Biology / Unit 8: Classification and Diversity of Life
8.6 Animals
Notes
Animals are multicellular heterotrophs with no cell walls. Most can move at some stage of life.
- Invertebrates have no backbone; they make up about 95% of animal species (sponges, jellyfish, worms, mollusks, arthropods, sea stars).
- Arthropods (insects, spiders, crustaceans) have an exoskeleton and jointed legs; they are the largest animal group.
- Vertebrates have a backbone: fish, amphibians, reptiles, birds and mammals.
- Symmetry: sponges have none; jellyfish have radial symmetry; most animals have bilateral symmetry (left and right halves).
- Ectotherms (most fish, amphibians, reptiles) rely on outside heat; endotherms (birds, mammals) make their own heat.
Practice
A crab has a hard outer skeleton and jointed legs. It belongs to which group?
An exoskeleton and jointed legs define arthropods.
Which animal has bilateral symmetry?
A butterfly's body can be split into matching left and right halves.
A lizard basks on a warm rock in the morning before hunting. This is because lizards are:
Ectotherms get body heat from their surroundings.
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