Mrs Gren, living things

MRS GREN-7 Living Processes for a Crab.

Movement.
Instead of walking forward on two legs, they move quickly sideways in a flurry with their multiple legs. Crabs move sideways for the same reason humans move forward: that's how their bodies were built to move crabs, on the other hand, have multiple legs and they're located on the sides of their bodies.

Reproduction
Decapod crabs are built like a folded-up lobster. The abdomen, which is equivalent to a tail, is folded up tightly underneath its body to form an abdominal flap.

Sensing 
Like many other marine animals, crabs rely on their sense of smell to find prey. Crabs have chemoreceptors that allow them to detect chemicals in the water that are released by their prey a crab can "taste" using hairs on its mouthparts, pincers and even its feet.

Growth
This process is known as molting. They can live between 8–13 years and reach a size of 10-plus inches. Within 2-3 years, crabs are sexually active. At 4-5 years, they have grown to the legal harvest size (6 ¼ across the shell and 2-3 pounds in weight).

Respiration
The oxygen consumption, ventilation and blood gas transport were investigated in the tropical land crab Gecarcinus lateralis to determine the adaptations of the respiratory system for aerial respiration. The gills of Gecarcinus are reduced in size and specialized, in part, for salt and water uptake. The epibranchial space of the branchial chamber is very much enlarged and lined with what is probably a respiratory epithelium. There is a high ventilatory air-flow, produced by the beating of the scaphognathites, but the percentage extraction of oxygen is extremely low. This may be the result of ventilatory ‘shunts’, whereby a proportion of the air does not come into contact with the respiratory surfaces. The energetic cost of a high ventilation rate need not be high, because of the low inertial mass of air in comparison with water. A high oxygen tension gradient of 103 torr is maintained across the respiratory surfaces. This is interpreted as an adaptation to achieve a high oxygen diffusion rate through the reduced surface area of the gills. The blood has a relatively high oxygen capacity which is again thought to be an adaptation to compensate for the reduced gill surface area. Carbon dioxide tensions and content were high as in other terrestrial animals. Overall, the respiratory adaptations are thought to be related primarily to the reduction in the respiratory surface area which has evolved to deal with the problems of water conservation in these terrestrial animals.

Excretion
They have green glands in their second antennae that they use to get rid of some body waste. They also have a two-chambered stomach with a special grinding mill that grinds up food. They excrete most of their body waste though an opening on their telson. The telson is the last segment on their body.

Nutrition
Rich in vitamins and minerals, crab meat is also low in fat and contains Omega-3 polyunsaturated acids. Helps provide protection from heart disease and aids brain development. Some research suggests that Omega-3 also inhibits aggressive behaviour. And it's not just any old Omega-3 – it's the long chain variety.