The defining of characteristics of cephalochorates is ... ?

Answer

Its marine animal.

Explanation

Cephalochorates are small marine animal with unique features like segmented body and have notochord which are from head to tail and persist through out the life of this animal. They are present in modern oceans in form of lencelets which is also called amphioxus. They have hollow dorsal nerve chord and gill slits. Unlike the other vertebrates the nerve chord is never replaced by vertebrae