in jelly above the base of the manubrium, a red band on the manubrium, and cylindrical marginal bulbs, each with an abaxial ocellus that is common to the family Halimedusidae. However, the specimens can be distinguished from other Halimedusidae species by their eight radial canals, eight tentacles with numerous stalked nematocyst knobs, and eight nematocyst tracks on the exumbrella. Moreover, molecular phylogenetic analyses revealed that the Kimura two-parameter distance between the specimens and other Halimedusa species was 0.066–0.099, which is considered to represent intergeneric variability. Based on this result, we described it as a new species and established a new genus for taxonomic stabilization. We also emended the diagnostic characters of the family Halimedusidae owing to the establishment of the new genus. Halimedusidae comprises five species in four genera. This paper provides taxonomic keys for the identification of species in the family Halimedusidae

Caltsacoryne setouchiensis (Hydrozoa, Anthoathecata) a new genus and species of hydrozoan jellyfish from Japan

Toshino, Sho, Hamatsu, Yoshimi, Uchida, Hiroaki (2021): Caltsacoryne setouchiensis (Hydrozoa, Anthoathecata) a new genus and species of hydrozoan jellyfish from Japan. Zootaxa 5032 (1): 87-103, DOI: https://doi.org/10.11646/zootaxa.5032.1.

Olindias deigo sp. nov., a new species (Hydrozoa, Trachylinae, Limnomedusae) from the Ryukyu Archipelago, southern Japan

A new hydromedusa belonging to the order Limnomedusae is reported from the Ryukyu Archipelago, southern Japan. Olindias deigo sp. nov. can be distinguished from other Olindiidae species by the number and color of tentacles. Mature medusae of O. deigo sp. nov. were collected to observe the life history, including polyp (hydroid) and medusa formation. A comparative table of the primary diagnostic characters of the genus is provided

Meteorona kishinouyei, a new family, genus and species (Cnidaria, Cubozoa, Chirodropida) from Japanese Waters

A new family, genus and species of cubozoan box jellyfish belonging to the order Chirodropida is reported from the eastern Japan. Meteorona kishinouyei gen. et sp. n. possesses the following unique morphological characters with respect to other known species in the Chirodropida: having one tentacle per scalpel-like unbranched pedalium and slightly raised unbranched gastric saccules. A comparative table of the primary diagnostic characters of genus and order in the Chirodropida is given. The order Chirodropida is redefined. The family Chiropsellidae is established. Discussion is provided on the implications for these findings on our current understanding of Cubozoan systematics

Olindias deigo sp. nov., a new species (Hydrozoa, Trachylinae, Limnomedusae) from the Ryukyu Archipelago, southern Japan

A new hydromedusa belonging to the order Limnomedusae is reported from the Ryukyu Archipelago, southern Japan. Olindias deigo sp. nov. can be distinguished from other Olindiidae species by the number and color of tentacles. Mature medusae of O. deigo sp. nov. were collected to observe the life history, including polyp (hydroid) and medusa formation. A comparative table of the primary diagnostic characters of the genus is provided