Another good topic from:
"Why Do Men Leave The Seat Up?"
"They don't have any happening nightclubs, Viagra, stiff drinks, or cheesy pickup lines. But that doesn't mean shellfish aren't 'getting lucky'. Oysters, mussels, clams, crabs, lobsters, shrimp, and thousands of other varieties of shellfish have their own unique mating techniques, some of which just might make you blush.
Take lobsters. When the female is ready for action, she releases a pheromone -- a chemical that has the effect of a sexy perfume -- into the den of the male she desires. He comes out of his bachelor pad aggressively and then returns to it with his new girlfriend. Eventually, the female molts, or sheds her hard shell, and the male gently turns her over for mating. The female stays in the male's den for about a week until her new shell hardens. (No word on whether he ever calls again.)
Crabs have a similar ritual; the female also molts before mating. However, this is preceded by a scene reminiscent of a frat party. The male tries to impress the female by standing on the tips of his walking legs and rocking from side to side. (Researchers have yet to determine whether he's wearing a toga.) Even if the female likes what she sees and accepts the invitation, she still plays hard to get for a bit. The male carries the female around for a few days before she molts. They then mate --brace yourself-- for a few hours. When they are finished, the male cradles the female until her new shell hardens. (Who says all men are pigs?)
As with crabs and lobsters, shrimp mate just after the female molts. When it comes to going for a roll in the seaweed, shrimp appear to be creatures of habit--not unlike some human couples, shrimp generally mate three times a year (in the spring, summer, and winter).
The mating habits of mussels, clams & oysters are downright wacky. With all three varieties, an adult male shoots sperm into the water. The target is, of course, a female, who is holding thousands of eggs in her gills. She catches all the sperm she can and then begins fertilization.
As this sexual sampling proves, shellfish might look like they're just sitting around, but that's hardly the case. Being encumbered by a shell hasn't stopped them from swinging.