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a family of the class of bivalve mollusks (Bival-via). The Trigoniidae appeared in the Triassic and are now represented by a single relict genus that dwells off Australia. The shell consists of two identical thick-walled valves, usually with a distinct sculpture of furrows and tubercles. The anterior and posterior portions of the valve are separated by a keel and are sculpturally distinct. The Trigoniidae lived in seas and maintained a crawling mode of life. They are important for the stratigraphy of the Jurassic and Cretaceous, when they were widespread throughout the world.