The World’s Biggest Crustaceans!

What Are Crustaceans?

The word “Crustaceans” may sound like a long word to you, but this group of animals includes some very familiar ones. Crabs, lobsters, crayfish, shrimp and barnacles are all crustaceans. The crustaceans all belong to a larger group of animals, called Arthropods, which also includes insects, spiders and scorpions.

Where do Crustaceans live?

Most of them live in the sea or fresh water. Some of them are able to live on land, such as hermit crabs which some people keep as pets in an aquarium! Crustaceans have a hard shell to protect themselves from their enemy. Usually, their body is divided into two parts, a head and an abdomen. They have antennae which they use to sense the world around them, finding food or avoiding danger. The abdomen includes the heart, digestive system and reproductive system. They have strong legs for crawling and swimming. Many crustaceans uses their claws which help them to eat.

What kinds of crustaceans are there?

japanese spider crab
The Japanese Spider Crab is the World’s Biggest Crustacean, and in fact the world’s biggest Arthropod

Scientists group Crustaceans into  groups, which they call “classes”. These are

  • There are about 900 types of Branchiopods. These tend to be quite small – they look like little shrimps. They can survive in environments that other animals cannot, such as an almost dried-out lake. The famous “Sea-Monkeys” kept as pets are Branchiopods.
  • The 17 types of Remipedes are blind, and spend their time swimming upside-down on their backs at the bottom of the sea. They have a very complicated head, with a long trunk and fangs. Very little is known about them.
  • The Horseshoe Shrimps are small creatures that live in the mud on the sea floor. They eat by sitting still and whooshing water and mud into their mouths, hoping that something yummy will be washed in. Scientists call them Cephalocarida.
  • The Maxillopods have a small body and legs compared with their head. The most extreme are the Barnacles, which stick themselves permanently to any convenient underwater surface.
  • There are 13000 living species of Seed Shrimp. These tiny crustaceans make up part of what we call Plankton, so are important food for many sea animals. Others live on, or in the sea floor, or even in damp forests soil!
  • The last group (scientists call them style=”font-style: italic;”>Malacostraca) contains all the most familiar (and all the largest) crustaceans. There are
    • The tiny Leptostraca (the name means “thin shell”) live throughout the world’s oceans.
    • The Mantis Shrimps are not shrimps, but look like them. There are about 400 different species, the biggest can grow over a foot long (30 cm). They have very powerful claws, and are sometimes called “thumb splitters” or “prawn killers”.
    • Woodlice, pillbugs, crabs, lobsters, prawns and shrimp all belong to the third and final subclass of Malacostraca. Many of these are eaten by humans. All the biggest crustaceans belong to this group.

What is the world’s biggest crustacean?

The world largest crustacean is the Japanese Spider Crab. It can weigh up to 20kg (45 lb). If it stretches out its legs, they can reach up to 4 metres (13 feet) from tip to tip! It gets its name because its long legs remind people of an enormous spider.

On the other hand, the American Lobster (though smaller) weighs more than the Japanese spider crab. It can bulk up to weighs up to 22kg (48 lb) and measure almost 1.2 metres (1.3 yards) long.

Both the Japanese Spider Crab and the American Lobster live in the sea. The Coconut Crab, Birgus latro, is not just the largest land-living crustacean, it’s the largest land arthropod and the largest land invertebrate of all! It has a body that measure  up to 40 cm long (16 inches) and weighs up to 4 kg (8.8 lb). Its legs may span 1 m (39 inches). It gets its name from its favorite food.

The largest freshwater crustacean is the Giant Fairy Shrimp, Branchinecta gigas which has a body length of 15cm (6 inches). The largest barnacle is the Giant Acorn Barnacle, Balanus nubilis, reaching 7 cm (2.8 in) in diameter and 12.7 cm (5 in) high. The largest crustacean which stays in a cave is the species Godzillius robustus. It is 4.5 cm in length.

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