Handout 4-A

Lobster Parts

Armored Arthropod Lobster The first thing you notice about Homarus americanus, the "Maine" or "American" lobster, is its two strong claws: a big-toothed crusher claw for pulverizing shells and a finer-edged ripper claw resembling a steak knife, for tearing soft flesh. The lobster uses these claws, as well as smaller appendages around its mouth (mandibles and maxillipeds), for gripping and shredding its food. Besides its formidable front claws, the lobster also has eight walking legs, giving it ten legs altogether, which is why people who classify things call it a decapod.

The lobster usually crawls forward on its walking legs, but if it needs to make a quick exit, it contracts its tail forcefully and scoots backwards. When you first pick up a lobster, it frequently exhibits that flight response. Lobstermen call young lobsters, who do this a lot, "snappers." Under stress, a lobster may also "throw" a claw or a walking leg, but it will eventualy regenerate a new, fleshy, "limb bud." At the next molt, the lobster deposits a skeleton on the new limb. The lobster wears its skeleton on the outside (an exoskeleton), like a suit of armor. Because of this crusty covering, the lobster is included in the category of crustacean, along with crabs, shrimp, and barnacles. Crustaceans belong to a larger group known as Arthropods, which includes spiders, insects, and horseshoe crabs.

Sense-sational facts: chemoreceptors and other lobster senses

A lobster paces the ocean bottom in a shadowy world where vision is not all that important. Each eye, set on a movable stalk, has up to 10,000 facets that operate like many tiny eyes. The lobster probably doesn't see images, but its eyes can detect motion in dim light. In bright light, a lobster is probably blind.

Because of its poor vision, the lobster learns about its environment primarily through touch, taste, and smell. In fact, you could say the lobster's whole body is a sense organ. The long pair of antennae and tiny hairs that cover the entire body, including the walking legs, are sensitive to touch. Short bristles called "hedgehog hairs" line the insides of the pincers on the walking legs.

p.1 - Handout 4-A

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