Which of the following is a group of chordates only?

Correct answer. Doliolum, Pyrosoma and Amphioxus all are chordates. Chordates are the animals, which possess a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail for at least some period of their life. The phylum chordataU includes the subphyla Vertebrata, including mammals, fish, amphibians, reptiles, birds; Urochordata/ Tunicata, (including Herdmania- sea squirts, Doliolum, Pyrosoma)and Cephalochordata, comprising the lancelets(Branchiostoma). The phylum Hemichordata including the acorn worms was earlier considered fourth chordate subphylum, but it now is usually treated as a separate phylum. It, along with the phylum Echinodermata, including starfish, sea urchins, and sea cucumbers are nearest relatives of chordates.