Amphibians are a group of cold-blooded vertebrate animals that belong to the class Amphibia. They are characterized by features such as a metamorphic life cycle, moist and permeable skin, and typically a dual life both in water (during their larval stage) and on land (as adults).
Amphibians include animals like frogs, toads, salamanders, and caecilians. They are known for their ability to breathe through their skin, their ectothermic nature (relying on external heat sources for temperature regulation), and their crucial roles in various ecosystems, particularly in freshwater environments.
What are Amphibians?
Cold-blooded vertebrate animals that belong to the class Amphibia. They are characterized by several key features that distinguish them from other animal groups.
Characteristics of Amphibians
Life Stages
Amphibians typically go through a metamorphic life cycle with two main stages: larval and adult. The larval stage usually occurs in water, where amphibians hatch from eggs and resemble aquatic tadpoles. As they grow, they undergo metamorphosis, developing into their adult form, which can be aquatic, terrestrial, or both.
Moist Skin
Amphibians have thin, moist, permeable skin that allows them to exchange gases (such as oxygen and carbon dioxide) and water directly with their environment. This feature is crucial for respiration, especially in the larval stage.
Ectothermy (Cold-Blooded)
Like reptiles, amphibians are ectothermic, meaning their body temperature is regulated by the external environment. They cannot generate internal heat and must rely on external sources for warmth.
Legs (in Adults)
Adult amphibians typically have four legs, although some legless species exist. These legs are adapted for terrestrial locomotion and vary in structure depending on the species.
Lungs and Cutaneous Respiration
Adult amphibians have lungs, but many species also rely on cutaneous respiration (breathing through their skin) to supplement their oxygen intake, especially in moist environments.
Double Circulation
Amphibians have a three-chambered heart (two atria and one ventricle), which results in somewhat mixed oxygenated and deoxygenated blood but is more efficient than the hearts of fish.
External Fertilization
Many amphibians practice external fertilization, where eggs are fertilized by sperm outside the female’s body, often in water bodies.
General Features
Metamorphic Life Cycle
Amphibians typically undergo a metamorphic life cycle, transitioning through distinct larval and adult stages. The larval stage often takes place in water and is aquatic, while the adult stage can be terrestrial, aquatic, or semi-aquatic.
Moist and Permeable Skin
Amphibians have thin, moist, and permeable skin that allows them to exchange gases (such as oxygen and carbon dioxide) and water directly with their surroundings. This characteristic is crucial for respiration and thermoregulation.
Legs (in Adults)
Adult amphibians typically possess four legs, although some species have adapted to legless or reduced-limb forms. These limbs are adapted for terrestrial locomotion.
Lungs and Cutaneous Respiration
While adult amphibians have lungs, many species rely on cutaneous respiration, or breathing through their skin, as an essential supplement to their oxygen intake, particularly in moist environments.
External Fertilization
Many amphibians practice external fertilization, where eggs are fertilized by sperm outside the female’s body, often in water bodies.
Double Circulation
Amphibians have a circulatory system with two circulatory circuits: a pulmonary circuit that takes blood to the lungs and a systemic circuit that distributes oxygenated blood to the body.
Habitat Diversity
Amphibians inhabit a wide range of habitats, including freshwater ecosystems, forests, grasslands, and wetlands. Some species are highly specialized for certain environments, while others are more adaptable.
Vocalizations
Many amphibians, especially frogs and toads, are known for their vocalizations used in communication and mating rituals.
Types of Amphibians
Anurans (Order Anura)
Anurans are the most diverse and well-known group of amphibians. They include frogs and toads. Anurans are characterized by their typically smooth, moist skin, long hind legs adapted for jumping, and the absence of a tail in adults. They are found in a wide range of habitats worldwide, from forests and wetlands to deserts.
Urodeles (Order Caudata)
Urodeles, also known as salamanders or newts, are characterized by their elongated bodies, long tails, and relatively short legs. Unlike anurans, they have moist skin and a distinct tail in both larval and adult stages. Many urodeles are terrestrial, but some are fully aquatic or semi-aquatic.
Gymnophionans (Order Gymnophiona)
Gymnophionans are commonly known as caecilians. They are often the least familiar group of amphibians to people because they are mostly burrowing and legless. Caecilians have elongated, cylindrical bodies and are found in tropical regions, primarily in the soil and leaf litter of forests and other moist environments.
List of Amphibians
- African Bullfrog
- African Clawed Frog
- African Tree Toad
- American Toad
- Argentine Horned Frog
- Bullfrog
- Burrowing Frog
- Caecilian
- Common Frog
- Darwin’s Frog
- Desert Rain Frog
- Edible Frog
- Fire Salamander
- Fire-Bellied Toad
- Frog
- Giant Salamander
- Glass Frog
- Goliath Frog
- Gray Tree Frog
- Green Frog
- Green Tree Frog
- Holy Cross Frog
- Leopard Frog
- Mantella Frog
- Marine Toad
- Marsh Frog
- Monte Iberia Eleuth
- Mudpuppy
- Natterjack
- Newt
- Oak Toad
- Olm
- Oregon Spotted Frog
- Poison Dart Frog
- Pool Frog
- Red-Eyed Tree Frog
- Salamander
- Scrotum Frog
- Sehuencas Water Frog
- Spadefoot Toad
- Striped Rocket Frog
- Tiger Salamander
- Tree Frog
- Turtle Frog
- Wood Frog
- Wyoming Toad
Amphibians FAQS
What are amphibians?
Amphibians are a group of vertebrate animals known for their unique life cycle, typically featuring an aquatic larval stage and a terrestrial or semi-aquatic adult stage.
How do amphibians breathe?
Amphibians have moist and permeable skin that allows them to exchange gases (oxygen and carbon dioxide) directly with their environment.
Why are amphibians sensitive to environmental changes?
Amphibians are highly sensitive to environmental changes, including pollution, habitat destruction, and climate change, because of their permeable skin and complex life cycle.
Are amphibians cold-blooded or warm-blooded?
Amphibians are cold-blooded, which means they are ectothermic and rely on external heat sources to regulate their body temperature. Their body temperature fluctuates with their surroundings.
What is the largest amphibian in the world?
The Chinese giant salamander (Andrias davidianus) holds the title for the largest amphibian, with some individuals reaching lengths of up to 5.9 feet (1.8 meters).
Do all amphibians have legs?
No, not all amphibians have legs. While most amphibians have four limbs, some, like caecilians, are legless.