Small (L to 10 mm), subcircular, longer than high, posteriorly slightly truncate, moderately inflated. Shell white, slightly translucent and waxy in appearance. Sculpture of many, fine, low, commarginal lamellae and low radial ribs which are broader and more prominent towards the anterior and posterior. Radial ribs are conspicuously fluted where commarginal lamellae cross giving a crinkled appearance. Lunule elongate, lanceolate and impressed, slightly asymmetrical. Ligament internal, short, situated on a broadly triangular resilifer. Hinge: right valve with single, cardinal tooth, anterior and posterior lateral teeth small, posterior tooth elongate. Left valve with two narrow cardinal teeth, a small anterior lateral socket and posterior lateral narrow socket. Anterior adductor muscle scar medium-long, detached for ca. 50 % of length. Posterior scar ovate. Pallial line entire, sometimes partially discontinuous or irregularly lobate. Shell margin crenulate, with crenulations coarser towards anterior and posterior.

Type locality. Intertidal, south coast of Hainan, China.
Distribution. Singapore: Pulau Semakau (NHMUK), Seringat Bay (NHMUK). Malaysia: Langkawi (AMS). Western Thailand: Ao Bang Ben, Kapoe (NHMUK), Ban Bang Ben (NHMUK), Tung Nam Dan, Phang Nga Province (NHMUK), Eastern Thailand: Kungkraben Bay (NHMUK). Cambodia: 5 km E of port, Sihanoukville (NHMUK). Vietnam: Dam Bay near Nha Trang (Zvonareva et al. 2019). China: Hainan (MNHN), Hong Kong (NHMUK), Daya Bay (NHMUK).
Although we formerly recorded Rugalucina vietnamica with a broad lon¬gitudinal range from the northern Red Sea to southern China (Glover and Taylor 2001) we now regard it as having a narrower range along the continental margin of south eastern Asia with few records from islands. Despite intensive sampling by the MNHN Paris Expeditions around Panglao, Philippines (2004, 2005) and Papua New Guinea (2012, 2014) no R. vietnamica were recorded (Glover and Taylor 2016 and unpublished data).

Habitat. Intertidal to shallow subtidal seagrass and muddy habitats. Recorded at high densities in muddy seagrass and mangrove fringe habitats of eastern and western Thailand (Meyer et al. 2008; Rattanachot and Prathep 2016).