Here's why:
* Lack of defined cell layers: Tissues are groups of similar cells that work together to perform a specific function. True tissues are organized into layers, like the ectoderm, mesoderm, and endoderm found in more complex animals. Sponges lack these distinct layers.
* Loosely organized cells: Sponge cells are scattered throughout the body and are held together by a gelatinous matrix. They don't form the tight, organized structures found in tissues.
* Limited cell specialization: While sponge cells have some specialization (like collar cells for filtering water), they don't exhibit the same level of complex organization and differentiation seen in tissues of more complex animals.
Therefore, although sponges are multicellular, they are considered to be parazoa (meaning "beside animals"), indicating their simpler organization compared to other animals with true tissues.
