Classification

Question 1

Cnidarians (jelly fish) and echinoderms (star fish) were originally placed in the same phylum of Radiata because they all have radial symmetry. On what basis are they now in two distinct phyla?

Answer 1

Cnidarians have a very simple body structure lacking the deuterosome (second mouth) development seen in the echinoderms. Echinoderms also have bilaterally symmetrical larvae.

Question 2

List the major distinguishing characteristics of chordates:

Answer 2

A notochord (flexible rod shaped body in embryonic stage)
Ventral nerve cord
Pharynx pouches at some stage of development
An endostyle (produces mucus in the pharynx)to gather food
Metameric organisation (linear body segments)
Post- anal tail

Question 3

List the distinguishing characteristics of vertebrates:

Answer 3

A body plan with head
Trunk and post anal tail all supported by endoskeleton
Organ systems including a well developed brain and paired sense organs
A complete digestive system
An endocrine system
A closed circulatory system and excretion by paired kidneys
A body covering with many different adaptations
A neural crest in the embryo

Question 4

List the milestones in vertebrate evolution. How were these associate with the movement of vertebrates from aquatic to terrestrial environments?

Answer 4

Development of jaws/ enabled use of a much wider array of food sources
Growth of legs/ associated with movement on land of water
Development of the amniotic egg/ allows embryonic development within a protective shell that still allows oxygen transfer and provides embryo with an “aquatic” environment
Respiration using lungs/ internal lungs mean that the moist oxygen uptake surface is protected from dehydration compared to exposed gills
Increases in the number of heart chambers/ enables efficient use of lungs with separation if deoxygenated blood to be pumped to the lungs and oxygenated blood for circulation to tissues