Final answer:
The operculum in bryozoans is regulated by muscular action and nerve signals, similar to other aquatic invertebrates. These muscles are part of an individual zooid's anatomy, which allows them to close off their exoskeletal opening for protection and environmental interaction.
Step-by-step explanation:
The operculum in bryozoans, a type of aquatic invertebrate, is controlled by their muscles. Bryozoans, often referred to as "moss animals," are filter feeders that form colonies. Each individual, known as a zooid, is equipped with an operculum, which functions as a door or lid to close off the opening of their exoskeleton when retracted.
While the question does not detail the specific biological mechanisms, it is generally understood that the movement of the operculum in bryozoans, similar to other muscle-controlled processes in aquatic invertebrates, would be regulated by a combination of muscular action and nerve signals, facilitated by the organism's nervous system.
In contrast to bryozoans, scyphozoans (such as jellyfish) have a nerve net and muscle rings for contraction. However, these are part of their locomotion and feeding mechanisms, not controlling an operculum, which they do not possess. Bryozoans differ in their hard calcium carbonate skeletons and the presence of the operculum, which they use for protection and to control their interaction with the environment.