Rugalucina vietnamica (Zorina, 1978)

Taylor, John D. & Glover, Emily A., 2019, Unloved, paraphyletic or misplaced: new genera and species of small to minute lucinid bivalves and their relationships (Bivalvia, Lucinidae), ZooKeys 899, pp. 109-140 : 109

Rugalucina vietnamica (Zorina, 1978) Figs 3 , 4

Pillucina vietnamica Zorina, 1978:195, figs 3 & 6).

Pillucina vietnamica : Lutaenko 2000: 383, pl. 1, figs 1, 2; pl. 3, fig. 1.

Pillucina vietnamica (part): Glover and Taylor 2001: 273, figs 7a-g.

Pillucina vietnamica : Glover et al. 2016: 553, fig. H, A-M.

Pillucina angela (Melvill, 1899) (part): Huber 2015: 422, figs p. 76.

Type material.

Pillucina vietnamica syntypes (ZISP), 13 shells and 1 valve, L 5.5-8.9 mm.

Type locality.

Intertidal, south coast of Hainan, China.

Description.

Small (L to 10 mm), sub-circular, 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.

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).

Habitat.

Intertidal to shallow sub-tidal 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). Gill structure and symbiotic bacteria are illustrated in Fig. 4N, O .

Remarks.

Although we formerly recorded Rugalucina vietnamica with a broad longitudinal 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).

Figures

Figure 3. Internal drawings of left valves of Rugalucina and Pusillolucina species. Not to scale.

Figure 4. Rugalucina vietnamica (Zorina, 1978). A-C Pillucina vietnamica Zorina, 1978 syntypes (ZISP), exterior of right valve and interior of left and right valves, Hainan, China, L 5.5 - 8.9 mm D internal drawing of C. E, F R. vietnamica Palau Semaku, Singapore (NHMUK 20150057), L 8.5 mm G-L R. vietnamica Kungkraben Bay, eastern Thailand (NHMUK 20191072) G exterior of right valve, L 7.0 mm. H exterior of left valve, L 7.0 mm I, J interior of left and right valves, L 7.7 mm K dorsal view L 5.6 mm L, M detail of hinge of I and J. N Section through gill of Rugalucina vietnamica Kungkraben Bay, Thailand showing filaments with ciliary (cz) and bacteriocyte zones (bz). Critical-point dried preparation O detail showing abundant bacterial symbionts in bacteriocytes. Scale bars: 20 µm (N); 10 µm (O).