ARTHROPODS

Insects, spiders, crabs, and lobsters are all arthropods, so there are a lot of arthropods on Earth. The earliest arthropods on Earth developed about 550 million years ago.

History

Their ancestors were a kind of worm that was divided

into segments, probably distantly related to annelid

worms. These worms probably had two antennae on

their heads, and a pair of eyes. They probably had

several head segments, at least one body segment

with several pairs of legs, and a tail segment.

Then these worms developed hard exoskeletons and became the arthropods. This hard shell protected them and helped them to survive. But their shells don't grow along with them, and so all arthropods have to shed their shell as they get bigger and grow a new one. Because of this most arthropods don't get very big.

Most of them are tiny insects or spiders, although some crabs and lobsters can weigh up to about twenty pounds.

Around 350 million years ago, some of the insects living on land began to fly, like modern flies or dragonflies or grasshoppers. When flowering plants appeared, about 200 million years ago, some arthropods, like bees, evolved to eat their pollen, and the bees and the flowers worked out a relationship that is good for both the bees and the flowers, where the bees help the flowers to reproduce.

Classification

Arthropods are divided into four main groups: Insects

Spiders

Crustacreans

Millipeds

Arthropods are a very diverse group, but they share some basic characteristics:

All arthropods have jointed legs and a head and segmented body parts called the thorax and abdomen.

An arthropod’s body is covered by a shell or a hard outer skin called an exoskeleton. It is made of a material called chitin.

Importance of Arthropods

Life on Earth would end very quickly without arthropods. Arthropods are great recyclers and decomposers and they are a super food source. They also help pollinate the plants that provide food and keep the air and water clean.

Crustaceans

A crustacean is an arthropod that has a hard, exoskeleton, two pairs of antennae, and a mouth for crunching and grinding.

Crustaceans can re-grow certain parts of their body.

Most crustaceans live in water and get oxygen from the water through gills.

Centipedes & Millipedes

Centipedes: Have one pair of legs in each segment Are carnivores and eat other animals To capture its prey, centipedes poison their

prey with their claws Centipedes are found in wet places like

under rocks and in the soil

Millipedes Have two pairs of legs for each segment Eat plants When scared, they roll up into a small ball

to protect itself Do NOT have claws Live in wet places such as under rocks and

in the soil

Spiders

Spider, ticks, scorpions, and mites ALL have 8 legs Their bodies are divided into a HEAD

region, CHEST, and STOMACH

Spiders

Most spiders eat bugs (insects), while some can eat very small vertebrates such as hummingbirds

Spiders make webs of silk. Silk is a thread material that is made in a spider’s stomach.

Spiders

Spiders can catch their prey in a few ways:

By trapping them in webs

Hide from their prey and them jump out

and catch their prey

Bite the prey and poison it

Insects

There are more insects in the world than there are total animal species all together

Insect bodies are divided into 3 parts: HEAD, CHEST and STOMACH

Insects have 6 legs

Insects go through METAPHORESIS

Insect Defense

Insects can protect themselves using stingers, or camouflage