Phylum Arthropods
Insects Insects are a very successful group of animals. Their success is mostly due to their exoskeleton and tracheae, which are very good at stopping water from evaporating from the insects’ bodies, so they can live in very dry places. They are mainly terrestrial.
Characteristics: l several pairs of jointed legs l exoskeleton.
Characteristics: l arthropods with three pairs of jointed legs l two pairs of wings (one or both may be vestigial) l breathe through tracheae.
Arthropods are animals with jointed legs, but no backbone. They are a very successful group, because they have a waterproof exoskeleton that has allowed them to live on dry land. There are more kinds of arthropod in the world than all the other kinds of animal put together.
Crustaceans These are the crabs, lobsters and woodlice. They breathe through gills, so most of them live in wet places and many are aquatic. Characteristics: l arthropods with more than four pairs of jointed legs l not millipedes or centipedes l breathe through gills.
locust head
thorax
jointed leg
wing
antenna 1 cm
edible
crab,
Cancer pagurus
abdomen
moth
exoskeleton containing calcium salts eye
2 cm
claw antenna
jointed leg
Arachnids These are the spiders, ticks and scorpions. They are land-dwelling organisms.
Myriapods These are the centipedes and millipedes. Characteristics: l body consists of many segments l each segment has jointed legs.
Characteristics: l arthropods with four pairs of jointed legs l breathe through gills called book lungs.
centipede
long, thin segmented body
spider,
Araneus diadematus jointed legs on each segment eye cephalothorax 2 mm abdomen
pedipalp 4 pairs of jointed legs 0.5 cm
Figure 1.6 Classification
of
arthropods.
6
IGCSE
Biology