The calcareous shells have a cover (operculum) and two curved supports known as helens. Most are one to four centimeters in length and are triangular or elliptical in cross section. Some species have rings or stripes.
| Graph IRI | Count |
|---|---|
| http://dbkwik.webdatacommons.org | 18 |
![[RDF Data]](/fct/images/sw-rdf-blue.png)
