Arthropod

Arthropods are a very large group of animals without backbones, called invertebrates. They have a hard outer shell, called an exoskeleton, made of a special material called chitin, and their bodies are made of many parts that repeat in patterns. They also have pairs of jointed parts that help them move. Because their exoskeleton cannot grow with them, arthropods go through a process called moulting, where they shed their old shell to grow a new one.

Arthropods have many different kinds, with up to ten million known species. They have a special kind of fluid called haemolymph that moves around their bodies instead of blood. Their nervous systems are like ladders, with parts called ganglia in each body segment. They also have different ways to see, breathe, and take care of their young, depending on the species. Some arthropods can see very well with special eyes, while others use sensors on their bodies to feel their way.

Arthropods have been around since the Cambrian period, a very long time ago. Today, they are very important to our world. Many crops depend on arthropods like pollinators to help them grow. However, some arthropods can spread diseases that affect people, animals, and plants.

Etymology

The word arthropod comes from ancient Greek, meaning "jointed leg". It was first used in scientific writing in 1843 by a German scientist.

People often call land arthropods "bugs". Sometimes this word is used for certain water creatures, but scientists only use "bugs" for a specific group of insects.

Description

Arthropods are animals with bodies that have segments and jointed limbs. They have a special outer covering called an exoskeleton, which is made of a material called chitin. This exoskeleton helps protect them and gives them shape.

Arthropods are very diverse and make up a large part of all known animal species. They live in many different places, including water, land, and air. Some of the smallest arthropods are tiny crustaceans, while the largest can be quite big, like the Japanese spider crab.

The bodies of arthropod babies start with many similar segments, but as they grow, these segments change and group together in different ways. This is why insects have a three-part body, and spiders have a two-part body. Arthropods also have special body parts at the front and back that are not part of these repeating segments.

Arthropods need to grow, but their hard exoskeleton doesn’t stretch. So, they go through a process called moulting, where they shed their old exoskeleton and grow a new one. This happens many times as they get bigger.

Arthropods have different ways to breathe and move around. Some small ones can get enough oxygen just through their skin, while others have special parts like gills or tubes to help them breathe. They also have a simple circulatory system and different ways to remove waste from their bodies.

Arthropods have many sensors to help them sense the world around them. They can feel touch, smell, and even see. Many have special eyes called compound eyes, which are made of many tiny parts that work together to give them vision. Some can even see colors and details, while others are better at detecting movement.

Reproduction and development

Some arthropods, like barnacles, can have both male and female parts, but most stay one sex their whole lives. Many insects and small sea creatures can make babies without father help when there are lots of them, but usually they need both a mother and a father. Most water arthropods let their babies grow outside their bodies, but land ones keep them inside until they are born.

Most arthropods lay eggs, but some, like scorpions, give birth to live babies. Baby arthropods look very different when they first hatch. Some look like tiny adults right away, while others, like butterflies, start as worms and change into their grown-up shape later. Dragonfly babies live in water and have arms and jaws but cannot fly. Small sea creatures often start with just a few body parts and legs.

Evolutionary history

Arthropods are animals with jointed legs and a hard outer shell called an exoskeleton. They have a long history on Earth, with some of the earliest examples found in ancient rock layers.

Scientists believe the first arthropods had a simple body with repeating segments, each with a pair of legs. Over time, these animals evolved into many different groups, including spiders, crabs, and insects. Some early arthropods lived in the sea, while others were among the first animals to walk on land.

Fossils show that arthropods have been around for hundreds of millions of years. They have changed and adapted in many ways, but they all share the basic features that define arthropods today.

Interaction with humans

See also: Insects as food

Some arthropods, like crabs, lobsters, crayfish, shrimp, and prawns, are commonly eaten by people. Insects can also be a good source of food, and in many places they are eaten both raw and cooked. For example, tarantulas are a special treat in Cambodia and among the Piaroa Indians in Venezuela once their hairs are removed.

Arthropods also help humans by pollinating crops, which is very important for growing food. Beetles make honey, which is used in many foods and drinks around the world.

Some insects have been used to make useful products. For example, a red color called cochineal comes from a type of insect and was very valuable to ancient peoples. Shellac, made by insects, is used in woodworking and as a food additive. The blood of horseshoe crabs helps scientists check if medical tools are clean and safe.

Arthropods can also help scientists understand how robots can move. Their simple body shapes and ability to walk on different surfaces inspire new robot designs.

Even though many arthropods can bite or sting, most do not harm humans seriously. However, some diseases spread by insects can be dangerous. Some arthropods also harm crops and livestock, so people work to control them using different methods, including natural ways to keep pests away.