Decapod

Many sea animals have ten legs.

This group includes crabs, lobsters, and shrimp. Most of them scavenge for food.

Some of these animals have big pincers. These pincers are used to help them eat. They also have many other parts on their bodies. Some have up to 38 parts in total.

There are nearly 15,000 kinds of these animals. About half of them are crabs. Many others are shrimp or hermit crabs. They live in many places in the sea.

Have you ever seen a crab or a lobster?

These animals belong to a group called decapods. The name comes from Greek words. It means "ten feet."

While they have ten legs, they can have up to 38 body parts.

Most decapods are scavengers. This means they eat bits of food found on the ocean floor.

Many have large pincers called chelae. They use these to grab food.

There are nearly 15,000 different species in this group. About half of them are crabs. Other members include shrimp, prawns, and hermit crabs.

Decapods are very old. Scientists think they began 455 million years ago. The oldest fossils date back to the Devonian period.

Many species grew as coral reefs spread across the sea. Scientists group them by how they look and how they grow. Some groups, like prawns, swim through the water. Other groups, like crabs, prefer to walk on the bottom.

Have you ever seen a crab or a lobster?

These animals belong to a group called decapods. The name comes from the Greek words for "ten" and "foot."

This group is very large and important to our oceans. It includes crabs, lobsters, crayfish, shrimp, and prawns. Most of these animals are scavengers. This means they look for bits of food to eat. There are nearly 15,000 different species living today. These species belong to about 2,700 different genera.

Decapods have a very interesting way their bodies work. They can have as many as 38 appendages. These are parts like legs or feelers attached to their body segments. Even though they have many parts, ten are called legs. These ten legs are called pereiopods. They are found on the last five segments of the chest. Many decapods have one pair of legs with big pincers. These pincers are called chelae. The legs that hold them are called chelipeds. They also have three pairs of maxillipeds to help them eat.

Scientists use fossils to learn about the history of these animals. The oldest fossils of this group date to the Devonian period.

A 2019 study used a molecular clock to look at their past. This study suggested decapods began around 455 million years ago. This was during the Late Ordovician period. The prawns, or Dendrobranchiata, were the first group to split off. Later, the remaining group split into swimmers and walkers. The walkers are called Reptantia and include crabs and lobsters.

There are many specific facts about how these animals are grouped. Scientists look at their gills and how their babies grow.

This helps them create two main suborders. The first is Dendrobranchiata, which includes prawns like the white shrimp. The second is Pleocyemata, which includes "true shrimp" and other groups. Many species grew quickly during the Jurassic and Cretaceous periods. This happened because modern coral reefs were spreading across the sea. These reefs provided a great home for many new species.

Decapods are part of a huge family of living things. You might see them at a beach or in an aquarium.

Some, like hermit crabs, live in shells. Others, like king crabs, are part of the Anomura group. This group also includes porcelain crabs and squat lobsters. There are about 3,000 species of shrimp in total. About 2,500 species are squat lobsters. Crabs make up nearly half of all decapod species. It is amazing to think how many different kinds live in the water.

Decapods are a diverse order of crustaceans found throughout the world's waters.

The name comes from the Ancient Greek words *dekas*, meaning "ten," and *pous*, meaning "foot."

This group includes many familiar animals like crabs, lobsters, crayfish, shrimp, and prawns. Most species in this order act as scavengers, feeding on organic matter. Today, scientists estimate there are nearly 15,000 living species belonging to about 2,700 different genera. This massive variety makes them one of the most successful groups of animals in the ocean.

The anatomy of a decapod is quite complex. While they can have as many as 38 appendages, these are arranged in pairs on different body segments. Only ten of these appendages are considered true legs, known as pereiopods. These are located on the last five segments of the thorax, or chest. In many species, one pair of these legs has evolved into large pincers called chelae. These specialized legs are known as chelipeds. Near the mouth, they also possess three pairs of maxillipeds, which serve as feeding appendages. The head area contains five pairs of appendages, including antennae and mouthparts. Finally, the abdomen carries five pairs of pleopods, and a tail fan is formed by the uropods and the telson.

Scientists classify decapods into two main suborders based on specific physical traits. They look at the structure of the gills and the way larvae develop to make these distinctions. The first suborder is Dendrobranchiata, which includes prawns like the white shrimp (*Litopenaeus setiferus*).

The second suborder is Pleocyemata, which contains "true shrimp" and many other groups. Within the Pleocyemata, many species belong to a clade called Reptantia. This group includes animals that usually walk or crawl, such as lobsters and crabs. This classification system helps biologists organize the thousands of different species into a logical tree.

The evolutionary history of decapods is very long. A 2019 molecular clock analysis suggested that decapods first appeared during the Late Ordovician period, about 455 million years ago. The Dendrobranchiata, or prawns, were the first group to diverge from the main line. Later, the Pleocyemata split into swimming shrimp and the crawling Reptantia. While their origins are ancient, the oldest physical fossils, such as *Palaeopalaemon*, date back to the Late Devonian. This shows that while the lineage is old, the fossil record captures their presence starting much later.

Decapods experienced a massive increase in species diversity during the Jurassic and Cretaceous periods. This surge in new species happened because modern coral reefs were rising and spreading across the oceans. These reefs provided essential habitats that allowed many different types of decapods to thrive. The relationship between the growth of reefs and the diversification of these crustaceans is a key part of marine history. This period helped shape the ocean ecosystems we recognize today.

The order is divided into many different groups with unique characteristics. Crabs are very successful, making up nearly half of all decapod species. Shrimp are also a massive group, with about 3,000 different species. Another large group is the Anomura, which includes hermit crabs, king crabs, porcelain crabs, and squat lobsters.

Squat lobsters alone account for about 2,500 species. This variety shows how the decapod body plan can be adapted to many different lifestyles.

Decapods are deeply connected to the broader health and structure of marine environments. As scavengers, they play a vital role in recycling nutrients within their habitats. Their presence in coral reefs shows how they are tied to the survival of other marine life. From the tiny shrimp to the large lobster, they occupy many different levels of the food web. Understanding their complex anatomy and long history helps us see how they have mastered life in the water over hundreds of millions of years.