The correct option is B Notochord
Invertebrates are animals which do not possess a notochord. Examples include earthworm, cockroach, starfish etc. Chordates are animals that possess a notochord. It includes sea squirts, fishes, amphibians, reptiles, birds, mammals etc. Among the higher chordates, the notochord gets replaced by the vertebral column. These organisms are called vertebrates. Vertebrata is a sub-phylum under Phylum Chordata.