1. By: Alice Tran and Kiara Hernandez
Chapter 30-3: Amphibians
By: Alice Tran and Kiara Hernandez

2. What Is an Amphibian?
“Amphibian” literally means “double life,” emphasizing that these animals live both in water and on land.
An amphibian is a vertebrate that, with some exceptions, lives in water as a larva and on land as an adult, has moist skin that contains mucus glands, and lacks scales and claws.

3. Evolution of Amphibians
Early amphibians evolved several adaptations that helped them live at least part of their lives out of water. Bones in the limbs and limb girdles became stronger, permitting more efficient movement. Lungs and breathing tubes enabled amphibians to breathe air. The sternum, or breastbone, formed a bony shield to support and protect internal organs, especially the lungs.
Some ancient amphibians were thought to be huge! So naturally, amphibians underwent major adaptive radiation.
Climate changes caused many of the low, swampy habitats in which amphibians lived to disappear, and many groups became extinct.

4. Feeding
Tadpoles: Usually filter feeders or herbivores that feed on algae and have long coiled intestines to break down hard to digest plant material.
Adult Amphibians: Carnivorous and have shorter intestines
In a frog, after food is broken down, it continues into the small intestine where the food is then absorbed. The small intestine leads into the large intestine/colon. At the end of the large intestine is a muscular cavity called the cloaca, where digestive wastes, urine, eggs, and sperm leave the body.

5. Respiration Excretion
Gas exchange through the skin and gills occurs in most larval amphibians.
Lungs usually replace gills when an amphibian becomes an adult.
UNLESS, the amphibian doesn’t have lungs at all, it then exchanges gas through the thin lining of the mouth cavity and skin.
Ex: some terrestrial salamanders
Kidneys: Filter wastes from blood
Urine travels through tubes called ureters into the cloaca.
Urine can either be passed outside or stored in a small urinary bladder.

6. Circulation
In most amphibians, the circulatory system forms a double loop.
The first loop carries oxygen-poor blood from heart to the lungs and skin and takes oxygen-rich blood back from the lungs and skin to the heart.
The second loop transports oxygen- rich blood from the heart to the rest of the body and carries oxygen-poor blood back to the heart.
An amphibian’s heart has three separate chambers:
An amphibian’s heart has three separate chambers:
Left atrium: where oxygen-rich blood from lungs and skin enters.
Right atrium: where oxygen-poor blood from body enters.
Ventricle: pumps blood to a single blood vessel (which branches out into smaller blood vessels) when it contracts.

7. Reproduction
Amphibian eggs tend to dry out easily, so the females lay the eggs in water, and the males come and fertilize them externally.
The male will climb onto the female’s back and squeeze. In response, the female will release up to 200 eggs, and the male will then fertilize them.
Frog eggs are encased in a sticky, transparent jelly that makes them difficult for predators to grasp.
The yolk of the egg nourishes the developing embryos until they hatch.

8. Movement
Response
Amphibian larvae move by wiggling their bodies and using a flattened tail for propulsion, like fishes.
Adult amphibians use their front and back legs to move in many ways.
Still others, such as frogs, have well-developed hind limbs that allow them to jump.
Amphibians have well-developed nervous and sensory systems.
Their large eyes can move in their sockets and are protected from damage under water and kept moist in land by a transparent nictitating membrane. Their keen vision helps them to detect moving insects.
They hear through tympanic membranes, or eardrums, which vibrate in response to sounds, sending sound waves deeper within the skull to the middle and inner ear.
Many also have lateral line systems to detect water movement.

9. Groups of Amphibians
The 3 groups of amphibians alive today are salamanders, frogs and toads, and caecilians.
Salamanders: Members of the order Urodela, have long bodies and tails, have 4 legs, are carnivorous, and usually live in moist woods.
Frogs and Toads: Members of the order Anura; frogs have long legs, make lengthy jumps, and live close to water, while toads have shorer legs, hop, and live in most forests or deserts; adults lack tails.
Caecilians: Members of the order Apoda, legless, live in water or burrow in moist soil or sediment, have scales.

11. Ecology of Amphibians
Amphibians must live near water, and are common in moist, warm places.
Amphibians who do live in deserts, such as some toads, stay inactive until heavy rain falls.
Markings and colors enable amphibians to blend in with their surroundings and avoid being eaten by predators.
Most amphibians have skin glands that contain poisonous substances/ toxins.