Chapter 27, Problem 23A

Summary Introduction

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.

Answer to Problem 23A

Correct answer:

The correct answer is option (B) they have the same adult features as lancelets

Explanation of Solution

Explanation/justification for the correct answer:

Option (B) they have the same adult features as lancelets. Sea squirts are related to lancelets because sea squirts have all the features such as dorsal tubular nerve cords, pharyngeal gill slits, notochords, and postanal tails. So, the correct answer is option (B).

Explanation for incorrect answer:

Option (A) they are bilaterally symmetrical. The organism has identical body structure to that of a clam. Water is pulled into the body through an incurrent siphon; food particles are flushed out of the gill slits coated with mucus. The food then travels into the stomach, and then flows the waste material into the excurrent siphon. Adults lose 3 features of chordate as adults: Notochord, tail, and nerve chord nerve. So, this is an incorrect answer. Option (C) as adults, they have only one chordate feature. The notochord, the flexible tough cord, supported the animal, and also provided a place for attachment of muscles. With this configuration, chordates may swing their backs side by side and swim across the sea, a crucial advancement in chordate evolution. So, this is an incorrect answer.

Option (D) they are actively swimming predator. They are marine animals. Chordates may swing their backs side by side and swim across the sea, a crucial advancement in chordate evolution. So, this is an incorrect answer.