Final answer:
The perineum is NOT a serous membrane, unlike the peritoneum, pleura, and pericardium which are serous membranes that reduce friction in the body's coelomic cavities. The correct option is D.
Step-by-step explanation:
The structure that is NOT a serous membrane is d. perineum. Serous membranes are epithelial membranes composed of mesodermally derived epithelium, known as the mesothelium, and are supported by connective tissue.
These include the peritoneum, which lines the peritoneal cavity surrounding several abdominopelvic organs; the pleura, which surrounds the lungs in the pleural cavity; and the pericardium, which surrounds the heart in the pericardial cavity.
The serous membranes are essential as they form fluid-filled sacs that reduce friction between organs and the body wall, thus cushioning and protecting the organs within these cavities. On the other hand, the perineum is not a serous membrane but an area of the body between the pubic symphysis and the coccyx, including the perineal body and surrounding structures.