There's some show on TV called "Chopped" that my wife likes and I sometimes watch with her. The premise of the show is that four non-famous chefs are given random and usually weird ingredients and then have to cook a meal using all those ingredients (plus whatever else they want). Their meals are judged by famous/successful chefs. One person is eliminated (or "chopped) after each round, eventually resulting in a winner.
On a recent show, one of the ingredients was octopus. One of the chefs, a practicing Jew, said something about how she had no experience cooking with Octopus because she tries to keep kosher and doesn't use shellfish. I just wrote that off as a religious rule that wasn't based on scientific classification. But then another contestant commented that she didn't eat octopus because she's allergic to shellfish. That made me wonder...
So is octopus considered a shellfish according to the rules of Judaism? Does it have something in it that would react with people who are allergic to shellfish?