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Body
The lobster's body comprises two main sections. The cephalothorax -- which includes the lobster's head and mid-section -- comprises 14 fused segments that contain the lobster's legs and other appendages. It is covered in a hard shell called a carapace. The lobster's abdomen, also called the tail, includes six segments that aren't fused so the lobster can move.
Senses
Lobsters have one pair of large antennas and two pairs of small antennas. The lobster uses the large antennas for guiding itself through the environment. Lobsters use their smaller antennas, or antennules, for detecting chemical signals -- like odors -- that lead them to food. The lobster's eyes -- at the base of the antennas -- are made of thousands of tiny lenses. These eyes are so sensitive to light that lobsters are nearly blind in bright light. In low light, they help the lobster detect other animals' movements. Their eyes are protected by a beak-like structure called the rostrum.
Legs
Lobsters have five pairs of legs. Two pairs are used for walking and grooming. Two end in pincers used for handling and tasting food. The two front legs have claws. The lobster has one large claw called a crusher and a slightly smaller claw called the pincer claw. The crusher contains large teeth the lobster uses for breaking open its prey's shell. The pincer claw contains tiny teeth used for cutting. Like humans, lobsters exhibit "handedness." If the crusher claw is on the right side, the lobster is considered right-handed.
Mouth Parts
The lobster's mouth is behind the rostrum and just below the eyes. It consists of maxillipeds that bring food to the mouth opening and mandibles that tear it apart. However, food isn't chewed in the mouth. Instead, it is broken up in one of the lobster's stomachs. Lobsters also use their mouths for moving sand, gravel and small rocks when they burrow.
Internal Systems
The lobster's respiratory system comprises 20 sets of gills on either side of the cephalothorax. Lobsters absorb oxygen from water that passes through openings near the legs and over the gills. Lobsters have three stomachs: the foregut contains teeth that grind food into tiny particles, the mid-gut digests the particles and the hindgut expels particles too large to digest. Organs near the antennas' base expel waste. The lobster's circulatory system consists of a single-chambered heart with several openings that allow blood to flow in and out of nearby tissue. The heart beats 50 to 136 times a minute.