(Shell of Opisthostoma vermiculum) Photo courtesy of Reuben Clements
Name: Opisthostoma vermiculum
Common Name: None
How it made the Top 10: This species represents a unique morphological evolution in its manner of shell twisting. Most gastropod shells tightly coil according to a logarithmic spiral and have an upper limit of three coiling axes. The shell of O. vermiculum, however, possesses four different coiling axes - the most for any known gastropod. In addition, the whorls detach three times and reattach twice to preceding whorls in a fairly consistent manner, which suggests that the coiling strategy is under some form of strict developmental-gene control. Opisthostoma vermiculum appears to be restricted to a single limestone karst.
Reference: Clements, R., T.-S. Liew, J.J. Vermeulen and M. Schilthuizen. 2008. Further twists in gastropod shell evolution. Biology Letters 4: 179-182.
Type material: "Holotype: ZRC.MOL.002824, Gunung Rapat (4° 33' N, 101° 7' E), Perak, Peninsular Malaysia, held in RMBR. Two paratypes: ZRC.MOL.002825 and ZRC.MOL.002826, same data as holotype."
Type locality: Gunung Rapat, Perak, Malaysia.
Etymology: The specific epithet, vermiculum, is derived from Latin, "meaning wormy."