Chapter 27, Problem 18A

Summary Introduction

To write: The connections between the muscular tube that links the mouth cavity and the esophagus develop slits and are used for filter feeding in some invertebrate chordates.

Introduction: Chordates are species belonging to the phylum Chordata that at some stage during their development have four distinctive characteristics-a dorsal tubular nerve cord, pharyngeal pouches, a notochord and a postanal tail.

Explanation of Solution

In both embryos, paired structures called pharyngeal pouches attach the muscle tube which connects the cavity of the mouth and the esophagus. The pouches in marine chordates have slits leading outwards. These structures were initially used for filter feeding, and later formed into gills for water gas exchange. The pharyngeal pouches do not have slits in terrestrial chordates, and grow into other structures including the tonsils and thymus gland.