How do animal sponges differ from most other animals?

Sponges (phylum Porifera) are distinct from most other animals due to their simple, primitive body organization. While they are multicellular animals, they differ in the following key ways:

• Lack of Organs and Tissues: Unlike most animals, sponges do not possess definite organs or tissues. Because of this, some zoologists classify them in the subkingdom Parazoa, meaning "beside animals."12
• Digestive System: Most animals have specialized digestive tracts or cavities. In contrast, sponges lack a mouth and a digestive system. Instead, they utilize a unique water-current system of canals and chambers to filter food particles, which are then digested intracellularly within individual cells, similar to protozoans.345
• Coordination: Sponges lack a nervous coordinating center, yet they maintain an efficient water-flow system through the movement of specialized flagellated cells called choanocytes.14

Despite these differences, molecular data confirms that sponges are genuine animals that share a common ancestor with more complex species.1