Crustacean

Many animals have hard shells.

These animals live in the water. Some even live on land.

They have a hard shell to protect them. As they grow, they must shed the old shell. This helps them get bigger.

Some are small, like tiny krill. Others are very large. The Japanese spider crab is huge. It has very long legs.

Many people eat shrimp and prawns. They are a very important food. These animals are truly amazing.

Crustaceans are animals with hard shells.

Most live in the water. Some live on land too. They belong to a group called arthropods.

These animals have an exoskeleton. This is a hard outer shell. It protects their bodies. To grow, they must shed this shell. This is called moulting.

There are 67,000 known species. Some are very small. The Stygotantulus stocki is tiny. Others are very big. The Japanese spider crab has a huge leg span.

Many crustaceans are food for people. We eat many shrimp and prawns. Krill are also very important. They are a big part of the food chain.

Most have bodies with three main parts. These are the head, the thorax, and the abdomen. Many have two-part limbs. These are called biramous limbs.

Young crustaceans often look different from adults. A common young form is the nauplius. This tiny stage has a single eye. It helps the young animal survive.

Crustaceans are a huge group of animals with hard shells.

The name comes from a Latin word meaning "those with shells." Most of these animals live in the water. You might know some, like crabs, lobsters, or shrimp.

Others include tiny krill or even barnacles that stick to rocks. They are very important to our world. Krill and copepods are a vital part of the food chain. Humans also harvest over 7.9 million tons of them every year.

How does a crustacean body work?

Their bodies have three main parts. These are the head, the thorax, and the abdomen. The head and thorax sometimes join together. This joined part is called a cephalothorax. A hard shell called an exoskeleton covers it. This shell protects the animal from danger. Because the shell is hard, it cannot grow. The animal must shed it to get bigger. This process is called moulting. They also have limbs that are divided into two parts. Scientists call these biramous limbs.

People have studied these animals for a long time. The name for the study of crustaceans is carcinology. A scientist who studies them is a carcinologist. Early writers like Pierre Belon used the name. Later, Morten Thrane Brünnich used the name "Crustacea" in 1772. Even famous scientists like Carl Linnaeus had different ideas about them. He once put them in a different group. Now, we know they are closely related to insects. This link is called the Pancrustacea group.

There are many amazing facts about their size and life.

We have described about 67,000 different species so far. Some are tiny, like the Stygotantulus stocki. It is only 100 micrometres long. Other animals are huge. The Japanese spider crab has a leg span of up to 3.8 meters.

Young crustaceans often look very different from adults. Many start as a tiny larva called a nauplius. This stage has a single eye and three pairs of limbs. They may also go through a stage called a zoea.

Crustaceans live in many different ways. Most swim or crawl in the ocean or fresh water. Some are even parasitic, which means they live on other animals.

A few have moved onto land, like woodlice. Even their eyes can be quite special. Some larvae have eyes that look like the water. This helps them hide from predators. This camouflage makes it hard for enemies to see them. It is a clever way to stay safe while growing.

Crustaceans are a massive group of arthropods known for their hard outer shells.

The name comes from the Latin word "crustacea," meaning "those with shells." These animals are incredibly diverse and play vital roles in global ecosystems. While most live in aquatic environments, some have adapted to life on land. They are essential to the food chain and human economies. Humans harvest more than 7.9 million tons of crustaceans every year for food.

This harvest consists mostly of shrimp and prawns.

The body of a typical crustacean is organized into specific segments. These segments are grouped into three main regions: the cephalon, or head; the pereon, or thorax; and the pleon, or abdomen.

In many species, the head and thorax fuse to form a cephalothorax. This region is often protected by a large, single shell called a carapace. To grow, these animals must undergo a process called moulting. This involves shedding their hard exoskeleton to make room for a larger body. Each body segment, or somite, is protected by a shell structure. This structure includes a dorsal tergum, a ventral sternum, and a lateral pleuron.

Crustaceans are distinguished from other arthropods by their unique limbs and life cycles. Most of their appendages are biramous, which means they are divided into two parts.

This is a key feature that separates them from insects or myriapods. The head segments usually bear two pairs of antennae and specialized mouthparts called mandibles and maxillae. The thoracic segments bear legs, which can be used for walking or feeding. Some legs are called pereiopods, while others are called maxillipeds. In certain groups like Malacostraca, the abdomen also carries appendages called pleopods. These specialized limbs allow crustaceans to succeed in many different environments.

The internal systems of a crustacean are equally complex. They possess an open circulatory system where blood is pumped into a body cavity called the haemocoel. A heart located near the back of the body handles this pumping. Interestingly, different groups use different pigments to carry oxygen. Malacostracans use haemocyanin, while copepods and barnacles use haemoglobins. For digestion, they have a straight tube that often includes a gastric mill. This structure acts like a gizzard to grind up food. Their nervous system consists of ganglia, which are clusters of nerve cells that act like a brain.

Life cycles in crustaceans often involve dramatic transformations. Most begin as a tiny larva called a nauplius.

This stage is characterized by a single eye and three pairs of appendages on the head. Many species then progress to a zoea stage. Zoea larvae swim using their thoracic appendages. Some even have spikes on their shells to help them swim in a specific direction. To stay safe, some larvae have eyes covered in a crystalline layer. This layer makes their eyes match the color of the surrounding water. This natural camouflage helps them hide from predators while they grow.

Scientists who study these animals are called carcinologists.

The study itself is known as carcinology. The history of naming these animals is quite long. Early naturalists like Pierre Belon and Guillaume Rondelet wrote about them. In 1772, Morten Thrane Brünnich used the formal name "Crustacea." Even Carl Linnaeus, a very famous scientist, once placed them in a different group called "Aptera." Today, we know they are part of a larger group called Pancrustacea. This group links crustaceans to hexapods, which include insects.

The scale of the crustacean world is truly vast. There are approximately 67,000 described species, though many more likely remain undiscovered.

They range from the tiny Stygotantulus stocki, which is only 100 micrometres long, to the massive Japanese spider crab. The Japanese spider crab can have a leg span of up to 3.8 meters. Beyond their size, they are also vital to the planet's biology. Krill and copepods may have the greatest biomass of any animal group. They serve as the most important bottom layer of the food chain in places like the Antarctic.