Hexapoda

Some bugs have six legs.

They have three body parts. The first part is the head. The middle part is the thorax. The last part is the abdomen.

The head has eyes and antennae. Antennae help them feel things. The thorax holds the six legs.

Most bugs have wings on their middle part. These bugs can be very tiny. They can also be quite long. They are very important to our world. They help plants grow and clean up the land.

Hexapods are a large group of animals. The name means "six legs." Most of them are true insects. Other types include springtails, coneheads, and bristletails.

These animals have three body parts. The first part is the head. It has eyes and antennae. Antennae are parts used to feel things. The head also has jaws for crushing or chewing.

The middle part is the thorax. It has three segments. Each segment holds one pair of legs. This makes six legs in total. Most insects also have wings on this part.

The last part is the abdomen. In most hexapods, all the segments are there at birth. But coneheads are different. They grow new segments as they get older.

Hexapods can be very small. Some are only 0.5 mm long. Others grow to over 300 mm. They are very important to our world. They help plants grow by moving pollen. They also help clean up the land.

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.

Hexapoda is a massive subphylum of arthropods. The name comes from Greek words meaning "six legs."

This group is the largest clade of arthropods. It includes most of the living arthropod species on Earth. Hexapods include the class Insecta, which are the true insects. They also include a smaller group called Entognatha. This group contains three classes of wingless arthropods. These are Collembola, known as springtails. They are also Protura, or coneheads. Finally, there are Diplura, or two-pronged bristletails. These animals are vital to life on land. They act as pollinators, scavengers, and predators.

Most hexapods follow a very specific body plan. Their bodies are divided into three main parts. The first part is the anterior head. The head is made of six fused segments. It also includes a presegmental acron. This acron usually holds the eyes. However, Protura and Diplura do not have eyes. The head also has several appendages. Segment two holds the antennae for sensing the world. Segment four has mandibles, which are crushing jaws. Segment five has maxillae, which are chewing jaws. Segment six has the labium, or lower lip. A projection called the labrum, or upper lip, covers the mouth.

In true insects, the mouthparts are called ectognathous. This means the mouthparts are exposed. In other hexapod groups, the mouthparts are endognathous. This means they are enveloped or covered. The antennae also vary between groups. Collembola and Diplura have segmented antennae. Each segment in their antennae has its own muscles. Insects have different antennae with only three segments. These segments are the scape, the pedicel, and the flagellum. Only the first two segments have muscles. The flagellum is the third segment. It is composed of many small rings called annuli. This is known as an annulated antenna.

The middle section of the body is the thorax. The thorax consists of three distinct segments. Each of these segments bears one pair of legs. This creates the six legs that give the group its name. Most hexapod legs have five segments. They are built for walking on land. Unlike some other arthropods, they do not have gill branches. In most insects, the second and third thoracic segments also hold wings. Scientists think wings might be related to crustacean gill branches. They might also be extensions of the body segments themselves.

The final part of the body is the abdomen. The abdomen follows different growth patterns. Most hexapods use epimorphic development. This means all segments are present when the animal hatches. However, Protura use anamorphic development. This means juveniles hatch with an incomplete number of segments. They add new segments each time they molt. This continues until they reach adulthood. The number of segments also varies by group. True insects usually have eleven segments. Protura have twelve segments. Collembola have only six segments, and sometimes only four. Abdominal appendages are usually very small. They are mostly limited to genitalia or sensory cerci.

Scientists have long debated how hexapods evolved. For a long time, people thought myriapods were their closest relatives. This was based on physical similarities. However, new studies in the 21st century changed this view. Recent research suggests hexapods are part of Pancrustacea. This means they are closely related to crustaceans. A 2002 molecular analysis provided more clues. It suggests hexapods split from fairy shrimps, or Anostraca. This happened near the start of the Silurian period. This timing matches when vascular plants appeared on land. Now, remipedians are considered the closest living relatives of hexapods.

Fossils help us see the history of these animals. One important fossil is named Strudiella devonica. It comes from the Devonian period. Some researchers believe it is an early insect. Others think it might be a decomposed crustacean. This fossil might help bridge a gap in the record. That gap lasts from 385 million to 325 million years ago. In 2023, scientists found another fossil at Castle Bank. This fossil is from the Ordovician period. It looks like a hexapod-like arthropod. More study is needed to confirm this discovery. These fossils help us understand how life moved to land.