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The genus Nyctiphanes (Malacostraca, Euphausiacea) comprises four neritic species that display antitropical geographic distribution in the Pacific ( N. simplex and N. australis) and Atlantic ( N. couchii and N. capensis) Oceans. We studied the origin of this distribution applying methods for phylogenetic reconstruction and molecular dating of nodes using a Bayesian MCMC analysis and the DNA sequence information contained in mtDNA 16S rDNA and cytochrome oxidase (COI). We tested hypotheses of vicariance by contrasting the time estimates of cladogenesis with the onset of the major barriers to ocean circulation. It was estimated that Nyctiphanes originated in the Pacific Ocean during the Miocene, with a lower limit of 18 miilion years ago (Mya). An Atlantic–Pacific cladogenic event (95% HPD 3.2–9.6) took place after the closure of the Tethyan Sea, suggesting that dispersal occurred from the Indo-Pacific, most likely via southern Africa. Similarly, the antitropical distribution pattern observed in the eastern Atlantic Ocean likely resulted from recent Pliocene–Pleistocene (95% HPD 1.0–4.97) northward dispersal from the southern hemisphere. Our results imply that dispersal appears to have had a significant role to play in the evolution of this group. [ABSTRACT FROM AUTHOR]

Background: The Octopus vulgaris species complex consists of numerous morphologically similar but genetically distinct species. The current publicly available mitogenome of this species has been generated from a specimen collected from Tsukiji Fish Market, Tokyo, Japan. Octopus from the northwestern Pacific Ocean are now considered to be a separate species, Octopus sinensis. For this reason, we hypothesised that the current record of O. vulgaris was sequenced from a specimen of O. sinensis. Here, we sequenced the first complete mitogenome of a specimen of Octopus vulgaris sensu stricto that was collected from the species' confirmed distribution areas in northeastern Atlantic., Methods and Results: The complete mitogenome was assembled de novo and annotated using 250 bp paired-end sequences. A single circular contig 15,655 bp in length with a mean read coverage of 1089 reads was reconstructed. The annotation pipeline identified 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNA) and two ribosomal RNAs. A maximum likelihood phylogenetic tree recovered the assembled mitogenome as the sister taxon of a monophyletic group comprising O. sinensis and the previously published mitogenome of "O. vulgaris" from Japan. This confirms that the latter was a Japanese specimen of O. sinensis., Conclusion: The mitogenome sequenced here is the first to be published for Octopus vulgaris sensu stricto. It represents an important first step in genetics-informed research on the evolution, conservation, and management of this commercially important species., (© 2023. The Author(s).)

Sequence data derived from four markers (the nuclear RP1 and Aldolase and the mitochondrial 16S rRNA and cytochrome b genes) were used to determine the phylogenetic relationships among 32 species belonging to the genus Hippocampus. There were marked differences in the rate of evolution among these gene fragments, with Aldolase evolving the slowest and the mtDNA cytochrome b gene the fastest. The RP1 gene recovered the highest number of nodes supported by >70% bootstrap values from parsimony analysis and >95% posterior probabilities from Bayesian inference. The combined analysis based on 2317 nucleotides resulted in the most robust phylogeny. A distinct phylogenetic split was identified between the pygmy seahorse, Hippocampus bargibanti, and a clade including all other species. Three species from the western Pacific Ocean included in our study, namely H. bargibanti, H. breviceps, and H. abdominalis occupy basal positions in the phylogeny. This and the high species richness in the region suggests that the genus evolved somewhere in the West Pacific. There is also fairly strong molecular support for the remaining species being subdivided into three main evolutionary lineages: two West Pacific clades and a clade of species present in both the Indo-Pacific and the Atlantic Ocean. The phylogeny obtained herein suggests at least two independent colonization events of the Atlantic Ocean, once before the closure of the Tethyan seaway, and once afterwards.