nuculanoids

Nuculanoids are a superfamily of bivalve mollusks, belonging to the order Solemyida. They are characterized by their elongated, equivalve shells, meaning both shells are of equal size and shape. The shells are often thin and fragile, and can be covered in a periostracum, a dark, fibrous outer layer. Nuculanoids are infaunal, meaning they live burrowed in soft sediments like sand and mud. They are deposit feeders, using specialized ctenidia (gills) to create a current that draws food particles, such as organic detritus and microorganisms, towards their mouths.

This group is known for its ancient lineage, with fossil records dating back to the Devonian period. Nuculanoids are distributed globally, inhabiting marine environments from shallow coastal waters to the deep sea. They are typically found in areas with low oxygen levels, where their unique physiological adaptations allow them to thrive. Unlike many other bivalves, nuculanoids possess a chemosymbiotic relationship with bacteria. These bacteria live within the gills of the nuculanoid and are capable of metabolizing sulfur compounds, providing the host mollusk with a supplementary source of nutrition. This adaptation is particularly important in the oxygen-poor environments they often inhabit. The superfamily Nuculanoidea contains several extant families, including Nuculanidae and Malletiidae.