Steven+Mason

Final Project

Steven Mason Hr.6 multicellular animals (called metazoans) are usually included in general biology courses. Remember that the botanical counterpart of a phylum is called a division. Unicellular animals (called protozoans) are usually placed in the kingdom Protista along with the divisions of unicellular and multicellular algae. True multicellular animals are typically without cellulose cell walls and photosynthetic pigments, and they form diploid embryos developing from a blastula stage. The blastula is a hollow, fluid-filled sphere bounded by a single layer of cells surrounding a central cavity or blastocoel. Multicellular animals are heterotrophic by ingestion of food into a body cavity (coelom) that is completely lined by the mesoderm. Primitive phyla without a true coelom include the Porifera and Coelenterata (Cnidaria). Animal phyla are classified according to certain criteria, including the type of coelom, symmetry, body plan, and presence of segmentation.