Figure 3 A–O
Mya arenaria Linnaeus, 1758: 670 — Hanley, 1842 –1856: 19; Dunker, 1882: 176; Oldroyd, 1925: 198, pl. 32, figs. 1 a & 1 b; Lamy, 1927: 157 –168; Nagao & Inoue, 1941: 145 –147, pl. 32 (1), figs. 11, 12 & 14; MacGinitie, 1959: pl. 25, fig. 5; Bernard, 1983: 57; Bernard et al. 1993: 107; Qi, 1996: 268 –269, fig. 327; Darkina & Lutaenko, 1996: 79; Xu, 1997: 229; Petersen, 1999: 326, figs. 6 A & B; Xu & Zhang, 2008: 257, fig. 809; Xu, 2008: 589; Coan et al. 2000: 470, pl. 100; Huber, 2010: 460 (text-fig.).
Mya communis Megerle von Mühlfeld, 1811: 46.
Mya lata Sowerby, 1812 –1815: 185, pl. 81.
Mya acuta Say, 1822: 313.
Mya mercenaria Say, 1822: 313.
Mya subovata Woodward, 1833: 43, pl. 2, fig. 5.
Mya subtruncata Woodward, 1833: 43, pl. 2, fig. 6.
Mya corpulenta Conrad, 1845: 68, pl. 39, fig. 1.
Mya alba Agassiz, 1839: 1.
Mya japonica Jay, 1856: 292, pl. 1, figs. 7 & 10 — Makiyama, 1935: 137 –139, text-fig. j; Habe, 1955: 22 –23, pl. 7, fig. 12; Fujie, 1957: 406 –409, pl. 1, figs. 1–5; MacGinitie, 1959: pl. 19, figs. 6 & 8.
Mya hemphilli Newcomb, 1874: 415.
Mya elongata Locard, 1886: 383, 586.
Mya paternalis Matsumoto, 1930: 98, pl. 39, fig. 2.
Mya oonogai Makiyama, 1935: 137, text-fig. i.
Mya (Arenomya) japonica Jay, 1856 — MacNeil, 1965: 31 –33, pl. 3, figs. 7, 8 & 10, pl. 4, figs. 1–11, pl. 6, fig. 6; Habe, 1977: 278, pl. 58, fig. 3; Scarlato, 1981: 405 –406, figs. 444–449; Okutani, 2000: 1021, pl. 508, fig. 3.
Mya (Arenomya) japonica oonogai Makiyama, 1935 — Habe, 1955: 22 –23, pl. 6, fig. 3.
Mya japonica oonogai Makiyama, 1935 — Fujie, 1957: 403 –406, pl. 2, figs. 1–6.
Mya arenaria japonica Jay, 1856 —Tchang et al. 1955: 61, pl. 18, figs. 2 & 3.
Mya (Arenomya) arenaria Linnaeus, 1758 — MacNeil, 1965: 33–35, pl. 5, figs. 2–12, pl. 6, figs 1–15, 17 & 18; Bernard, 1979: 194–199, figs. 17 & 18.
Mya (Arenomya) arenaria oonogai Makiyama, 1935 — Yoo, 1976: 139, pl. 33, fig. 9; Habe, 1977: 278, pl. 58, fig. 4; Kwon et al., 1993: 385, fig. 96 - 1; Okutani, 2000: 1021, pl. 508, fig. 2; Kwon et al. 2001: 277, fig. 1132.
Material examined. MBM 264720 (1 articulate shell), Moye Island, Weihai, China, on April 22 nd, 1951; MBM 264722 (2 articutate shells, 1 left valve), fish market, Qingdao, China, collected by Ma Xiu-tong, on September 7 th, 1959; MBM 264721 (1 articulate shell), Shandong Penisula, China, exact locality unknown, on April 1951; MBM 264723 (1 articulate shell), in sand, Cangkou, Qingdao, China, on December 10 th, 1950; MBM 300737 (1 articulate shell), fishpond, Rongcheng, Weihai, China, collected by Ma Xiu-tong, on July, 1951; MBM 136114 (3 articulate shells) fish market, Qingdao, China, on November, 1950; MBM 264731 (1 articulate shell), Qingdao, China, collected by Ma Xiu-tong, on September, 1994; MBM 119998 (1 articulate shell), Sea of Japan, Peter the Great Bay, donated by Dr. Lutaenko K. A. (Institute of Marine Biology, Far East Branch of the Russian Academy of Sciences); MBM 119999 (1 articulate shell) Island of Helgoland, Germany, collected by Xiang Jian-hai, on April, 1984.
Distribution and habitat. Miocene to Recent. Circumboreal. Intertidal to about 20m depth, in sandy mud.
Type locality. Europe.
Diagnosis. Length to 150 mm; shell thick, ovate; posterior shell margin weakly acuminate; left valve slightly larger than right valve; umbo slightly anterodorsal; shell covered with yellowish periostracum; sculpture of strong commarginal growth lines and subdued radials; chondrophore of left valve bounded anteriorly by a ridge, resilifer in right valve; pallial sinus deep, reaching beyond shell center; pallial line well defined.
Remarks. The figure of Mya (Arenomya) arenaria in Keen (1969: N 691, fig. E 153,9) may be misleading in that it shows a pointed pallial sinus which barely reaches the center of the shell and with an apparently discontinuous pallial line. However, in the specimens we examined, and of most figures we found in the literature, the pallial sinus is rounded and reaches beyond the center of the shell, and the pallial line is rugged but entire.
Most Japanese scientists accepted Mya japonica Jay, 1856, and M. japonica oonogai Makiyama, 1935 (or M. arenaria oonogai) as separate species (Fujie 1957, 1962; Habe 1955; Makiyama 1935; Okutani 2000). However, Bernard (1979, 1983), Coan et al. (2000), Nagao & Inoue (1941) and Huber (2010) considered Mya japonica and M. arenaria oonogai as synonyms of M. arenaria. Nagao & Inoue (1941) noticed that the differences between the two groups in southern and northern Japan are linked by many intermediate specimens. Fujie (1962) admitted that M. japonica oonogai closely resembles M. arenaria but hesitated to synonymize the Japanese species without examination of the Atlantic species. MacNeil (1965) considered M. oonogai and M. japonica oonogai as junior synonyms under the name of M. japonica. Bernard (1979) found that M. arenaria and M. japonica could not be separated by statistic analysis.
Our material contains two morphotypes which exhibit the differences mentioned by Fujie (1957), MacNeil (1965) and Nagao & Inoue (1941). One type has a longer and thinner posterior end and regular thin commarginal growth lines similar to M. arenaria (Fig. 3 A–F); the other type is nearly equilateral, with rough commarginal wrinkles and a relatively shorter and more round posterior end similar to M. japonica (Fig. 3 G–I). Bernard (1979) mentioned that M. japonica has a “larger, more alate chondrophore” whereas, according to MacNeil (1965), the chondrophore of M. arenaria “tends to be larger” and “slightly more horizontal”. The chondrophores in our material do not coincide with any of the previous descriptions. Even comparing the type figures of M. arenaria (see The Linnean Society of London 2010) and M. japonica (see Jay 1856: pl. 1, figs. 7 & 10; Higo et al. 2001: fig. 95.8), and material from the Sea of Japan (Fig. 3 J–L) and Germany (Fig. 3 M–O), we could not find significant differences. Hence, available evidence suggests ecophenotypic variation which remains to be tested genetically, however.
According to Fujie (1957, 1962) and others, M. arenaria originated in the Pacific in the Miocene, spread into the Atlantic during the Miocene to Pliocene, and was reintroduced into the East Atlantic and East Pacific by anthropogenic activities after its extinction in these areas during the Pleistocene (see also, Bernard 1979; Conde et al. 2010; Gollasch 2006; MacNeil 1965; Strasser 1999).