Pterotracheoidea - Information and photographs from the Tree of Life web project on the Heteropods, a group of pelagic snails found mostly in the tropics and subtropics. Caenogastropoda - Information from Wikipedia on this large taxonomic group of mostly marine snails and their classification. Crepidula aculeata: Spiny Slippersnail - Photographs and information on this species, including its taxonomy, description, habitat, distribution, life history, population biology and community ecology. Cerithidea scalariformis: Ladder Hornsnail - Photographs and information on this species, including its taxonomy, description, habitat, distribution, life history, population biology, physical tolerances and community ecology. Crepidula atrasolea: Eastern White Slipper Shell - Photographs and information on this species, including its taxonomy, description, habitat, distribution, life history, population biology, physical tolerances and community ecology. Crepidula depressa: Depressed Slippersnail - Photographs and information on this species, including its taxonomy, description, habitat, distribution, life history, population biology and community ecology. Crepidula ustulatulina - Photographs and information on this species, including its taxonomy, description, habitat, distribution, life history, population biology and community ecology.