What organs do snails, such as periwinkles, use to breathe?
Periwinkles, and the other animals that people refer to as “snails”, are classified by zoologists as members of the Class Gastropoda in the Phylum Mollusca (they are often referred to as “gastropod molluscs”). Gastropods, like the other molluscs, evolved in the ocean so most use gills to extract oxygen from the water. (The actual structure of the gills can vary a lot among the different gastropods.) For protection, the gills are often (but not always) contained inside a chamber (or space) inside the animal’s shell and over its head called the mantle cavity. The location of the mantle cavity and the gills is marked on the diagram. Some gastropodsthe land snails and slugs are well known examplesmoved onto land and, in the process, lost their gills. Instead of gills, these animals extract oxygen from the air using the lining of their mantle cavity. This tissue became heavily supplied with blood vessels to aid this process. (This is also shown on the diagram.) Just to confuse the issue, so
