Chapter 25 Amphibians

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

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.

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.

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

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.

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.