Crabs-Brachyura

These aren't the ones you find in spiral shells (hermits), the creepy ones with massive claws (porcelain), the crazy soldier like crustaceans (horseshoe), or the microscopic critters that live in pubic hair (or any course hair). These are the true crabs.

They have a thick external skeleton, two claws, live in the ocean, fresh water, and tropical land.

They can be a few millimetres wide (the Pea Crab), or up to 4 metres wide (the Japanese Spider crab).

Males have larger claws and a skinnier, pontier abdomen pouch on their belly, the female's is wider so she can fit her eggs in it whilst fertilising.

Crabs tend to mate belly-to-belly, and attract each other through hormones, dances, vibrations, or sounds.

They usually mate soon after the female has moulted her shell and is still soft. She can store the sperm for a long time before she choses to fertilise it.

When a female is carrying eggs, it's called "berried" because the eggs resemble little berries.

Throughout a crab's lifetime, it will moult many times. It's old shell starts to erode around it's body, while the new shell starts to form underneath. The crab will absorb large amounts of water to crack the old shell and spend hours if not days removing every part of it's body from the old shell. If it gets stuck, it has no chance of survival. 

After releasing the shell, it hides until the new shell it hard enough for protection.

They walk sideways because of the way their legs are laid out, but some can walk forwards and backwards, some can swim, like the paddle crab, who's back legs are flattened into little paddles to help.

Crabs make up 20% of all crustaceans caught by fisheries, and about 1 1/2 million tonnes are caught each year.