The role of the isolation of the marginal seas during the Pleistocene in the genetic structure of black sea bream Acanthopagrus schlegelii (Bleeker, 1854) in the coastal waters of Japan

The black sea bream Acanthopagrus schlegelii (Bleeker, 1854) is a commercially important species in Japanese waters. Assessing its population structure is essential to ensure its sustainability. In the Northwestern Pacific, historical glacial and interglacial periods during the Pleistocene have shaped the population structure of many coastal marine fishes. However, whether these events affected the population of black sea bream remains unknown. To test this hypothesis and to assess the population structure of black sea bream, we used 1,046 sequences of the mitochondrial control region from individuals collected throughout almost the entire Japanese coastal waters and combined them with 118 sequences from populations distributed in other marginal seas of the Northwestern Pacific Ocean. As in other coastal marine fish with similar distribution, we also found evidence that the glacial refugia on the marginal seas prompted the formation of three lineages in black sea bream. These lineages present signatures of population growth that coincided with the interglacial periods of the Pleistocene. While the origin of Lineages B and C remains unclear, the higher relative frequency of Lineage A in the southernmost location suggests its origin in the South China Sea. The non-significant pairwise ΦST and AMOVA of Japanese populations and the presence of these three lineages mixed in Japanese waters; strongly suggest that these lineages are homogenized in both the Sea of Japan and the Pacific Ocean. Our results indicate that the black sea bream should be managed as a single stock in Japan until the strength of connectivity in contemporary populations is further addressed using non-coding nuclear markers.

A new species of the genus Opisa Boeck, 1876 (Crustacea, Amphipoda, Opisidae) and a new record for Opisa takafuminakanoi from the East Sea, South Korea

Two species of the opisid genus Opisa have been collected from the East Sea of South Korea, one of them described as Opisa parvimanasp. nov.. The new species, O. parvimanasp. nov. is similar to O. odontochela; however, it can be clearly distinguished from this species because it has 12 blunt robust setae in the palm of gnathopod 1. The other collected species, Opisa takafuminakanoi Narahara-Nakano, Kakui & Tomikawa, 2016 is previously known from Japanese waters (southeast of Akkeshi Bay, Hokkaido). Both species are illustrated and compared to related species. A key to Opisa species is also provided.

Two new deep-sea species of the genus Henricia (Asteroidea: Spinulosida: Echinasteridae) from Japanese waters

Two new deep-sea Henricia species, Henricia margarethae n. sp. and Henricia fragilis n. sp. are described from Sagami Bay and the Ogasawara Islands in Japan. The two new species show an affinity with eight congeners in having multiple furrow spines and abactinal papular areas which are larger than surrounding plates. The two species described herein are characterized by the arrangement of abactinal pseudopaxillae, the arrangement of abactinal papulae, the shape and arrangement of abactinal spines, the length of intermarginal and ventrolateral series, and the armament of superomarginal, inferomarginal, and adambulacral plates.

Redescription of a poorly known upogebiid mud shrimp Gebiacantha acanthochela (Sakai, 1967) and description of a new species of the genus from the Ryukyu Islands, Japan (Decapoda: Gebiidea)

Two species of the upogebiida mud shrimp genus Gebiacantha Ngoc-Ho, 1989, currently represented by 19 described species, are reported from the Ryukyu Islands, Japan. The first, G. acanthochela (Sakai, 1967), is redescribed in detail based on two female specimens from Amami Islands the second discovered since the original description, enabling better assessment of its diagnostic characters. The second, G. fortispinata n. sp., is described on the basis of a single female holotype from Okinawa Island. It appears closest to G. multispinosa Ngoc-Ho, 1994, known with certainty only from New Caledonia, but the proportionally narrower telson with a more deeply notched posterior margin and the distally unarmed pereopod 3 merus distinguish the new species from G. multispinosa. Three species of Gebiacantha, including G. sagamiensis Komai, 2017, are now known from Japanese waters.