1. Amphibians

2. What is an Amphibian?
The word amphibian means “double life”, because these animals live both on water and on land during their life.
They are vertebrates that live in water as larva and on land as adults. The adult form breathes with lungs, has moist skin and do not have scales and claws.

3. Form and Function in Amphibians
In frogs, tadpoles are filter feeders or herbivores that eat algae. The tadpoles will eat constantly.
As a tadpole becomes an adult it will only eat meat. They eat anything they can catch and swallow.
In their digestive system they have a mouth, stomach, small intestines (where food is absorbed), tubes to connect the liver, pancreas, and gallbladder to the intestine to help in digestion, and then the small intestine leads to the large intestine. At the end of the large intestine is the cloaca where digestive waste, urine, eggs or sperm exit the body.

4. Respiration
For larval amphibians, gas exchange takes place through the skin and gills. Lungs will replace gills in adults, but gas exchange still also takes place through the skin.
Many salamanders do not have lungs, so all of their gas exchange takes place through their skin.

5. Circulation
They have a double loop system. The first loop takes oxygen-poor blood from the heart to the lungs and skin, then takes the oxygen-rich blood back to the heart. The second loop takes oxygen-rich blood from the heart to the rest of the body and brings oxygen-poor blood from the body back to the heart.
The heart has 3 separate chambers: left atrium, right atrium, and ventricle. There is some mixing of oxygen-poor and oxygen-rich blood in a three chambered heart.

6. Excretion
Amphibians have kidneys that filter waste from blood.

7. Reproduction
Amphibians eggs must be kept moist, so many amphibians lay eggs in the water. Fertilization is external.
Metamorphosis takes place after the egg hatches. The egg forms a tadpole that can only live in water. The tadpole will grow limbs, lose their tail and gills. Eventually they will become a land dwelling adult.

8. Movement
Adult amphibians use their front and back legs to move. Frogs and toads can jump long distances. Some amphibians have suction cups on their toes for climbing.

9. Response Amphibians have well developed nervous and sensory systems.
Amphibians have large eyes that are protected from damage under water and kept moist by a clear nictitating membrane – this is movable and located inside the regular eyelid.
Amphibians have good eyesight so they can see and respond to moving insects. They cannot see in color.
Amphibians hear with a tympanic membrane (eardrums).

10. Groups of Amphibians
There are 3 main groups: salamanders, frogs and toads, and caecilians.

11. Salamanders
This is the order Urodela – includes salamanders and newts. They have long bodies and tails. Most have 4 legs. Both adults and larvae carnivores. Adults will be found in moist woods under rocks and rotting logs.
Some salamanders have gills and live in water all of their life.

12. Frogs and Toads
This is the order Anura. They all can jump. Frogs have long legs, but toads have short legs and can only make small hops.
Frogs need to be close to water their whole life. Toads can live in moist woods and even desserts.

13. Caecilians
Order Apoda. These are legless amphibians that will live in water or burrow in moist soil. They eat small invertebrates like termites.

14. Importance of Amphibians
Most amphibians must live in wet environments. Very few live in desert areas .
Many birds and mammals eat amphibians. But to protect themselves many are camouflaged. Many toads are unpleasant tasting or produce poisons.
For some reason amphibian populations have been declining. It is not known really why.