Notochord is present throughout life in which of the following?

Explanation

All animals belonging to Phylum Chordata have three things in common which are as followed: 1: Notochord 2: A dorsal hollow nerve cord 3: Pharyngeal Gill Slits. The question deals with knowing the animal in which notochord persists through out life. Since, Notochord is replaced by Vertebral Column in higher animals thus, option 'B' and 'C' are eliminated immediately. Option A: It deals with Urochordates which contain Notochord in the small region of it's tail, which is consumed ultimately after a time, thus marking it incorrect. Option D: Cephalochordates have a Notochord which extends right in the mid of the dorsal line from anterior to posterior part of the body. In Cephalochordates, Notochord isn't replaced by vertebral column, and thus this is the correct option.