Chapter 4 — Animal Kingdom

Animal Kingdom classification organizes over one million animal species based on fundamental features like body organization level, symmetry, coelom presence, and segmentation, with 11 major phyla ranging from simple sponges to complex chordates with notochords.

Animal Kingdom is classified into 11 major phyla based on shared fundamental features including levels of cellular organization (cellular, tissue, organ, organ-system), body symmetry (radial or bilateral), presence or absence of coelom, segmentation, and notochord presence. These classification criteria help assign systematic positions to newly described species. The phyla span from primitive Porifera (sponges) with cellular-level organization to complex Chordata featuring notochord, dorsal hollow nerve cord, and pharyngeal gill slits. Key distinctions include whether digestive and circulatory systems are complete or incomplete, and whether animals are diploblastic or triploblastic.

1. 01Porifera (sponges) are multicellular with cellular-level organization and water canal systems for food gathering and waste removal.
2. 02Coelenterata (cnidarians) exhibit tissue-level organization, are diploblastic with radial symmetry, and possess cnidoblasts (stinging capsules) for prey capture.
3. 03Platyhelminthes (flatworms) are bilaterally symmetrical, triploblastic, acoelomate animals with incomplete digestive systems.
4. 04Annelida (segmented worms) and Arthropoda (insects and relatives) show metameric segmentation and are coelomate animals with complete digestive systems.
5. 05Chordata possess notochord, dorsal hollow nerve cord, and pharyngeal gill slits; vertebrates replace the notochord with a vertebral column in adults.
6. 06Vertebrata subdivides into seven classes: Cyclostomata (jawless), Chondrichthyes (cartilaginous fishes), Osteichthyes (bony fishes), Amphibia, Reptilia, Aves, and Mammalia.