What would you call an animal that doesn't eat plants, but doesn't eat meat? (Easy 10 points)?

I'm doing a school project and one of the animals I'm "investigating" is a species of sea lemon. It eats mainly sponges, and from my knowledge (most likely I'm wrong), sponges aren't plants (they're in the ANIMAL kingdom), nor meat. So what would you call this? (Like you call meat eaters carnivores, plant eaters herbivores and something that eats both an omnivore). Help please! 5 stars/10 points to first correct answer.