Deltamysis holmquistae Bowman & Orsi 1992

Deltamysis holmquistae Bowman & Orsi, 1992 Figs 2, 3, 4 Material examined. North Sea Canal • 1 ♂ ad. with BL 3.4 mm (most thoracopods broken, on slides); Spaarnwoude, loc. code NVO-SW; 52.4367°N, 4.7057°E; 16 Oct. 2023; T. van Haaren leg.; canal-km 9.5, brackish water, shallow (<1 m), sandy bottom, pond net; sample code 2023 EASC 00024 • 1 ♀ ad., 3.7 mm, with empty marsupium, in 2 parts, 1 ♀ subad., 3.8 mm (in vial); canal-km 11, Nauerna, loc. code NZK- 11 - O; 52.4306°N, 4.7368°E; 4 Oct. 2023; R. Vlierboom and S. Honcoop leg.; depth 4 m, boxcorer; sample code 2023 EASC 00003.03 • 1 ♀ ad., 3.8 mm, with empty marsupium, 1 ♂ ad., 3.1 mm, 1 ♀ subad., 3.4 mm, 1 imm., 2.8 mm, in 2 parts (in vial); canal-km 6, Velzen, loc. code NZK- 06 - O; 52.4541°N, 4.6749°E; 5 Oct. 2023; R. Vlierboom and S. Honcoop leg.; depth 6 m, van Veen-grab; sample code 2023 EASC 00001.03. Note. The present specimens fit well to the morphological scheme first published by Bowman and Orsi (1992) and revised by Scripter et al. (2020) and Daneliya (2023). Cornea dorsoventrally compressed by a factor of 1.2–1.5. Exopod of maxilla (Fig. 3 E) with 2–4 barbed setae on distal half of lateral margin, proximal half bare. Statoliths composed of fluorite. Figs 2, 3 provide the essential details for determination at species level. In addition, a dichotomous textual key to the four here acknowledged species of the genus Deltamysis Bowman & Orsi, 1992, is given below. Distribution. Bowman and Orsi (1992) first described this species from the San Joaquin Estuary at the coast of California. Later the species was found in shallow mixoeuhaline to anhaline waters of Texas, Florida, and Australia (Scripter et al. 2020; Daneliya 2023). From their redescription based on Florida and Texas materials, Scripter et al. (2020) concluded that the mysid Kochimysis pillaii Panampunnayil & Biju, 2007, from the SW-coast of India is to be considered a junior subjective synonym of D. holmquistae. The published records of D. holmquistae together with the present records from the E-Atlantic fit together to a circumtropical distribution between 37°S and 52°N (Fig. 4). Potential regions of origin of this invasive species are considered in the ‘ Discussion’.