1) Clam genus 
Spisula is a genus of medium-sized to large marine bivalve mollusks or clams in the family Mactridae, commonly known as surf clams. Species in the genus Spisula include: File:Spisula subtruncata.jpg|Spisula subtruncata ...
(from the article `bivalve`) The burrowing Spisula illustrates these changes. It, like Nucula, is equivalve and anteriorly and posteriorly symmetrical (isomyarian). The mantle ...