Read the following characteristics of an animal: (i) It is exclusively marine. (ii) The notochord extends from the head to the tail region. (iii) The notochord is persistent throughout its life. Identify the subphylum to which this animal belongs and choose the correct example from that subphylum.

Step-by-step solution

The given characteristics describe an animal belonging to the subphylum Cephalochordata. Cephalochordates are exclusively marine protochordates in which the notochord extends from head to tail and persists throughout their life. Branchiostoma (Amphioxus or Lancelet) is a classic example of Cephalochordata. Ascidia and Doliolum belong to Urochordata, where the notochord is present only in the larval tail. Petromyzon belongs to Vertebrata (class Cyclostomata), where the notochord is replaced by a cartilaginous verteb