﻿First record of the genus Pseudaeginella Mayer, 1890 (Crustacea, Amphipoda, Caprellidae) with a new species from Korean waters

﻿Abstract A new species of the genus Pseudaeginella Mayer, 1890 belonging to the family Caprellidae Leach, 1814 was collected from the South Sea in Korea. Pseudaeginellacarinaspinosasp. nov. is morphologically similar to related congeners belonging to the genera Paradeutella Mayer, 1890 and Pseudaeginella, in having dorsal projections on pereonites, triarticulate mandibular palp, small or absent molar, and uniarticulate pereopods 3 and 4. However, this new species is distinguished from its congeners by the position and size of dorsal projection. This is the first record of Pseudaeginella from the Northwest Pacific region, including Korea, and a key to species of the genus Pseudaeginella is also provided.


Introduction
Caprellids, known as skeleton shrimp, are relatively small marine amphipods that are abundant and important members of the marine benthos.They inhabit a wide variety of substrates such as algae, hydrozoans, bryozoans, sponges, seagrasses, gorgonians, sediment, and other marine invertebrates (Guerra-García 2001;Woods 2009).
In this article, we provide a full description of the new species of Pseudaeginella from Korean waters, with a brief description of the female, focusing on sexually dimorphic characters.So far, 10 genera of caprellids have been recorded in Korean waters (Kim and Lee 1975;Lee 1988;Lee andHong 2009, 2010;Hong et al. 2015;Heo et al. 2016;Shin et al. 2021).Pseudaeginella is newly recorded for the Korean caprellid fauna and is the first record of the genus from the Northwest Pacific region, including Korea.

Material and method
Specimens were collected by SCUBA diving from algae such as Ecklonia sp. and Sargassum sp. in the shallow water areas of Geomun-Island, Namhyeongje-Island, Jeju-Island located off the south coast of Korea (Fig. 1).The specimens were fixed with 95% ethanol and dissected in glycerol on Cobb's aluminum hollow slides.Permanent mounts were made using polyvinyl lactophenol with lignin pink added.Pencil drawing and measurements were performed with the aid of drawing tube, mounted on an SZX 12 stereomicroscope (Olympus, Japan) and a BX 51 interference contrast compound microscope (Olympus, Japan).Line drawings were produced using the program Clip Studio Paint (Celsys, Japan).Type specimens are deposited at the National Institute of Biological Resources (NIBR), Incheon, Korea and the Department of Biological Sciences, Dankook University (DKU), Cheonan, Korea.
Paratype, female (sexually dimorphic characters), NIBRIV0000904522.Body (Figs 2B,5A) 3.4 mm long, generally as in male, but stouter than male, pereonites 3, 4 with rounded brood pouches.Gnathopod 2 (Fig. 5B) similar to that of male, but propodus more rounded than that of male.Abdomen (Fig. 5C) similar to that of male, but with a pair of plumose setae.
Etymology.The species name is derived from the Latin carina (=back) and spinosa (= with spinose projection) with reference to the distinct dorsal spinose projection.

Key to the species of Pseudaeginella
Modified after Iwasa-Arai et al. 2019.

Table 1 .
Comparison of characters of the males of Pseudaeginella species.