Sanyuania cuneata Zhao & Whatley, 1992 (Ostracoda, Cytheroidea, Cytherideidae) from Japan: morphology, distribution and environmental significance

Abstract. Sanyuania cuneata Zhao & Whatley, 1992 was reported initially from Late Pleistocene core samples from the northern part of the Yellow Sea and Recent sediments collected from supra tidal pools (17 practical salinity unit (psu)) in Xiangshangang Bay, East China Sea (Zhao & Whatley, 1992). Later, specimens were discovered, but not identified, in Lake Nakaumi, Shimane Prefecture, SW Japan (Fig. 1) (as Cytheridae gen. et. sp. indet. by Tanaka et al. (1998) and Sanyuania sp. by Seto et al. (1999)). Further examination of these Japanese specimens has clarified that they are conspecific with the Chinese specimens. This has provided an opportunity to review the distribution (Fig. 1) and potential environmental significance of Sanyuania cuneata and, for the first time, to describe its appendages (Fig. 2).

Specimens figured herein were recovered from Lake Nakaumi (35°26′ 50″ N, 133°07′50″ E) at a depth of 0.3–6.0 m and salinity of 8–17 psu on 9 September 1998. The surface of the sediment was covered by the byssus of the mussel Musculista senhousia (Benson, 1842).

Sanyuania cuneata is probably endemic to the East China Sea and the southwestern part of the Sea of Japan and is a potentially useful palaeoenvironmental indicator of brackish (steno-haline) environments in the area. By using the oxygen isotopic data from planktonic foraminifers and the estimated value of salinity flowing into the Japan Sea, Matsui et al. (1998) approximated that the salinity of the surface water of Japan Sea declined to about 20 psu during the Last Glacial Maximum . . .