One of the claws is called a shredder, I believe it's the smaller of the two, one crushes, the other shreds.

A lobster is called a shedder (no r) when it's in it's new shell. Lobsters shed their hard shells and have a soft shell for part of the year. The soft shell is larger (the lobster will grow into it) and there is a huge debate over which is better, a hard shell or a soft shell. Maine lobsters are for example coming in soft and hard shell now, soft shells usually run July to October. They sell for less because people don't like them as much, they don't think they are a good value (there is more space between the meat and the shell, so by weight there is a lot of water in them). It takes a couple of months for the shell to harden.

Personally, I love them both ways.

Males shed twice a year, females once usually.