Crustaceans are members of the Arthropoda family that includes spiders, scorpions and insects. They are covered in a hard horny shell or, more correctly, carapace. This shell is shed periodically as the creature grows evidence of which can be seen washed upon on shorelines. Generally speaking, it's a good idea to choose lobsters and crab whose shells are encrusted and obviously old, as the flesh will have had time to develop and fill the shell. A crustacean with a new shell will often be small and lacking in flavor an exception to this rule is the soft-shell crab.
Many crustaceans are available all year, but tend to be at their best in the summer.
When choosing a large crustacean such as lobster or crab, look for specimens that feel heavy for their size and have legs and claws intact. Ideally, they should be bought live, but if already cooked store in the refrigerator and eat as soon as possible certainly within 24 hours. These must be removed during preparation. The roe, also called coral, and liver, sometimes called tomalley, of the lobster should never be discarded. They are considered delicacies and can be used for delicate sauce.