Chapter 27.2, Problem 1NV

Summary Introduction

To define:

The terms chordate, invertebrate chordate, notochord, postanal tail, dorsal tubular nerve cord, and pharyngeal pouch.

Explanation of Solution

Chordates are the animals that possess a notochord throughout their life or at some point in their life.

In some animals, the notochord is surrounded by bone or cartilage and result in the formation of a vertebral column. The animals that possess a vertebral column are called vertebrates.

Notochord: It is a rod-shaped, flexible mesodermal structure that is found in the embryonic stage of every chordate and also in the adult stage of some chordate species.

Post-anal tail: It is a posterior elongation of the body, that extends beyond the anus. It comprises muscles and skeletal elements, that help in the locomotion of various aquatic species, especially fishes.

Dorsal tubular nerve cord: It is located dorsally to the notochord in the chordates. It is derived from an ectoderm that rolls into a hollow tube at the time of development. The dorsal tubular nerve cord is one of the distinctive features of the phylum chordates. It develops into the central nervous system.

Pharyngeal slits are openings in the region just posterior to the mouth, called pharynx that extend to the external environment. It is an important structure in aquatic organisms as it allows the exit of water that enters the mouth at the time of feeding. The pharyngeal pouch is the cavity that links the nasal and the mouth cavity to the digestive system through esophagus.