Land Snails of Dåno′ (Cocos Island), Mariana Islands

We performed the first survey of terrestrial gastropods on Dåno′ (Cocos Island). Dåno′ is a 0.33 km2 uninhabited atoll island located 2.5 km southwest of Guam, the largest island in the Mariana archipelago, western Micronesia. In 4 days of examining vegetation, soil, and leaf litter, we found 14 species of mollusks arrayed in 12 genera and 11 taxonomic families. The fauna is a subset of that found on Guam. Five species are native to the Mariana Islands, two of which are endemic to the archipelago, and the remaining seven are likely introduced there, perhaps prehistorically. Ground-inhabiting species found only as abundant worn shells in soil suggest relatively recent turnover of these forms, perhaps from seawater inundation of the low-lying island during typhoons. There was no evidence of Mariana endemic snails in the family Partulidae, recently afforded legal protection under the U.S. Endangered Species Act. However, neither did we encounter the invasive flatworm Platydemus manokwari De Beauchamp, currently decimating partulids elsewhere in the Marianas. Hence, we suggest that if further surveys confirm the predator’s absence, Dåno′ might serve as a novel sanctuary for transplanted populations of Guam’s most endangered snails.