Lobsters

Lobsters are a species of saltwater crustacean. A lobster was in a tank at The Hip Joint, and once spotted it, he instantly fell for it and they went home together. Later, Zoidberg was caught in a lobster trap with a few others, which escaped when busted Zoidberg out. Decapodians highly resemble these creatures, and thus Zoidberg is often called this when insulted.