👉 Elasmobranchia, also known as brachyhermians or brachiopods, are a group of bivalve mollusks that share a common ancestor with crustaceans. They have a single nucleus and a single cell wall, and their shells are composed of multiple layers of cells arranged in a series of interlocking rings called the shell margin. Elasmobranchia were once thought to be primitive invertebrates but now are recognized as part of the
