Opisthostoma secretum Maassen, 2002
“An endemic species from Sumatra. Conchologically most similar is Opisthostoma coronatum Van Benthem-Jutting, 1952 from peninsular Malaysia. O. secretum differs by the distinctly narrower umbilicus and more oblique top whorls.” (Maassen, 2002)
Maassen (2002) original descriptions on Opisthostoma secretum – “Shell sinistroid, white, slightly translucent. Whorls approximately 3½ (tuba not included); apical whorls distinctly oblique, moderately to distinctly elevated. The penultimate whorl widest, convex or somewhat angular, with the suture well impressed. Constriction hardly distinct, gradual. Tuba consisting of approximately ¾ whorl, touching the body whorls over its entire length, approximately circular in section. Shell with smooth top whorls, the following ones with rather wide, thin and sharp, distinct radial ribs, which are widely spaced on the penultimate whorl (5 ribs/0.5 mm). Ribs crossed by fine spiral striation. Umbilicus open, deep, very narrow. Aperture tilted 15-45° with regard to the coiling axis, its upper margin clearly below the level of the apex. Without apertural teeth. Peristome double. Outer peristome spreading beyond the inner one, but gradually narrowed towards the right side of the aperture, where it is absent; inner peristome somewhat spreading, distinctly protruding beyond the outer one and one the right side of the aperture attached to one or two whorls of the shell body.”
Opisthostoma secretum – “Dimension: H 0.7-0.8 mm; B 1.2-1.3 mm (including tuba), B 0.8 mm without tuba.” (Maassen, 2002)
Type locality – “Kampung Desa Gadut, limestone rocks near the village, E. of Payakumbuh, (00°15’36.0”S, 100°43’58.7”E)” (Maassen, 2002)