Animal Kingdom: Invertebrate and Vertebrate Classification and Body Plans
Domain 3: Animal Kingdom - what is tested
Questions test the criteria used to classify animals: levels of organisation, symmetry, germ layers, coelom, segmentation, notochord and larval features. You must recognise phyla and representative examples, and place vertebrates in classes.
Core rules
- Cellular level: Porifera. Tissue level: Cnidaria. Organ level: Platyhelminthes onwards. Organ-system level: most higher phyla.
- Symmetry: asymmetrical (sponges), radial (cnidarians, adult echinoderms), bilateral (most animals).
- Germ layers: diploblastic (Cnidaria) versus triploblastic (Platyhelminthes onwards).
- Coelom: acoelomate (Platyhelminthes), pseudocoelomate (Nematoda), coelomate (Annelida onwards). Coelom is a true body cavity lined by mesoderm.
- Chordate features: notochord, dorsal hollow nerve cord, pharyngeal gill slits, post-anal tail. Vertebrata is a subphylum; not all chordates are vertebrates.
- Vertebrate classes: cyclostomes, cartilaginous fishes, bony fishes, amphibians, reptiles, birds, mammals. Distinguish by skin, heart chambers, fertilisation and thermoregulation.
Worked example
Classify Rana tigrina. Kingdom Animalia; Phylum Chordata; Subphylum Vertebrata; Class Amphibia; Order Anura; Family Ranidae; Genus Rana; species tigrina. Reasoning: it has a notochord at some stage, a dorsal nerve cord and gill slits in the embryo, so it is a chordate; as an adult it has lungs and limbs, moist glandular skin and external fertilisation, so it is an amphibian.
Traps
Calling sponges coelomates; saying radial symmetry is typical of all echinoderms at all stages; mixing pseudocoelom with true coelom; treating vertebrates as a phylum; confusing oviparous and viviparous mammals; forgetting that amphibians need water for breeding.