Chapter 28, Problem 18STP

Summary Introduction

To write:

The circulatory systems of lancelets and tunicates and to classify them as invertebrate chordates.

Introduction:

Lancelets and Tunicates both belong to phylum Chordata.

Lancelets have a segmented body whereas Tunicates have myomeric segmentation.

Explanation of Solution

 A) The circulatory system of Lancelets:

• Lancelets are those marine organisms that belong to sub-phylum Cephalochordata and is non-sessile in nature.
• The circulatory system is simple but with no heart who transports food in the body.
• They live under the sand and are in need of warm temperature and tropical seas.
• They are blade shaped animals and are the closest living member of vertebrates.
• They have notochord which extends from the head region.
• They do not develop any bony skeleton.

 B) The circulatory system of Tunicates:

• Tunicates are those marine invertebrates whose outer coat is hard and rubbery.It belongs to the sub-phylum Urochordata .
• The circulatory system is well developed with a heart.
• They thrive in a dark and shaded locations.
• They are barrel-shaped animals.
• The larva forms distinctive features of chordates and adults have pharyngeal slits. Notochord is absent in adults.
• They contain cellulose like carbohydrate material, which covers their body.

Conclusion

Thus, chordates have two species, they are: Lancelets and Tunicates. They are invertebrates because they don’t have backbone.