What are the thin, double-layered membranes that cover surfaces in the ventral cavity?

The thin, double-layered membranes that cover surfaces in the ventral cavity are known as the serosa. These membranes are essential in providing a protective layer around the organs within the ventral body cavity, such as the thoracic and abdominal regions. The serosa consists of two layers: the visceral layer, which adheres directly to the organs, and the parietal layer, which lines the cavity walls. This structure allows for frictionless movement of organs, which is particularly important in areas like the heart and lungs that are constantly in motion.

In contrast, mesentery refers to a fold of tissue that attaches the intestines to the abdominal wall but is not a membrane that directly covers surfaces in the ventral cavity. Synovial membranes are found within joints and are responsible for producing synovial fluid that lubricates joints, while cutaneous membranes are the skin, serving as a protective outer covering for the entire body, not specific to the ventral cavity. Thus, the defining characteristics of the serosa make it the correct answer in this context.