Opisthostoma platycephalum van Benthem Jutting 1952

Opisthostoma platycephalum van Benthem Jutting, 1952 Fig. 7 d Opisthostoma (Opisthostoma) platycephalum van Benthem Jutting, 1952: 26, fig. 11. Opisthostoma platycephalum — Maassen 2001: 35; 2002 b: 178, figs 43, 44. Aulia et al. 2024: 43 –50, fig. 2. Plectostoma platycephalum — Marwoto 2016: 18. Material examined. Indonesia • South Sumatra, Ogan Komering Ulu, Semidang Aji, Padang Bindu (Plot 2); 4°04.00'S, 103°55.79'E; alt. 158 m; May-June 2021; A. S. Nurinsiyah leg.; MZB Gst. 23866/26 • South Sumatra, Ogan Komering Ulu, Semidang Aji, Suka Merindu (Plot 7); 4°04.06'S, 103°55.52'E; alt. 126 m; May-June 2021; A. S. Nurinsiyah leg.; MZB Gst. 23867/39 • South Sumatra, Ogan Komering Ulu, Semidang Aji, Suka Merindu (Plot 11); 4°04.11'S, 103°55.34'E; alt. 124 m; May-June 2021; A. S. Nurinsiyah leg.; MZB Gst. 23868/25 • South Sumatra, Ogan Komering Ulu, Semidang Aji, Suka Merindu (Plot 8); 4°04.06'S, 103°55.40'E; alt. 134 m; May-June 2021; A. S. Nurinsiyah leg.; MZB Gst. 23869/2 • South Sumatra, Ogan Komering Ulu, Semidang Aji, Padang Bindu (Plot 13); 4°04.24'S, 103°55.70'E; alt. 170 m; May-June 2021; A. S. Nurinsiyah leg.; MZB Gst. 23870/3 • South Sumatra, Ogan Komering Ulu, Semidang Aji, Suka Merindu (Plot 5); 4°04.04'S, 103°55.36'E; alt. 150 m; May-June 2021; A. S. Nurinsiyah leg.; MZB Gst. 23871/16. Description (n = 45). Shell minute size with H = 1.2–1.9 mm (mean 1.6 mm); D = 1.7–2.6 mm (mean 2.3 mm); Diameter without aperture = 1.2–1.8 mm (mean 1.5 mm); HA = 0.7–1.1 mm (mean 0.9 mm); DA = 0.7–1 mm (mean 0.8 mm); 3.5 whorls. Shell dextral; apical spire whorl with a depressed conical shape; top whorls in one plane, somewhat oblique on the axis of the shell; whitish color; protoconch smooth; second whorl with smooth rather close ribs (9–20 ribs per mm or total 18–26 ribs) slightly obliquely; following whorl (body whorl) has more distant ribs (4–8 ribs per mm or total 12–18 ribs); last whorl trumpet-shaped, towards the aperture, directed upward, but not deviating transversely, separated by a deep suture; shell height mm, shell width mm (without aperture) or (with aperture). Round aperture, aperture width mm, aperture height mm. Peristome continuous, double; umbilicus open, deep, very narrow. Habitat. Limestone rocks. Distribution. The species was previously recorded in Peninsular Malaysia, Aceh, and North Sumatra (Maassen 2002 b). The distribution in South Sumatra is a new record (Aulia et al. 2024). Remarks. All specimens of O. platycephalum from Padang Bindu Karst, South Sumatra are larger than those described by van Benthem Jutting (1952). Holotype: shell height 0.6 mm, shell diameter 1.2 mm, aperture diameter 0.4 mm; paratype with shell height 0.6–0.7 mm, shell diameter 1.1–1.2 mm, and aperture diameter 0.4 mm. According to van Benthem Jutting (1952), O. platycephalum has a shell that is not transparent, whereas a few O. platycephalum specimens from the Padang Bindu Karst are slightly transparent. Specimens from the recent collections probably fresher compared to the specimen examined by van Benthem Jutting because old shells tend to become opaque due to weathering. Based on the overall characteristics of shell morphology, the Opisthostoma samples found in Padang Bindu were identified as O. platycephalum. We follow the updated classification in MolluscaBase (2025) to include the species to the genus Opisthostoma.