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Ostracod crustaceans are among the most abundant microfossils in the geological record, thanks to their strongly cal- cified shell. Most of the fossils belong to the suborder Cytherocopina, which also has a rich diversity of living species. Unfortunately, many of the living representatives are known only by their shell morphology. Soft body always provides valuable insights into the phylogeny, and sometimes conflicts with currently accepted systematics of this group. We provide a complete description of Coquimba ishizakii Yajima 1978, collected from Jeju Island, South Korea. This is the first report on soft body morphology for the entire genus Coquimba Ohmert 1968, and the first record of this genus from Korea. Its soft body morphology is similar to other representatives of the family Hemicytheridae, where Coquimba currently belongs. After reviewing all records of C. ishizakii, we propose that several of them belong to different species, such as all those from Taiwan (modern and fossil). We also provide 18S rRNA and 28S rRNA sequences for this species, the latter being reported for the first time for the entire family Hemicytheridae [ABSTRACT FROM AUTHOR]

Aim of study: Marine climatic transition zones are boundary areas of major climate zones, here the boundary between the subtropical and temperate zones. They present areas containing high abundance of organisms living at the limit of their physiological tolerance. These marginal populations are particularly sensitive to changes in their environment. As such, marine climatic transition zones are excellent natural playgrounds for climate change-related hypothesis testing, especially with respect to marine habitat response to ocean warming. The marginal biogenic habitats around Jeju Island, South Korea, which lies within the temperate transition zone, have gradually changed from macroalgal-dominated to hard coral-dominated habitats. Understanding the specific abiotic environmental factors that influence the distribution of the marginal populations in temperate transition zones (i.e., species at their occurrence limit) is crucial to predicting and managing temperate zone habitat changes caused by climate change. This study aims to identify the specific abiotic environmental factors that contribute to explaining the current spatial distribution of the declining temperate and expanding subtropical foundation species in Jeju waters. Methods: Coverage and composition of sessile benthic communities were determined by photo-quadrat analysis at two depths (10 m and 15 m) at three sites along the island's south, east, and north coasts in May and November 2022. Divergences in community composition between sites were characterized in light of ten quantitative environmental parameters. Results: Our results show that sessile foundation communities vary significantly at different sites around the island. While the south is defined by high-latitude hard corals, predominately Alveopora japonica, the east is defined by the temperate canopy-forming macroalga Ecklonia cava, and the north is characterized by coralline algae. Winter sea surface temperature, water transparency, nutrient concentration, and water movement were statistically the most impactful environmental factors determining which foundation species constitute each distinct benthic community. Conclusion: This study provides valuable baseline information on the impacts of abiotic environmental factors on marine sessile communities in a temperate transition zone. [ABSTRACT FROM AUTHOR]

The genus Semicytherura Wagner, 1957 has nearly 300 species, is common in shallow and marginal marine habitats, and has a worldwide distribution. It is divided into several species groups, of which the Semicytherura henryhowei Hanai & Ikeya, 1977 group is one of the most frequently recorded in temperate Asia. A previous study indicated that many of its members are actually species complexes, and that several morphotypes could be distinguished by carapace shape and ornamentation. We review these complexes and conclude that the henryhowei group currently contains 29 species, nine of which are undescribed. We also provide an illustrated guide and a key to species, based on newly standardized carapace ridge terminology. This enabled us to describe one new species from the extant (i.e., present-day) sediments in Jeju Island, Korea, S. kiosti sp. nov. We also found one juvenile valve of S. kazahana Yamada, Tsukagoshi & Ikeya, 2005, the first official illustrated record of this species from Korean waters. Our revised spatial and temporal distributions of fossil and extant records from this group provide new insights into trans-Arctic interchange of ostracod fauna from the Late Miocene onwards. [ABSTRACT FROM AUTHOR]

Presented here is an illustrated checklist of benthic marineOstracoda (Crustacea) recorded fromRecent surface sediments of the sub-polar North Atlantic Ocean (SPNA). It presents 142 species (and species groups) belonging to 62 genera from 41 sampling sites collected from the water depths of 144-2749 m. We provide census datawith scanning electron microscope images of representative specimens of most species, aswell as geographical and bathymetrical distributionmaps of selected species and genera. Samples from the Nordic seas (i.e., Greenland Sea, Norwegian Sea), as well as North Atlantic proper waters (i.e., Irminger Sea, Iceland Sea) are included. The bathymetry covers shelf to continental rise surface sediments from the Irminger Basin, the Iceland Basin, the Iceland Plateau, the Denmark Strait, the Faeroe-Shetland Channel, the Iceland-Faeroe Ridge, the Reykjanes Ridge, and the Faeroe Plateau. The data presented here is an important taxonomic and biogeographical baseline of the SPNA benthic ostracod fauna. [ABSTRACT FROM AUTHOR]