Physical Differences
Shrimp are the smallest of the three, normally only a few inches long. Their shells are extremely soft, protecting a curved body. Shrimp also have at least a dozen small "legs" positioned directly underneath the body. Crabs have eight legs and one or two larger claws. Their bodies tend to be oval or hexagon-shaped with hardened shells on the top. Adult crab sizes vary greatly, from hermit crabs, which are 2 inches long, to king crabs, which can be a few feet wide. Lobsters are typically no more than 2 feet long and 1/2 foot in diameter, with curled bodies resembling shrimp housed under a hardened shell. However, lobsters have two large claws and a fan-shaped tail. They also have a set of 10 smaller legs positioned underneath the body.
Reproduction
Female shrimp can lay up to a million eggs that hatch within 24 hours. They can live up to six-and-a-half years. Crab reproduction consists of female crabs holding their eggs until they mate with male crabs. The female crabs store the sperm until the eggs are released to meet with the sperm. They are then housed in a spongy mass underneath the female until hatching. Lobsters tend to live near shorelines or the continental edges of all oceans. Females can lay anywhere between 8,000 and 100,000 eggs after carrying them to term for nine to 12 months. After hatching, baby lobsters hang on to the female for up to another year before releasing on their own.
Diet
Shrimp feed on plankton, algae and any other small organisms living near or on the bottom floor. Crabs are omnivores that eat seaweed and edible wastes. Smaller crabs will eat plankton and worms, while larger crabs eat shellfish, including shrimp. Lobsters usually eat at night on a largely carnivore diet. They sometimes scavenge from dead bodies, but lobsters prefer to eat fish, crabs, clams and other small crustaceans. Some lobsters will resort to cannibalism.
Consumption
Shrimp are pretty versatile when it comes to cooking. They are typically boiled, broiled, grilled, fried or even baked, with shells and veins removed or as whole pieces. Crabs are largely caught for their legs and claws, although crab meat is also removed from the body for consumption. Lobster tails and claws are a tasty dish and are the most expensive to eat in comparison.