Hexapoda

Hexapods are a huge group of animals. Their name comes from Greek words meaning "six legs."

This group is the largest part of the arthropod family. It includes true insects, which we see every day. It also includes smaller groups like springtails, coneheads, and bristletails. These living things are very important to our world. They help plants grow by moving pollen. They also act as scavengers to clean up the land.

Most hexapods follow a specific body plan. Their bodies have three main parts. First, there is the head at the front. The head has eyes and antennae for feeling. It also has jaws for crushing or chewing food. Next is the thorax, which is the middle section. The thorax has three segments. Each segment holds one pair of legs. This gives them six legs in total.

Many insects also have wings on the thorax. Finally, there is the abdomen at the back. In most groups, all abdomen segments appear during early growth. However, coneheads are different. They add new segments each time they molt.

Scientists have studied how these animals are related. For a long time, people thought they were close to myriapods. Myriapods are animals like centipedes. Later, new studies changed this idea. Now, it seems hexapods are closely related to crustaceans.

A study from 2002 used molecules to look at their history. It suggests hexapods split from fairy shrimps long ago. This happened near the start of the Silurian period. This was also when plants began to grow on land. Now, researchers think remipedians are their closest living relatives.

Hexapods come in many different sizes. Some are tiny, only 0.5 mm long. Others are much larger, growing over 300 mm.

Insects usually have eleven segments in their abdomen. Some species have fewer segments than that. In the group called Protura, there are twelve segments. Springtails, or Collembola, have only six segments. Sometimes they even have only four segments. Their antennae are also special. In insects, the antennae have three parts. These parts are called the scape, the pedicel, and the flagellum.

We can find clues about hexapods in old rocks. These are called fossils. One fossil named Strudiella devonica is from the Devonian period. Some scientists think it is an early insect. Others think it might be a decomposed crustacean.

In 2023, a new fossil was found at Castle Bank. This fossil looks like a hexapod from the Ordovician period. Scientists are still studying it to be sure. Finding these fossils helps us understand how life changed. It helps us see how animals moved from water to land.