[32] However, a study by Bob Elwood and Mirjam Appel of Queens University in Belfast, found that hermit crabs reacted to electric shocks. The maxillipeds are used to hold and tear food as well as for grooming. Crabs are in the subphylum Crustacea. Parts of the exoskeleton are hard and other parts are thin to allow movement. They are decapods, along with lobsters, crayfish and shrimps. Crabs vary in size from the pea crab, a few millimeters wide, to the Japanese spider crab, with a leg span up to 4 m (13 ft). Abdomen Hermit crabs are unique and entertaining pets. [15]:113–114, Once crabs have become juveniles, they still have to keep moulting many more times to become adults. The crab must then extract all of itself – including its legs, mouthparts, eyestalks, and even the lining of the front and back of the digestive tract – from the old shell. Even though hermit crab’s have gills, they can drown if kept underwater. [35] The evolution of crabs is characterised by an increasingly robust body, and a reduction in the abdomen. Gills Some species are eaten whole, including the shell, such as soft-shell crab; with other species, just the claws or legs are eaten. When preparing for moult, the old shell is softened and partly eroded away, while the rudimentary beginnings of a new shell form under it. [35], Numbers of extant and extinct (†) species are given in brackets. In many tropical areas with land crabs, these migrations often result in considerable roadkill of migrating crabs. In some regions, spices improve the culinary experience. Of the six "pages" of the book gills, the first has an operculum with genital openings and the other five have small sensory branches and gill leaflets. Biologybyme Recommended for you. Hermit crabs are unique and entertaining pets. In fiddler crabs, males have one greatly enlarged claw used for communication, particularly for attracting a mate. The fourth and fifth pair are small legs that are used to hold a crab inside his shell. Drop your spare change here... make a donation to help with conservation! It is still a subject of debate whether a monophyletic group is formed by those crabs where the female, but not male, gonopores are situated on the sternum. Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice – are not true crabs. Some eat plankton, some eat primarily shellfish such as clams, and some even catch fish. Cephalthorax Maxillipeds Crabs attract a mate through chemical (pheromones), visual, acoustic, or vibratory means.
Crabs tend to be aggressive towards one another, and males often fight to gain access to females. [16] Some crabs, notably the Portunidae and Matutidae, are also capable of swimming,[20] the Portunidae especially so as their last pair of walking legs is flattened into swimming paddles. Legs While the new shell is still soft, the crab can expand it to make room for future growth.

When fertilisation has taken place, the eggs are released onto the female's abdomen, below the tail flap, secured with a sticky material. Crabs are prepared and eaten as a dish in many different ways all over the world. There are three divisions to the body of the horseshoe crab: the prosoma , the opisthosoma, and the telson. [36] A similar change occurred, independently, with the female gonopores.

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