Almost terrestrial: Small supratidal species of Nerita (Gastropoda, Neritidae) in the Western Pacific

Several small-bodied, taxonomically confusing species of Nerita (Cymostyla) occupy the highest reaches of the marine intertidal zone on Indo-West Pacific shores. We provide molecular and morphological evidence that N. filosa Reeve, 1855, N. guamensis Quoy and Gaimard, 1834, N. helicinoides Reeve, 1855, and N. tristis Pilsbry, 1901, are distinct species. The first three of these species are confined to the highest levels of pitted limestone shores and have narrow geographic ranges. Nerita tristis belongs to a different subclade relative to the other species and has a wider geographic range, occurring on both limestone and volcanic shores. The pitted limestone environment has enabled these small nerites and members of the Littorinidae to become nearly terrestrial.