Chapter 16: Fishes, Amphibians, and Reptiles

SECTION 1

We have learned about animals without backbones, now we are going to turn our attention to animals with backbones. Animals with a backbone are called vertebrates. Vertebrates belong in the phylum Chordata. We call these organisms’ chordates. Vertebrates make up the largest group of chordates, but two groups (the lancelets and tunicates) do not have a backbone. The reason they are chordates is because they have a notochord (hollow nerve cord), pharyngeal pouches, and a tail at some point in their development.

The lancelets and tunicates are primitive chordates that live in marine ecosystems.

Organisms with a Backbone

The bones that make up the “backbone” are called vertebrae. The vertebrae cover the nerve cord for protection. The vertebrae have a hole (called a foramen) the nerve cord passes through. Vertebrates also have a head that is well protected by a skull. The skull and vertebrae are made of bone or cartilage. Cartilage is a connective tissue that is tough and flexible. Bones on the other hand are not flexible. Bone is very hard and can be fossilized easily.

Endotherm or Ectotherm?

Endotherm organisms produce their own heat for their body. Endo means within, therm means temperature. So, Endotherm means the temperature comes from within. Remember cellular respiration creates heat and the body of endotherms captures the heat to maintain a constant temperature. Endotherms are also called warm-blooded. Due to the fact that endotherms maintain a constant body temperature, they are capable of living in cold environments. Examples of endotherms: birds, deer, bears, cats, dogs, wolves, mice, and humans (these are only a few).

Ectotherm organisms are those that rely on the environment to supply their heat and maintain their body temperature. Ectotherms are also called cold-blooded organisms. Ectotherms examples include fish, reptiles (snakes, lizards), and amphibians (frogs and salamanders).

SECTION 1 Continued

Fishes

Fish are vertebrates and ectothermic organisms. Some fish are predators, and others are prey. Fish must search for their food so they are consumers. They have a brain and nervous tissues. Fish have fins, which are thin structures that help them to swim. Most fish also have scales on the surface of their skin for protection and reducing friction when they swim.

The Senses of Fish

Fish pick up vibrations and noises through an organ called a lateral line. The lateral line extends down the side of the fish from head to tail. The lateral line can help fish pick up vibrations given off by prey and if they are a prey species, they can detect the vibrations of predators.

Fish breathe though their gills. The anatomy of the gills is such that dissolved oxygen in the water can diffuse into the fish’s bloodstream. This same process (diffusion) also rids the fish’s body of carbon dioxide.

The majority of fish have external fertilization in which the female deposits the eggs into a nest in the water or simply into the water and the male releases sperm and the sperm and egg unite (fertilization) outside of the male and female fish. A few fish have internal fertilization in which the male deposits the sperm inside the female. Fish that carry out internal fertilization usually give live birth to their young. Example of live birth from fish is the common molly many people have in their home aquarium.

Types of Fishes

There are several types of fishes. One group has bones that make up their skeleton and another group has cartilage instead of bones and yet another group is called jawless fish.

Jawless fish do not have jaws. This group includes lampreys and hagfish. They resemble eels and have smooth, slimy skin. Their mouth is round and they attach to other fish and feed like a parasite on the nutrients from their host. They have a notochord, but do not have a backbone. They have a skull, brain and eyes.

Cartilaginous Fishes. Examples of this type of fish include sharks, skates, and rays. During their development from embryo to adult, their cartilage is not replaced by bone, but remains cartilage all of their life. These fish have a notochord and keen sense of smell and vision. They also have a lateral line system also. The skin of cartilaginous fish is covered with denticles which make the skin feel sandpapery if you run your hand from tail to head. If you fell of it from head to tail, the skin feels smooth. Some cartilaginous fish must swim all the time to keep water flowing across their gills or they will suffocate if they stop swimming. There is one cartilaginous fish called the paddlefish that live in freshwater in our area.

Bony Fishes. You are probably more familiar with bony fishes because most freshwater fish are bony fish. Examples include bluegill, bass, catfish, perch, goldfish and many other aquarium fish. These fish have bones for their skeleton as the name implies. Bony fish have the ability to remain in one place without swimming because they have a swim bladder (a balloon like organ filled with air). The swim bladder gives the fish buoyancy (the ability to float in water).

There are two groups of bony fish named due to the type of fins they have. One group is ray finned fish. Ray finned fish are the most common and they have paired fins that are supported by bones. The second group is called lobe finned fish, which have fins that are thick and supported by muscles. The lobe finned fish are considered representatives of ancient fish.

SECTION2 AMPHIBIANS

The majority of amphibians today are frogs and salamanders. Early examples or ancient amphibians looked a lot different from what we know as amphibians today. The unique feature of amphibians is the lung. This enables them to be land dwellers at times. They are capable of leaving the water and they breathe atmospheric air. Their skin must remain moist so they can not be away from moist environments for long periods at a time.

Amphibian Characteristics. Amphibian means “double life”. This refers to the fact that they must develop in wet environments, but as adults they are partially adapted to life on land. They must always live near water or moist areas. Most amphibians do not have scales, but they have smooth and slick skin. The organisms that make up amphibians are found in a wide range of colors. Many of the brightest colored amphibians are poisonous (like the poison dart frogs). Amphibians are unique because they have lungs, but they can also absorb oxygen through their skin because their skin is very thin and full of blood vessels.

The embryo of amphibians usually develops into a tadpole, which must live in water or very wet conditions. As the tadpole develops, they lose their tail and develop legs. The process of changing from the tadpole to the adult form is known as metamorphosis. A few of the frogs do not form a tadpole, but develop into frogs from the embryo stage.

Kinds of Amphibians. There are three groups, 1) caecilians, 2) salamanders, and 3) frogs and toads.

Caecilians are legless amphibians and many people are not familiar with these organisms. Caecilians live in tropical areas.

Salamanders – these are considered the most prehistoric amphibians. Salamanders eat small invertebrates. They survive in wet areas and many are colorful.

Frogs and Toads – This is the largest group of amphibians. They are found all over the world and in almost all environments. Frogs tend to have a more moist skin and toads are well adapted to dry climates. These organisms have a tongue that “flips” out and is sticky on the tip. The frogs and toads feed on insects. Many frogs and toads are capable of “singing” because they have vocal cords. The majority of their singing occurs when they are searching for mates.

All amphibians are environmental indicators because their skin is thin and they are sensitive to changes in their ecosystem. Many scientists are studying amphibians to determine what a “healthy” environment should be. If scientists notice problems in amphibian populations, there is a very good chance that some factor in the ecosystem causing the problem.

SECTION3 REPTILES

Many scientists believe that reptiles were the first animals to live out of the water and on dry land. Many also believe that there was a group called Therapsids that were the ancestors to the mammals.

Characteristics of Reptiles. Reptiles have thick skin and this serves as protection from their cells from drying out. Reptiles have lungs that enable them to survive on land. Reptiles are cold blooded (ectothermic) and become active as the environment they survive within warms up. As the environment cools down, their metabolism slows down.

Reptiles have an amniotic egg, which means it is an egg surrounded by a shell. The shell prevents the embryo from drying out. The reptile egg has yolk (food for embryo), albumin (protein source for the developing embryo), amniotic sac (surrounds the embryo and protects it from injury because the fluid inside act as a shock absorber), and the shell.

Most reptiles have internal fertilization and the shell develops around the egg and then the female lays the egg. Many lay their eggs and bury them under decomposing vegetation, which incubates the eggs as it decomposes (remember that heat is generated as material decomposes.)

Examples of Reptiles: Turtles, snakes, lizards, alligators, and crocodiles. Most turtles live their life near or in water, yet they have lungs to breathe air from the atmosphere. Turtles eat many invertebrates and some capture vertebrates as food sources. Crocodiles and alligators are carnivores (meat-eaters) and are effective predators and live in association to water sources. Lizards are found in most environments, and feed on insects, invertebrates and a few feed on vertebrates. Also, many lizards are herbivores. Snakes are carnivores, and many will consume eggs out of nests when they have the opportunity. Snakes swallow their food whole and have a jaw that can “unhinge” in order for their mouth to open wider and swallow their prey. Snakes have forked tongues and they have a organ that detects heat. When they have their tongue out they are taking a sample of the air because molecules will stick to the tongue and then taken into their mouth to the organ of sense. The organ is called the Jacobson’s organ.

SECTION 1 STUDY GUIDE

Animals with a backbone are called ______.
Vertebrates belong in the phylum ______.
The two groups of chordates that do not have a backbone are the ______and the ______.
The presence of a ______is what gives chordates their phylum.
______organisms produce their own heat from within their body.
______organisms rely on the temperature of the environment they are in to regulate their temperature. (Also called cold blooded.)

SECTION1 ContinuedSTUDY GUIDE

Fish are vertebrates and ______organisms.
Fish must search for their food, this makes them ______.
Fish sense vibrations through their ______line.
Fish obtain oxygen through their ______by diffusion.
The majority of fishes carry out ______fertilization for reproduction purposes.
Fish that carry out ______fertilization give live birth.
One type of fish that have bones are ______fish, while those that have cartilage are called ______fish and those without jaws are called ______fish.
Sharks, rays and skates have ______on their skin surface and that is why they feel sandpapery if you rub your fingers down them from tail to head.
Bony fish have a ______bladder that gives them buoyancy.
There are two types of finned fish which are ______finned fish and ______finned fish.

SECTION2 STUDY GUIDE

The majority of amphibians are ______and ______.
The three groups of amphibians are ______, ______and ______.
The legless amphibians found in the tropics are called ______.
______are considered the most ancient amphibians.
The largest group of amphibians is ______and ______.
When amphibians change from the tadpole to the adult stage, they go through the process known as ______.
Frogs have ______that allows them to “sing” or call for mates.
Amphibians are environmental ______because their skin is so thin and they are very sensitive to changes in the environment.

SECTION3 STUDY GUIDE

Many scientists believe that ______were the first animals to live out of water and on dry land.
Reptiles have ______skin that helps protect them from drying out.
Reptiles have a ______egg, which means it is covered or surrounded by a shell.
Most reptiles have ______fertilization, and many lay elongated eggs. The poisonous snakes in our geographical area give live birth.
Many reptiles rely on ______organic material to incubate their eggs.
Snakes have ______tongues that they sample the air with and then insert their tongue into the ______organ to “sense” their surroundings.
Snakes are ______, which means they are meat eaters.
The ______of the egg serves as food for the developing embryo.
Reptile body temperature is directly related to the temperature of the current temperature. This means they are ______or cold blooded.
In order for snakes to eat larger animals that normal, their jaws have the capability to ______.