The Fat Dove Snail
At about 5 mm length (0.2 inch), the Fat Dove Snail, Parvanachis obesa (C.B. Adams, 1845) is one of the smallest local species of the Dove Snail family (Columbellidae). The live animals (on the right) were picked from stranded seaweed collected by Museum Marine Biologist Rebecca Mensch on Sanibel, in January 2015, and photographed by me at the Museum’s photography facility. As seen in the photo, Dove Snails (and other micro-gastropods) are capable of "crawling upside down" under the interface air-water; they do so by taking advantage of the surface tension (caused in turn by the cohesive forces among water molecules). The smaller the critter, the easier it will be for them to crawl along the air-water interface. Same is true for insects, spiders, and other air-breathing critters capable of walking on the water surface.
The Fat Dove Snail, Parvanachis obesa, from Sanibel.