American lobster

American lobsters are invertebrates belonging to the Arthropoda phylum along with insects, spiders, and other creatures having an exoskeleton in place of a backbone. Lobsters, crabs, shrimps, copepods, and other similar species are divided into the Crustacea subphylum because of their flexible shells, differentiating them from hard and brittle-shelled creatures such as oysters, mussels, and clams. Lobsters are further placed in the order Decapoda because of their ten feet. American lobsters are located in the infraorder Astacidea which contains only marine lobsters and freshwater crayfish. These creatures are distinguished from other lobsters because they bear pincers on their first three pairs of legs, the first being the largest. They are again subdivided into to lobsters the Nephropidae family, which contains lobsters used mainly for commercial purposes.

Life cycle
American lobsters molt two to three times per year while juvenile, but only once a year or less often when fully mature, which is about four to seven years old. When a lobster nears its next shedding period, it will start to grow a new shell underneath the current one, and the outer shell will become very hard and darken. The line that runs along the back of the lobster's carapace will begin to split, and the two halves of the shell will fall away. Claws and tail will be pulled out from the old outer shell, as the inner shell is very malleable. The old shell is often eaten for calcium recovery and the leftovers are sometimes buried.

A scuba diver in New York's Wreck Valley displays his lobsters.
Females usually mate right after molting, but mating in between molts, known as intermolt mating, can occur. Larger females can store sperm for several batches of eggs from a single coupling. All females store the sperm to fertilize eggs later, not at the time of copulation. While getting ready to molt the female will find the den of a suitable male and visit it several times. When finally ready to molt the female will do so in that den. After the molt the male will wait for the shell to start to harden, gently stroking the paper thin new shell with his large antennae. After several minutes the male will raise himself on his claws and tail, then use his legs to flip over the female and get on top. The male has a pair of hardened swimmerets, or fins on the bottom, that match a pair of swimmerets on the female which have an opening between them. The sperm, contained in a gelatinous blob called a spermatophore slides down notches in the male's swimmerets into the female. The outside end of the spermatophore hardens to block the hole. The receptacle on the female is part of her shell so she will need to use the sperm before her next molt or lose it. The male dismounts and then may eat the female's shell. The female will then stay in the den for several days while her shell hardens more. Lobsters do not mate for life, contrary to some myths.

Source : articlesbase