Théel (1882) originally described seven species in his genus Scotoplanes. In a recent monograph, Danish biologist Bent Hansen (1975) reduced the number of Scotoplanes species to two. More recent research by Russian biologist Andrey Gebruk (1983) indicated at least five species of Scotoplanes. Recent studies of these animals at the Scripps Institution of Oceanography at La Jolla, California, indicate that there may be as many as eight species (Dave Pawson, in litt. December 2009). Molecular analyses may soon help clarify the systematics (i.e., evolutionary relationships and species boundaries) of this group.