1. Chapter 25
Amphibians

2. Amphibian—a vertebrate that is well adapted to life both in the water and on land
Kingdom—Animalia
Phylum—Chordata
Subphylum—Vertebrate
Class—Amphibia
Orders—Anura, Urodela and Apoda

3. Life cycle
Mating
Males of some species croak loudly to attract a mate.
Eggs are fertilized externally
As many as 20,00 eggs may be laid at once, most do not survive
Tadpole
Emerge six days after eggs are fertilized
As they mature, internal gill are formed, legs emerge and the tail is absorbed.
Adult
Metamorphosis takes place when the tadpole releases a hormone call thyroxine
Only vertebrate to where life cycle includes metamorphosis
Develops adult teeth, a jaw and a shorter digestive tract, similar to most carnivores, a three chamber heart and replaces gills with lungs.
Process can take as few as eight days or up to three years.

4. Structures of frogs Legs
The legs of a frog are so strong they can jump over ten times their body length
Respiration
Breathes through lungs, but also must breathe through skin, cannot survive with lungs alone
Skin must stay moist to allow gases to pass through it, this is done with mucus glands.
Circulation
The frogs blood carries oxygen and nutrients to the body’s cells, while also removing carbon dioxide and waste.
Have a three chambered heart with a double loop circulatory system, as a tadpole, they have a single loop double chambered heart.
Digestion
Mouth, esophagus, stomach, small intestine then large intestine
Undigested food passes into a cloaca, common chamber and outlet into which the intestinal, urinary, and genital tracts open.

5. Diversity of Amphibians Anura
Frogs and Toads
Frogs have smooth moist skin, while toads have a dry rough skin
Frogs need to stay near water, toads only need water habitat for reproduction
Urodela
Salamanders
Long tail, long body and two pairs of legs
Smooth moist skin
5 cm small to 1.5 m longer
Brightly colored salamanders may be poisonous
Retain gills as adults

6. Look similar to earthworms, but have a skeleton
Apoda
Caecilians
Look similar to earthworms, but have a skeleton
Burrow through moist soil in search of insects and worms to eat, a few live in water
Average length is 30 cm
Internal fertilization, then female lays eggs.

7. Environmental Awareness
Ecological roles
Keep insect and other animal populations in check
The larval stage consume small plants and decaying animal matter.
Are a food source for other larger animals.
Human uses
Help control pest naturally
Food source, although not significant
Used in dissections to aid in knowledge of vertebrates
Poison from frogs used to coat arrows to aid in hunting
Environmental Awareness
Useful bio-indicator since there life cycle is very vulnerable.