“From the conchologically most similar species O. umbilicatum it can be distinguished by the absence of a spiral striation, the more convex whorls, the different attachment of the aperture, and the shorter tuba.” (Maassen, 2001)
Maassen (2001) original descriptions on Opisthostoma (Plectostoma) christae – “Shell dextral, high conical, reddish brown, shing and transparent; with 5.75 distinctly convex whorls, separated by a rather deep suture, and without a spiral striation. The last whorl is wider than the penultimate one. Radial ribs rather thin, increasingly much higher and sharper on the lower whorls; on the penultimate whorl 5-6 ribs/mm, above the aperture with 5-6 ribs/mm. The constriction consists of a transversal thickening all around, and a small and low, longitudinal tubercle at the angular edge, just entering the transversal thickening. The tuba is 0.5 whorl long and hardly turns off inwards. Umbilicus very narrow. Peristome double; the inner peristome only slightly protruding from the outer. In frontal view, the aperture touches the previous whorl at the right of the middle an is hardly turned upwards. Operculum with a distinct spiral ridge on its outer surface.”
Opisthostoma (Plectostoma) christae – “H 2.7-3.1 mm; B 1.7-2.5 mm.” (Maassen, 2001)