Zhang, Jun-Long, Xu, Feng-Shan & Liu, Rui-Yu, 2012, The Myidae (Mollusca, Bivalvia) from Chinese waters with description of a new species, Zootaxa 3383, pp. 39-60: 53

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http://doi.org/ 10.5281/zenodo.281734

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Tugonia  ( Distugonia  ) sp.

Figure 7 A –LView FIGURE 7. A – L

Distugonia  sp. Xu, 2008: 590.

Material examined. MBM 188705 (1 articulate shell), MBM 188706 (1 right valve), shells collected from dead coral, intertidal zone, Sanya, Hainan Island, China by Ma Xiu-tong, on March 28 th, 1958.

Description. Length to 9 mm; shell equivalve, inequilateral, elongate, thin, chalky, the anterior part of the shell more inflated than the posterior part, gaping posteriorly; posterior area small, truncated, anteriorly demarcated by weak ridge; umbo almost central, low and prosogyrate; anterodorsal margin convex, anterior margin broadly rounded; posterodorsal margin rather straight; posteroventral margin weakly curved to almost straight.

Sculpture fine, with irregular commarginal growth lines and swellings, becoming weak or disappearing in middle part, devoid of any radial rib, posterior area with strong commarginal lamellar sculpture; colour greyish with periostracum yellowish; inner shell surface with chalky blotches.

Spoon-shaped chondrophore in left valve extending posteriorly; chondrophore in right valve horizontally compressed.

Anterior muscle adductor scar thin and elongate; posterior adductor scar ovate; pallial sinus shallow, wide and barely visible; pallial line obscure.

Remarks. We think this species is new and are working to resolve this question. Tugonia  ( Distugonia  ) sp. differs from T. (D.) decurtata ( Adams, 1851)  ( Figs. 6View FIGURE 6. A – K L, 7 M) by its smaller posterior area which is demarcated by a less pronounced ridge, larger and rather flat umbo, and a more strongly curved dorsal margin. Our species also differs from T. (D.) inopinata ( Iredale, 1936)  ( Fig. 7View FIGURE 7. A – L N, O; see also Lamprell & Stanisic, 1998: 7, fig. 4 a –d) by its more regular shell; the rather concave posterodorsal margin of T. (D.) inopinata  makes the shell more irregular; and the umbo is rather prominent.