Mytiloida

Mytiloida is an infraorder of marine bivalve molluscs. This group includes many familiar bivalves such as mussels and pen shells. Mytiloidans are characterized by their elongated, equivalve shells, meaning both shells are of similar size and shape. The shells are typically inequilateral, with the umbones (the oldest part of the shell) located near the anterior end.

A prominent feature of most mytiloidans is their strong posterior foot, which is used for secreting byssus threads. These threads are strong, elastic filaments that anchor the bivalve to a substrate, such as rocks, pilings, or other organisms. This ability to attach firmly allows them to thrive in wave-swept intertidal zones and subtidal environments.

Mytiloidans are filter feeders, drawing water into their mantle cavity and extracting organic matter and plankton with their gills. They play important ecological roles, acting as ecosystem engineers by forming mussel beds that provide habitat and food for numerous other species. They also contribute to water clarity through their filtration activities.

The infraorder Mytiloida is divided into several families, with the Mytilidae being the largest and most well-known. This family includes common edible mussels like Mytilus edulis. Other families include the Pinnidae (pen shells) and the Dreissenidae (zebra mussels), the latter of which are known for their invasive potential in freshwater systems, though their origins are marine.