Sinocytheridea impressa (Brady, 1869)

Fig. 5I–O

Cytheridae impressa Brady, 1869: 158, pl. 16 figs 13–14.

Cyprideis yehi Hu & Yeh, 1978: 157–159, pl. 3 figs 10–13.

Sinocytheridea sinensis Hou in Guan et al., 1978: 240, pl. 65 figs 1–5.

Sinocytheridae latiovata Hou & Chen in Hou et al., 1982: 164–165, pl. 72 figs 10–20.

Sinocytheridae longa Hou & Chen in Hou et al., 1982: 165, pl. 72 figs 1–9.

Eucytheridae sinobesani Hu, 1984: 76, pl.10, figs. 27, 28.

Sinocytheridea impressa – Whatley & Zhao 1987: 24, pl. 1 figs 8–10. — Montenegro et al. 2004: pl. 2 figs 6–7. — Alberti et al. 2013: 341. — Yamada et al. 2014: 110. — Hong et al. 2017: 58; 2019: 596. — Cheung et al. 2019: 9. — Tanaka et al. 2019: fig. 7. — Tan et al. 2021: fig. 2(10).

Dimensions

L = 0.515 –0.567 millimeters, H = 0.250 –0.317 millimeters, H/L = 0.45–0.49 (males; Fig. 5J–K, M–N).

L = 0.477 –0.700 millimeters, H = 0.246 –0.410 millimeters, H/L = 0.52–0.59 (females; Fig. 5I, L, O).

Distribution

Tanaka et al. (2019) recently reviewed and presented the distribution of extant and fossil Sinocytheridea impressa around the eastern margin of Eurasia, from the Sea of Japan to South China Sea. The reader is referred to their work for details. Here, we list some occurrences of the species.

Modern distribution: Japan (Tanaka et al. 2019); China (Zhao & Wang 1988, 1990; Cheung et al. 2019); Hong Kong (Brady 1869; Hong et al. 2017, 2019); Central Vietnam (Tan et al. 2021). Mae Khlong estuary, NW Gulf of Thailand, Thailand (Montenegro et al. 2004); Klong Thom, Krabi, Andaman estuary, Thailand (Yamada et al. 2014).

Fossil distribution: Upper Pliocene, Japan (Yamada et al. 2002); Middle Pleistocene, Japan (Ishizaki 1990; Irizuki et al. 2005). Pliocene, China (Hou & Gou 2007); Pliocene to Pleistocene, China (Lee & Paik 1992; Hu & Tao 2008); Quaternary, China (Huang 1985; Hou et al. 1982; Alberti et al. 2013); Pleistocene to Holocene, Hong Kong (Cao, 1998); Bangkok Clay (samples 20SS01A, 01B, 02A, 02B, 03A, 04A, 04B), whale excavation site, Samut Sakhon Province, Thailand, Late Holocene (this work, Fig. 4).

Remarks

Carapaces of Sinocytheridea impressa (Brady, 1869) are characterized by flat, elongate to oval lateral outline, long hinge, slightly concave VB, with scattered sieve type pores on carapace surface. Sexual dimorphism clear: males are longer and slender with AB and PB nearly of equal size, Hmax located anteriorly but not distinct; females are shorter, with AB larger than PB, Hmax located anterior to midL and distinct. The juvenile carapaces are very delicate and transparent.