American lobster

A large decapod crustacean (having 10 legs), the American lobster, or Homarus americanus, is distinguished by its two asymmetrical claws: the one on the left, massive and serrated, is used for crushing, while the one on the right, thinner and sharper, is used to cut up prey.

The body is covered by a rigid carapace, usually a brownish-green color, but sometimes bluish or reddish. The abdomen ends in a telson and four large fan-shaped uropods. Although commercial lobster specimens are smaller, the species can reach a length of over 60 cm and weigh up to 9 kg.

Sexual characteristics are primarily visible under the abdomen. Males possess two pairs of rigid appendages called gonopods. These are situated at the base of the swimming legs, and are used to transfer sperm.

In females, these appendages are flexible and feathery, adapted for holding eggs. The female’s abdomen moreover is wider than the male’s, enabling her to carry the eggs she lays under her body. Finally, the crushing claw tends to be less voluminous in females than in males.

The lobster’s variable colors

The American lobster’s normal color is brownish-green, the result of a complex biochemical phenomenon involving a pigment called astaxanthin. That pigment, naturally red, gets transformed when combined with specific proteins contained in the carapace. The union modifies the structure of astaxanthin, which turns into crustacyanin. This takes on a blue tint, then yellow, depending on the layer. These three colors – red, blue and yellow – are distributed in overlapping layers in the shell, lending the lobster its characteristic brownish color.

When the lobster is cooked, the effect of heat denatures the proteins in the shell. The reaction between the proteins and astaxanthin breaks down. The pigment thus released regains its original color, that being bright red, which is why all lobsters, whatever their original color, turn red when cooked.