Different Types of Crab (with Pictures)

Crabs are one of those creatures that fire the imagination. They are alien and monstrous in some settings. They are fun and cute in others- who can resist a hermit crab?

If we look at the stars there is a whole constellation named in honor of these animals.

Certain crabs can also make a very tasty meal!

This page takes a look at some the most interesting types of crabs and how they live. It is not so much an exploration of the different families of crabs as an examination of what kinds of places crabs live with examples of individual species.

There is also an overview of the species that are most importent to human beings- whether as food, pest or simply as objects of curiosity.

What Makes a Crab

The typical crab:

• has ten jointed legs. (they are decapods)
• the front two legs are usually claws- sometimes, one of these will be massive and fearsome
• has two eyes on stalks
• breathes through gills which will work in water or air (as long the gills stay moist)
• has a hard shell (sometimes called an exoskeleton)
• grows by molting its old shell and then 'inflating' a new, bigger shell
• produces eggs that often the female will carry until they hatch into tiny larvae. These larvae will take their chances feeding in the sea before becoming adult crabs.

Crabs of the Sea Shore (Littoral Crabs)

The sea shore is one of the best places to find crabs. They are good at coping with the constant changes that the tides bring to sea shores. A crab can breathe underwater but can also breathe out of water for long periods. Whether the tide is in or out, these animals can survive.

Crabs need to cope with threats from the air, land and sea. Birds will eat them, fish will eat them, even people will eat them.

The crab's tough shell and spines provide some defense against predators. They are also good at hiding during daylight hours and at low tide. Some will bury themselves in sand or mud. Some hide in rock pools. Others retreat into the water as the tide ebbs.These behaviors stop them drying out, as well as being eaten.

Pictured right is the Rock Crab (or Maine Crab) that you find along the eastern coast of the US. It makes good eating.

In the UK, the Edible Crab (Cancer pagurus) is sometimes found on shore but is more common just below the waterline and to depths of 100 meters

Below is a video of a Striped Shore Crab (common on the West coast of America) scavenging for food on a rock. Like most crabs, this crab will eat any food it finds (they are omnivores). This includes algae, worms, mollusks, clams and even fungi.

Swimming Crabs

Many swimming crabs make good food. The Blue Swimmer Crab (Portunus pelagicus) is one example that lives mainly in river estuaries in Asia and Australia.

It buries itself in mud or sand as it waits for the high tide then emerges and swims strongly in search of food. A pair of flattened legs at the back of the crab make great paddles.

It will eat shellfish, algae and small fish. The video below shows a Blue Swimmer Crab eating a clam.

I can also tell you from personal experience that it makes a very fine meal. Crab Curry is a delicacy in many Asian countries.

A factsheet on Portunus pelagicus from Singapore: wildsingapore./portunidae/pelagicus

Oceanic Crabs

Christopher Columbus was the first European to come across crabs living in the middle of the Atlantic Ocean. The Columbus Crab (Planes minutis) clings onto weeds or other floating material like goose barnacles and, sometimes, even loggerhead turtles. It eats algae and invertabrates.

In the Pacific, there are 2 similar species- the Brown Pacific Weed Crab and the Blue Pacific Weed Crab. Not much is known about these creatures but they have the ability to change color to suit their backgrounds and escape being noticed.

They are quite small at around 3 inches across, fully grown.

Deep Sea Crabs

Some species are well suited to live in deep water.

Red King Crabs (Paralithodes camtschaticus) are an important food resource in Alaskan Waters and the North Pacific.

Often they are found on the sides of underwater mountains. They usually stay within a certain depth range and spread to other underwater mountains by producing swimming larvae.

The Japanese Spider Crab is another deep sea dweller and is able to live at depths of 600 meters.

Many deep sea crabs are very large!

Land Crabs

There are a few crabs that are entirely at home on land. Their gills are enclosed in water and they perform in a similar way to lungs allowing the crab to breathe efficiently. Most species need to return to the sea to breed.

One example is the Halloween Crab (Gecarcinus quadratus), pictured right, which can be kept as a pet.

There are many mangrove dwelling crabs of the genus Sesarma that can live very happily out of water. They do not even need to go back to the sea to spawn.

Invasion of the Land Crabs

In Caribbean countries, a common occurrence is an invasion of towns and villages by land crabs during their annual migration. Tens of thousands of land crabs head back to the sea to breed from the forests, choking roads and gardens. Many species of the most common land crab (scientific name Gecarcoidea) are toxic, so people do not eat them.

Coconut Crabs (Birgus latro)

These are the biggest land dwelling crab. They can weigh up to 4 kg (9.0 lb) and are about the size of a cat. They will eat almost any kind of food that they come across from fruit to dead animals. They are even capable of opening and eating a coconut, hence their name.

Plenty of details for the Coconut Crab: cookislands.bishopmuseum

Freshwater Crabs

There are many species that live in freshwater- especially in the streams and billabongs of Australia- but also every other continent.

The Southern European crab, Potamon fluviatile, pictured right, has been eaten by people since Roman Times.

Unfortunately, freshwater crabs are threatened by human activities more than most groups of animals and many species are in danger of becoming extinct.

bbc.co.uk/earth/