Aissellidae

Aissellidae is a family of extinct marine bivalve mollusks belonging to the order Pectinida. Fossils of aissellids are found in rocks dating from the Triassic period. The family is characterized by its weakly to moderately convex, equivalve shells, meaning both valves are of similar size and shape. The left valve is typically slightly larger than the right. The external surface of the shell is usually ornamented with concentric growth lines and sometimes fine radial ribs. Aissellids possessed a ctenoid hinge, meaning the hinge line was lined with small comb-like teeth.

These bivalves were sessile organisms, likely attaching themselves to the seafloor or other substrates. Their morphology suggests they were filter feeders, drawing water through their shells to extract small organic particles. The geographical distribution of aissellid fossils indicates they inhabited shallow marine environments across various parts of the world during the Triassic. The exact phylogenetic relationships of Aissellidae within Pectinida are still subject to ongoing research, but they are considered an early lineage within the order. The extinction of the Aissellidae family is presumed to have occurred by the end of the Triassic, though their precise fate and reasons for extinction are not definitively established.