Final answer:
The incorrect statement about serous membranes is that 'They are continuous with the external environment.' Serous membranes line body cavities that do not open to the exterior and are part of the pleura, pericardium, and peritoneum, which all secrete fluid to reduce friction between organs and the body cavity wall.
Step-by-step explanation:
The statement that is NOT a characteristic of the serous membrane is: 'They are continuous with the external environment.' Serous membranes are actually lined body cavities closed to the exterior of the body. They include the pleura (associated with the lungs), the pericardium (associated with the heart), and the peritoneum (associated with the abdominal and pelvic organs). These membranes secrete serous fluid to reduce friction and are a paired membrane whereby one layer adheres to an organ (visceral layer), and the other lines a cavity wall (parietal layer).