GENERAL HISTOLOGY

Detailed explanation-1: -Living species of chordates are classified into three major subphyla: Vertebrata, Urochordata, and Cephalochordata. Vertebrates are all chordates that have a backbone. The other two subphyla are invertebrate chordates that lack a backbone.

Detailed explanation-2: -Non-vertebrate chordates: Cephalochordata (lancelets), Urochordata (Tunicates), and Myxini (hagfishes) These groups are the chordates which do not possess vertebrae.

Detailed explanation-3: -So, the correct option is ‘Diaphragm’.

Detailed explanation-4: -All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These five synapomorphies include a notochord, dorsal hollow nerve cord, endostyle or thyroid, pharyngeal slits, and a post-anal tail.