The most primitive cellular animal is considered to be the sponge, which belongs to the phylum Porifera. Sponges lack true tissue organization and specialized organs, making them one of the simplest multicellular organisms. They are filter feeders and live attached to surfaces in aquatic environments.
The most primitive cellular animals are known as protozoans. Protozoans are unicellular eukaryotic organisms, meaning they have a membrane-bound nucleus in their cells. They belong to the kingdom Protista and are considered simple animals because they lack specialized tissues and organs. Examples of protozoans include amoebas, paramecia, and flagellates. These organisms are found in diverse environments, including freshwater, marine habitats, and soil.
