<p>Tectarius muricatus (Linnaeus, 1758) - beaded periwinkle snails on phytokarst.
</p><p>These snails are on a phytokarst surface of aragonitic calcarenite limestones of the Hanna Bay Member (upper Rice Bay Formation, middle to upper Holocene).  They are supratidal rocky shore bacteria/algae grazers.  The jagged, pitted rock surface is phytokarst, formed by limestone being subjected to slow, partial dissolution by the life activities of bacteria and algae that coat the surfaces (= dark gray films).  The snails are feeding on these biofilms by using their radulas to scrape away at the substrate.  Phytokarst is one type of epikarst - limestone dissolution features at the top of the vadose zone.
</p><p>Classification: Animalia, Mollusca, Gastropoda, Littorinidae
</p>
Locality: rocky cliffs along southern shoreline of Graham’s Harbour, just west of Bahamas Field Station, northern margin of San Salvador Island, eastern Bahamas
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a>
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jsjgeology/15382863483/">Tectarius muricatus (beaded periwinkle snails) on phytokarst (San Salvador Island, Bahamas) 4</a>