Chapter 27, Problem 28A

Summary Introduction

To write: The reason why there are no freshwater 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

Every chordate has some sort of a thyroid gland. They have a coelom and are segmented. Invertebrate chordates refer to two of the chordate subphylae- Cephalochordata and Urochordata. Hermaphrodites are predominantly tunicates. Within the body of the adult tunicate tunicate larvae hatch from eggs. A tunicate larva swims for a few days after hatching, before it finds a suitable surface to which to stick, usually in a dark or shaded spot. It then connects to the surface through the head and undergoes metamorphosis into the adult form, at which stage the notochord, nerve cord, and tail vanish. Most tunicates survive on the ocean floor a sessile life and are suspension eaters. Plankton and detritus are the main tunicate foods. Seawater reaches the body of the tunicate via its incurrent siphon.