has part composed primarily of sediment surface marine faunal bed mussel bed envoCmecs A marine faunal bed which is dominated by mussels of the Mytilus or Modiolus genera either 1) resting on the sediment surface, 2) partially embedded in the sediment, 3) attached to conspecifics (by using their byssal threads), or 4) attached to a piece of gravel in slightly gravelly fine sediments. envoMarine CMECS:532 If individual mussels are present in densities sufficient to construct biogenic substrate, please use the mussel reef class. https://cmecscatalog.org/cmecs/classification/unit/532.html This class aligns to the Coastal and Marine Ecological Classification Standard (CMECS). In ENVO, we may adapt the definition for consistency, but the semantics (meaning) of the term should be unaffected. Please consult the CMECS catalogue (https://cmecscatalog.org/) for authoritative and semantically unconstrained definitions. An excerpt of the CMECS description: "Faunal Beds are highly dependent on substrate type. Individual species and entire biotic communities have adapted specialized anatomies and behaviors for survival on hard substrates; other species and communities have specialized and developed adaptations for life on soft substrates. Generalist fauna also occur (e.g., certain holothurians, crustaceans, and sponges) that can succeed on both substrate types. However, substrate type is such a defining aspect of the Faunal Bed class that CMECS Faunal Bed subclasses are assigned as physical-biological associations involving both biota and substrate." Modiolus Mytilidae ecological community