Why wont the professor let me take that class?

it's a 400-level class but it doesn't have any pre-requisites. I registered and then the registration office emailed me to tell me that my registration for the course has been removed. I asked why and they told me to contact the professor or the department chair. I emailed the professor and he said you have to be a senior to take that class and I'm not so that's why he removed me from the registration list, and offered it to someone else. I want to talk to the department chair now, because it doesn't say anywhere on the bulletin or on the registration website that this course requires students to be seniors! I want this class for my major and my adviser even told me to take it! It's in the Arts department. Can any of you help?