There are thought to be 113 different species of king crab living in the world's oceans. The three most common species, and the three most recognizable from commercial fishing, are the red king crab, the blue king crab and the golden king crab. All three species live in colder northern waters off the coasts of Russia, Japan and Alaska, where the largest populations are.
All king crabs have a very similar diet. Living on the ocean floor, they prey on smaller invertebrates that also habituate the sea bed. These include sea urchins and sea stars, barnacles, mussels, sea snails and clams. Younger individuals will feed on algae and zooplankton. King crabs of all ages will also feed on the remains of animals that die and sink to the sea bed, such as fish and sea mammals.
The king crab's mouth is on its underside below its eyes and antennae. To the sides are small adapted limbs, often called nippers, with which they tear food from its source and transport it to their mouth. They have several spiny plates ranged laterally inside their mouths which they use to "chew" the food.
Once of a suitable size, food particles pass from the mouth through the esophagus to the stomach, which is conical in shape. Here the food is further broken down by enzymes. It then passes to the intestines where the nutrients are extracted and, via the alimentary canal, through the liver (which is comparatively large considering the crab's size) for the filtering of toxins.
When all the possible nutrients have been extracted from the food particles, the remainder passes out of the king crab's body via two terminal ducts. These ducts are on the underside of the crab at the rear. The waste matter is called bile.