A new species, Gammarus baengnyeongensis sp. nov., belonging to the family Gammaridae Leach, 1814 was collected from the Baengnyeongdo and Daecheongdo islands in South Korea. This new species is characterized by the flagellum of antenna 2 with calceoli, and the length ratio of outer ramus to inner ramus of uropod 3. Descriptions of diagnostic characteristics of the species are provided in the text. We performed statistical analysis to confirm the significance of morphological differences of interspecies. Additionally, we compare the new species to related species by the partial sequence of the mitochondrial cytochrome c oxidase subunit 1 (CO1) gene. Genetic distances between the new species and closely related species rated from 29.1–40.8%, which highly supports Gammarus baengnyeongensis sp. nov. as a valid species. In this study, we add one new Gammarus species in Korean waters.

The genus Protogeton Mayer, 1903 is one of the 89 genera belonging to the family Caprellidae (WoRMS Editorial Board, 2016). Among them, the genus Protogeton is charac terized by having (1) flagellum with 3-5 articles in antenna 2; (2) mandible lacking molar, with uni-or biarticulate palp;(3) pereonites 3-4 with gills; (4) pereopods 3-5 well developed, consisting of 6articulates; and (5) lacking appendages on the abdomen (Arimoto, 1976). This genus is a taxon with only two species; P. incertus Mayer, 1903 andP. inflatus Mayer, 1903, which are distributed in the northern Pacific and Indian Ocean regions. Protogeton incertus is discernible from P. inflatus by the biarticulate mandibular palp and swollen carpus and propodus on pereopod 3 (GuerraGarcía, 2004). The original description of P. incertus by Mayer (1903) was incomplete, with only one illustration for mandibular palp. Later, Arimoto (1980) and GuerraGarcía (2004) redescribed this species; however, the redescriptions were also brief and not supported by detailed illustrations. There fore, this time, we provide full description of Korean Proto geton incertus including illustrations for mouthparts and appendages and a description of the immature male, especial ly with the dimorphic character of pereopod 3. Specimens were collected by light trap from the shallow and sublittoral waters in Korea (Fig.

A new species of the corophiid gammaridean amphipods belonging to the rare genusEocorophiumBousfield & Hoover, 1997 was collected from Korean waters. The new species is fully illustrated and compared with related species. This is the first record of the genusEocorophiumfrom Korea. A key to the species ofEocorophiumis also provided.

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.