Final answer:
Sponges do not have a definite shape and do not possess tissues. Instead, they have specialized cells that perform specific functions like tissues.
Step-by-step explanation:
Sponges, also known as poriferans, do not have a definite shape and do not possess tissues. While they lack true tissues, sponges have specialized cells that perform specific functions similar to tissues. For example, the outer layer of the sponge, called the pinacoderm, acts like our epidermis and provides protection. Other functional 'tissues' in sponges include the mesohyl, which acts as an endoskeleton, and choanocytes, which filter food particles.