You see, decapods are also a branch of crustaceans--all your friendly ten-legged crabs and lobsters. And crustaceans are arthropods. And the most awesome arthropods are undoubtedly the eurypterids. They're extinct now, but they once grew larger than humans. How is that not awesome?
Nobu Tamura www.palaeocritti.com
And one of my fave webcomics, Gunnerkrigg Court, has just announced that two of its characters, Bud and Lindsey, "are very distantly related to eurypterids and xiphosura." (Xiphosura is the group of arthropods that includes horseshoe crabs.)
Sadly the eurypterids never got quite as big as Lindsey.