Fogedia orientalis Kim, Khim, Witkowski and Park, sp. nov. (Figs 2–15)

LM observations (Figs 2–9): Valves are elliptic-lanceolate to lanceolate, with acutely-rounded protracted apices, 11.5–21 μm in length and 5.5–6.5 μm in width. External central raphe endings are punctiform, while external apical raphe endings are slightly bent to the same direction. Axial area is very narrow and linear throughout. Central area is small and square in shape, formed by two shortened striae one on each side. Typical lateral area is absent in the valve. Transapical striae parallel in the middle of the valve then becoming slightly radiate towards apices, 15–18 in 10 μm. Voigt discordance is barely discernible with LM.

SEM observations (Figs 10–15): External valve face is flat with an abrupt transition to the valve mantle. Axial area is straight and symmetrical with very narrow raphe-sternum (Fig. 10). External central raphe endings are slightly expanded (Figs 10–11). The areolae and transapical striae are evenly spaced. Certain areolae near the central area exhibit different shape compared to other areolae, often being circular in shape. The raphe slit runs relatively straight from the central area to the helictoglossa which is relatively simple and small without twist (Figs 13, 15). Areolae are internally occluded by thin hymenes.

Type:— Gyehwa tidal flat (35°46’ N, 126°36’ E; KO-GY), Korea. Type material collected on 6 August 2003 by Dr J. Ryu. Holotype slide deposited in MABIK (MABIK D10042862).

Etymology:—The species name ‘ orientalis ’ is derived from the Latin ‘oriental’ meaning east, because the species is widely distributed in Northeast Asia.

Distribution:—The species was also observed from various tidal flats on the Korean coast (a mudflat at Gyeonggi Bay, a sandflat in Saemangeum, and a mixed flat near Lake Shihwa) and Chinese coast (three sandflats at Qinhuangdao and Yingkou, in a mixed flat at Yingkou, and in a mudflat at Yancheng) of the Yellow Sea. The species was also found in a sandflat at Minamiarao in the Ariake Sea, Japan. Thus F. orientalis is probably widespread along the coast of the Yellow Sea.

Differential diagnosis:—The species is similar to Fogedia densa in its valve outline, small cell size, and the absence of a lateral area. However, the pattern of striae in F. orientalis is parallel in the middle of the valve, while F. densa has a distinctively radiate striae pattern, thus the two species are readily discernable. Stria density is also much sparser in F. orientalis compared to F. densa.