Opisthostoma vermiculum: "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." (http://species.asu.edu/2009_species06)

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