INVERTEBRATES

• Invertebrates are animals without a backbone or bony skeleton.

• They range in size from microscopic mites and almost invisible flies to giant squid with soccer-ball-size eyes.

• Invertebrates are by far the largest group in the animal kingdom: 97 percent of all animals are invertebrates. 1.25 million species have been described, most of which are insects, and there are millions more to be discovered.

​Molluscs are animals with soft bodies.

They have a muscular feet which they use to move around. Some molluscs have shells. Slugs, snails and octopuses are molluscs.

​Annelids are worms with bodies

divided up into rings (segments).

They do not have legs but they do

have tiny bristles called chaetae.

Earthworms are annelids.

​Arthropods are invertebrates with jointed legs. Their bodies are divided into segments. Arthropods have a skeleton on the outside of their bodies, called an exoskeleton.

Arthropods are the most common kinds of animals on Earth. There are several different groups of arthropods.

​Insects are arthropods with six jointed legs. Their bodies are divided into three parts-a head, thorax and abdomen. Each of these parts is made up of several segments. Most insects have two pairs of wings attached to their thorax. The legs are also attached to the thorax. They have one pair of antennae on their head.

​Arachnids are arthropods with eight

jointed legs. They do not have wings or antennae. Spiders and scorpions are arthropods.

​Crustaceans are arthropods with tough exoskeletons. They have more than four pairs

of jointed legs. They have two pairs of antennae.

Lobsters, water fleas, and woodlice are crustaceans.

​Myriapods are arthropods with many pairs of jointed legs. They have one pair of antennae. Millipedes and centipedes are myriapods.

• ​Invertebrates are animals without backbones.

• Some important invertebrate groups are the molluscs, annelids and arthropods.

• Arthropods are divided into four main groups: insects, arachnids, crustaceans and myriapods.