1. Animals
continued

2. Vertebrates
Remember the list you created at the beginning of this section; how many of these animals have a vertebrate?
If your list of ten animals has more than one vertebrate, it is not consistent with what you would find in nature.
Of all the animals, vertebrates make up only 5% of the population.
Why are they the animals we think of first?

4. Classification
The animals you will explore belong to the phylum Chordata.
Not all animals in this phylum contain a vertebrate.
There exists a subphylum called Vertebrata which contains animals without a vertebrate which you will learn about.

5. All vertebrates have vertebrae (singular vertebra) which is a covering made of either cartilage or bone that protects the dorsal nerve.
In addition, all vertebrates have a large brain that is protected by a skull.
They have specialized tissues that form organs which are protected in a large coelom.
Vertebrates have advanced organ systems including circulatory, nervous, digestive, and reproductive.
In addition, they all have one or two pairs of appendages that aid in movement.

6. Fish
The most obvious characteristic about fish is their habitat. Of course you know they live in water, most species of fish live in salt water, like the ocean.
All fish have gills which are needed to exchange the waste product carbon dioxide and the much needed oxygen.
Fish are further divided into three classes: Agnatha (jawless fish), Chondrichthyes (cartilaginous fish) and (Osteichthyes) bony fish.
We will explore the characteristics of bony fish.

7. Bony Fish
Bony fish include trout, salmon, cod, perch, sole, eel, halibut and tuna and additional species.

8. Physical Characteristics
All bony fish start off with a skeleton made of cartilage.
As the fish matures, bone replaces the cartilage.
Scales cover and protect the body of the fish.
All bony fish have gills that are protected by a plate called operculum.

9. Movement of the operculum allows water to move into the mouth and out through the gills for gas exchange even if the fish is not moving.
The gills provide a large surface area to extract oxygen from the water.
Most bony fish contain swim bladders that are filled with air.
Fish can control their depth level by adjusting the amount of air in the swim bladder.
Diagram of a Bony Fish

10. Reproduction
Female bony fish secrete a large number of eggs outside of their body.
This is called external fertilization.
The male fish swim over the deposited eggs and release milt.
Milt is a fluid that contains sperm cells.
The fertilized egg cell undergoes the process of mitosis.

11. Recap on Dichotomous Keys

13. Create a dichotomous key that can be used to classify the six animals below.

14. Vertebrates vs. Invertebrates
List three differences between worms and fish.
Which characteristic of worms makes them similar to fungi?
What evolutionary advancement does the operculum provide?
Describe the process of gas exchange in worms and fish.
Why are vertebrates the type of animal we always think of first?
Further reading: