Final answer:
The large central opening in the poriferan body is known as the osculum, which allows water carrying trapped food and waste to leave the sponge after passing over the feeding choanocytes.
Step-by-step explanation:
The large central opening in the poriferan body is called the osculum. The osculum is a vital feature in the anatomy of a sponge, serving as the exit through which water that has entered through tiny pores (ostia) and passed over the choanocytes is expelled. The flow of water through the sponge's body is essential for its feeding, excretion, and respiratory processes. Choanocytes, also known as "collar cells," line the feeding chambers inside the sponge. These cells beat their flagella to generate a water current, trap and ingest food particles by phagocytosis and also play a role in sexual reproduction by differentiating into sperm. The structure and function of the poriferan body, including the osculum, choanocytes, and other specialized cells like pinacocytes, reflect the sponge's simple organization and mode of filter feeding.