Songkhlanaia tamodienica Konopleva, Lheknim, Sriwoon, Kondakov, Vikhrev & Bolotov, 2023, 2022

Songkhlanaia tamodienica Konopleva, Lheknim, Sriwoon, Kondakov, Vikhrev & Bolotov, 2023

Figs 2 A, B View Figure 2 , 5 A View Figure 5 , Table 1 View Table 1

Songkhlanaia tamodienica Konopleva et al., 2023: 14, fig. 2 c – h. Type Locality: “ Southern Thailand: Klong Plug Pom, middle reach of Klong Tamod, Songkhla Lake Basin, Ban Kok Sai, Tambon Mae Kree, Tamod District, Phatthalung Province, 7.3324 ° N, 100.0917 ° E ”. Bolotov et al. 2023: 12. View in CoL

Material examined.

Thailand – Phatthalung Province • 7 shells; Tamot District, Mae Khari Subdistrict, Songkhla Lake Basin, Tamot Stream ; 7.3302 ° N, 100.0873 ° E; 17 May 2023; E. Jeratthitikul leg.; MUMNH - UNI 2956 View Materials to 2960 View Materials , UNI 2971 View Materials to 2972 View Materials GoogleMaps .

Diagnosis.

Shell medium, rectangular, thin, rather compressed. Anteriorly constricted, dorsal margin straight, slightly elevated posteriorly. Posterior slope with two prominent folds. Umbo tiny, slightly elevated. Shell surface with fine irregular growth lines, roughened on posterior slope. Right valve with one smooth tubercular or triangular pseudocardinal tooth, left valve with somewhat lingula-shaped tooth. V-shaped furrow on posterior end of hinge structure weak, not prominent. Anterior adductor muscle scar shallow, somewhat drop-like, contiguous with anterior protractor muscle scar. Umbo cavity shallow.

Differential diagnosis.

This species can be distinguished from the other two congeners by its much smaller (about half size) and thin shell, rectangular shape, and rather compressed lateral profile. It can also be distinguished by 39 fixed nucleotide substitutions in the COI gene fragment (Table 3 View Table 3 ).

Distribution.

So far, known only from the type locality in Songkhla Lake Basin, southern Thailand (Fig. 3 View Figure 3 ).

Comments.

Songkhlanaia tamodienica was described based on a single specimen. The holotype has a relatively small (shell length 44.2 mm), thin, lighter colored shell with shallow adductor muscle scar, and slightly elevated posterior wing ( Konopleva et al. 2023: fig. 2 c – h). This specimen appeared to be small and young individual. Recently, we revisited the type locality and collected seven more specimens; two of these shells are larger in size and probably from fully grown specimens. They exhibit a thickened and inflated shell, rounded posterior end, dark periostracum, deep adductor muscle scar, and less pronounced posterior wing (Fig. 2 A View Figure 2 ). The largest specimen measured is 67.3 mm in shell length. In addition, the outer shell surface is sculpted by irregular growth lines, which are pronounced on the posterior slope and border of the shell (Fig. 2 A View Figure 2 ). This feature is present in younger specimens but is less prominent (Fig. 2 B View Figure 2 ).