👉 Opistobranchia are a group of marine invertebrates that primarily inhabit freshwater habitats, often living in saltwater systems like estuaries and rivers. They include brachiopods (brachycladons), bivalves (scallops and clams), and gastropod mollusks. Opistobranchs are known for their unique ability to form complex structures called opists, which can vary in shape from a simple tube or hollow shell to
