Vertebrate and arthropod groupsSpec 1.3.2, 1.3.3
In short
Vertebrates are animals with a backbone, split into five groups: mammals, birds, reptiles, amphibians and fish. Arthropods have a hard exoskeleton, a segmented body and jointed legs, and are split into myriapods, insects, arachnids and crustaceans. Insects have three body parts and three pairs of legs; arachnids have two body parts and four pairs of legs.
The animal kingdom is split into smaller groups. You need the five groups of vertebrates (animals with a backbone) and four groups of arthropods (animals with jointed legs).
Vertebrates
| Group | Main features |
|---|---|
| Mammals | Body covered with hair or fur; young develop in the mother and are fed on milk from mammary glands; external ears (pinnae) |
| Birds | Body covered with feathers; two wings and two scaly legs; a beak; lay eggs with hard shells |
| Reptiles | Dry skin covered with scales; lay eggs with soft, leathery shells; most live on land |
| Amphibians | Moist, smooth skin without scales; lay jelly-covered eggs in water; larvae (tadpoles) live in water; adults often live on land |
| Fish | Body covered with wet scales; fins; gills for gas exchange; lay soft eggs in water |
Arthropods
All arthropods have a hard exoskeleton, a body made of segments, and jointed legs. They are split into four groups by the number of legs and body parts.
| Group | Main features | Example |
|---|---|---|
| Myriapods | Long body made of many similar segments; many pairs of legs, one or two pairs on each segment; one pair of antennae | Centipede |
| Insects | Body in three parts (head, thorax, abdomen); three pairs of legs; one pair of antennae; usually two pairs of wings | Housefly |
| Arachnids | Body in two parts (cephalothorax and abdomen); four pairs of legs; no antennae and no wings | Spider |
| Crustaceans | More than four pairs of legs; two pairs of antennae; breathe using gills; most live in water | Crab |
(opens full size in a new tab)Classifying an organism
To classify an organism, first decide its kingdom using the animal and plant features. Then match its features to the group descriptions. An animal with a backbone, feathers and a beak is a bird. An animal with a hard exoskeleton, eight legs and two body parts is an arachnid.
Do not name a group from one feature alone. Many groups lay eggs, but only birds have feathers and only mammals have fur and mammary glands.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026