to be added
Critically Endangered B2ab(ii,iii)
Holotype: ZMA 136049(1) (Seen). Paratypes: ZMA 136050(>10) (Seen).
See under Plectostoma turriforme.
Type locality. Bukit Panching, Pahang (3°53'28"N, 103°8'26"E).
Distribution range. Endemic to Bukit Panching (not seen in Figure 18A because its symbol overlaps with Plectostoma senex).
Apex. Shape: distinctly convex.
Spire. Height: 2.6–2.9 mm. Width: 1.5–1.6 mm. Number of whorls: 4 1/4–5 1/2. Apical spire shape: oblong conical. Basal spire shape: ovoid. Whorl periphery: distinctly convex. Umbilicus: completely closed by tuba.
Constriction. Parietal teeth: two. Basal teeth: none.
Tuba. Coiling direction: type 3 and aperture visible in left lateral view. Tuba whorl length in proportion to spire last whorl: ca. 3/8. Proportion of tuba that attaches to spire: whole.
Aperture and peristome. Peristome: double peristomes. Outer peristome shape: same as inner peristome and uniformly projected all around, except the posterior part.
Spiral lines. Thick lines: present. Thin lines: present.
Radial ribs. Rib density: 6–8 ribs per mm. Rib intensity: thin. Shape: slightly curved.
Extinct. Its only habitat–Bukit Panching, has been completed quarried away (see alsoSchilthuizen and Clements 2008). The ruin is now inundated. The status of this species in a previous assessment (IUCN redlist) was: Critically Endangered B2ab(ii, iii) ver. 3.1 (Clements 2009a).
Shares with Plectostoma senex and Plectostoma turriforme the tuba form, but differs by lacking basal constriction teeth.
“The new species is very similar to the preceding one. It possesses, however, fewer whorls and is not quite so slender as O. (P.) turriforme.” (Benthem-Jutting, 1952)
Benthem-Jutting (1952) original descriptions on Opisthostoma (Plectostoma) sciaphilum – “Shell high-turreted, yellowish, fawn or pinkish-brown. First 1 ½ whorl smooth, subsequent ones ornamented with elegant, oblique white ribs, distantly placed and standing out wing-like away from the shell. This is especially the case on the periphery of each whorl, rendering their profile falsely angular. Between the ribs there is a delicate spiral sculpture. Not transparent and only little shining. Whorls 7-7 ½, convex, regularly increasing in size. Top whorls not markedly oblique on the rest of the shell. Last whorl about midway somewhat constricted transversely, then widening towards the aperture and irregularly curved, although not so bizarre as in O. (P.) salpidomon and previous species. Suture deep. Umbilicus closed. Aperture round, vertical or a little obliquely facing downward. Adnate to the previous whorl. Peristome continuous, circular, with a wing-like ribs behind the peristome and parallel to it. Operculum unknown.”
Opisthostoma (Plectostoma) sciaphilum – “Dimensions: Height 3.0-3.6, Breadth 1.5-1.6, Diam. apert. 0.9-1.1 mm.” (Benthem-Jutting, 1952)
Type locality – “Malaya: Bukit Panching, near Kuantan, Pahang” (Benthem-Jutting, 1952)
