Amazing arthropods
With more than a million species, arthropods
make up the largest phylum (main group) in
the animal kingdom. They were the first creatures
to walk on land, more than 400 million years ago.
INSECTS ARACHNIDS
CENTIPEDES AND MILLIPEDES CRUSTACEANS
HORSESHOE CRABS SEA SPIDERS
Insects have three pairs of legs, and a body made up of
three parts: a head, a thorax, and an abdomen. This
is the biggest group of arthropods; in fact, 90
percent of all animal species are insects.
Bugs, butterflies, bees, and beetles
are all insects.Arachnid bodies are made up of two parts.
They have four pairs of legs, and two pairs
of mouthparts: one set look like legs or
claws for grabbing prey, while the other
set form pincers or fangs for
stabbing and killing. They have
no antennae. Spiders,
scorpions, ticks,
and mites are
all arachnids.These arthropods have a long body
divided into many segments. Centipedes
have one pair of legs per segment and
millipedes have two pairs per segment.
Centipede means “100 feet” and millipede
means “1,000 feet,” but different species can
have between a dozen and 750 legs.Most crustaceans live in water—
including crabs, lobsters, shrimp,
and barnacles—although woodlice
live on land. The species can look
very different: a blue lobster grows
to 3 ft (1 m) long, but acorn
barnacles are a tiny(^1) ⁄ 2 in (15 mm) across.
While they look like crustaceans,
horseshoe crabs are actually
related to arachnids: they have
four pairs of legs, two pairs of
mouthparts, and no antennae.
These animals have scarcely
changed in the 300 million
years they have existed.
Sea spiders are not spiders
at all, although they do have
long, spiderlike legs. Most
have four pairs of legs, but
some have five or six pairs.
They have two pairs of eyes.
WING PATTERNS help some
species to hide and evade predators.
THE IMPERIAL SCORPION uses its
sting in defense and its claws to catch prey.
THE GIANT
DESERT centipede
has a painful,
venomous bite.
SEA SPIDERS live deep below the waves.
LIVE LOBSTERS range in
color, but most are bluish-brown.
They turn orangey red when they
are cooked.
HORSESHOE
CRABS are close relatives
to extinct trilobites.
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There are as many
arthropods on Earth as all
other animals put together.
7
/^7
LIVING WORLD