ARTHROPODS

Centipedes, millipedes, insects, crustaceans, and arachnids, including spiders, all belong to a super-group of invertebrates called arthropods. Arthropods are more numerous and varied than any other animal group.

WHAT FEATURES DO ARTHROPODS SHARE?

All arthropods have bodies divided into segments and covered with a hard EXOSKELETON. This tough casing is made of a protein called chitin, which is also found in human fingernails. The armor is flexible at joints on the legs, which makes arthropods nimble.

WHAT IS THE DIFFERENCE BETWEEN A CENTIPEDE AND A MILLIPEDE?

Centipedes are active hunters, while most millipedes eat plant matter. Also, centipedes have two legs per body segment. Millipedes have four. Centipedes and millipedes are collectively known as myriapods.

DO ALL CENTIPEDES HAVE ONE HUNDRED LEGS?

The word centipede means “100 legs,” but some centipedes have fewer than 100 legs, and others have more. Similarly, the word millipede means “1,000 legs,” but in fact no millipede has more than 750 legs.

ARTHROPOD CLASSIFICATION

Arthropods make up the largest phylum (group) in the animal kingdom. There are more than 900,000 named species divided into 13 classes:

Crustaceans
Insects
Arachnids
Centipedes
Millipedes
Sea spiders
Pauropods
Symphylans
Springtails
Proturans
Two-pronged bristletails
Three-pronged bristletails
King crabs

EXOSKELETON

An arthropod’s exoskeleton is a protective case and an anchor point for muscles. As well as being tough, it is waterproof, helping these creatures to survive in even the harshest habitats.

LOBSTER

The lobster’s hard exoskeleton supports and protects its body. Even delicate parts, such as the legs and antennae, are completely encased. The North Atlantic lobster is the world’s heaviest arthropod, weighing up to 44 lb (20 kg).

HOW DO ARTHROPODS GROW?

In order to grow, arthropods have to molt (shed their exoskeletons) every so often. They then expand their bodies before their new casing hardens. Arthropods are vulnerable while molting, so they look for a safe place to hide before they begin.

WHERE DO ARTHROPODS LIVE?

Arthropods occur in virtually every habitat, from the cold ocean depths to the hottest deserts. They can live through extremes that would kill most vertebrates. Scorpions, for example, can survive being frozen solid.

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Invertebrates

Copyright © 2007 Dorling Kindersley