Amphibia - Amphibians
Amphi - both, Bios - life, refers to the fact that they can live in or out of water

Kingdom - Animalia
    Phylum - Chordata
        Subphylum - Vertebrata
            Class - Amphibians

Basic Features:

Amphibia is a Class in the Subphylum Vertebrata of the Phylum Chordata, so they have all of the characteristics of both of these groups in addition to the following:

• Thin smooth permeable skin though which gas exchange (oxygen in, carbon dioxide out) can take place, gills are usually also present in the larvae and lungs in adults.
• Ectothermic, cold blooded.
• Soft unshelled eggs which must be laid in freshwater.
• Most members undergo a metamorphosis from larval (usually purely aquatic) to adult stage

Many Amphibia are highly toxic, the toxins being produced by poison glands on the skin. This toxicity often comes from the diet, taking on chemicals such as alkaloids from prey animals and synthesizing them into poisons.

Modern amphibians are experiencing declines in populations and extinctions, that have exceeded that of any other class over the last millennia. Of the 5,743 species of Amphibia, 32% are classed as at least threatened, compared to 12% of birds and 23% of mammals.

Population declines are associated with many factors, habitat loss through overexploitation of natural resources affects almost all threatened species, as well as the effects of climate change, and the fungal disease Chytridiomycosis (Batrachochytrium dendrobatidis) causing catastrophic levels of mortality.

---

What do amphibians eat?

Amphibians, for the most part are generalist carnivores. This means they will eat what they can get, what is abundant, and what they can fit in their mouths.  The majority of the time this includes invertebrates such as insects, worms, slugs etc, as well as smaller and larval stage amphibians.

Some bigger amphibians can feed on larger animals like birds, or mammals such as the giant salamanders which are capable of feeding on small mammals such as rodents.

---

What eats amphibians?

Lots of things. Amphibia play an important role in food webs, and many species of bird, mammal, reptile and larger amphibians rely on them as an energy source. The conservation of amphibians is of great importance, not only for their own sakes, but for trophically higher organisms and the whole ecosystem.

---

The group includes:

The names of Amphibian groups should be taken as a work in progress, as they are revised; changed; and revised again.

Anura: Frogs and toads.
An = Without   Uro = Tail

Four legged, generally have large hind limbs for jumping (saltatorial), swimming (natatorial), climbing, hopping or burrowing.

The largest Amphibian order, the Anura make up 88% of all Amphibians, containing more than 6100 species, found all over the globe except Antarctica.

Eggs are generally termed as a 'spawn' when laid in a gelatinous grouping, and laid in water, producing aquatic larvae called tadpoles. Some species however can develop directly on land, those of the genus Nectophrynoides and Nimbaphrynoides give birth to live young rather than eggs, a process known as viviparous spawning.

Ranidae - These are the 'true frogs' and what you are most likely to imagine when thinking of a frog. A family of 371 species, showing a general frog body plan and aquatic larval stage. Common frog -Rana temporaria.

Bufonidae - These are the diverse 'true toads' of which there are 577 species. They have shortened forelimbs (strong and used for mate retention in males during mating), dry, warty / bumpy skin and eggs are laid (generally) in strings as opposed to clumps like many frogs.

Cane toad - Bufo marinus (Introduced in Australia to limit rodent and beetle pests but now a massive problem as it has very toxic skin secretions which makes it immune to most predators.

Desert toad - Bufo alvarius  Burrows underground in arid areas, only surfacing to feed. Takes up water from the ground through a patch in the  pelvic region.

Hylidae - the 'Tree frogs', one of the largest families in the order Anura , with 911 species. They are spread across the globe, and found especially in forests, hence the name, most are small. Hyalids can be identified by their adhesive toe discs.

Dendrobatidae -The poison dart frogs, 283 species of small bodied, highly aposematic (having warning colours) individuals found in the neo tropics. Many species are also highly toxic, deriving their toxins through eating their prey, producing alkaloid chemicals secreted on their skin.

Urodela / Caudata
Uro = tail   Delos = evident

Over 500 species making up approximately 9% of all Amphibia, legged and non-legged forms.

Dicamptodontidae - Medium to large salamanders (30cm+). Many members can be aggressive, bearing well developed teeth used to capture mammalian prey. Contain some of the few examples of species that can vocalize.
Giant Californian salamander - Dicamptodon ensatus (can 'bark').

Salamandridae - The' True salamanders' and newts. Small to medium sized, terrestrial and aquatic adult stages. Many show impressive secondary sexual characteristics such as crests.
Great crested newt - Triturus cristatus, Fire salamander -Salamandra salamandra, Spanish newt - Pleurodeles watl (rib popping).

Cryptobranchidae - Generally large animals, includes the largest amphibian, at 1.5m the Chinese Giant Salamander Andrias davidianus. Dorsoventrally flattened, fully aquatic salamanders. Sometimes referred to as Hellbenders in the USA.

Proteidae -Medium sized, fully aquatic neotenic family containing 6 species. Often termed 'mudpuppies' or 'waterdogs', elongate with external filamentous gills, resembling a longer, more slender axolotl. Neuse river waterdog -Necturus lewisi.

Amphiumidae - 3 species, all large (1m+) and elongate with very reduced hind and forelimbs, often resembling an eel. Completely aquatic, though using lungs to breathe air as an adult, losing the juvenile gills.
3 toed amphiuma -Amphiuma tridactylum.

Plethodontidae -The largest family in Urodela, 370+ species. Characterised by the nasolabial groove for olfaction (smelling). Most species are completely terrestrial (including juveniles) and lungless , breathing through the skin.

Gymnophiona: Gymno = naked 

The Caecilians, with 3% of all Amphibian species. Being elongate, legless, and with a segmented look from skin folds, they are often compared to worms or eels.

All species require moist conditions. The name Caecelian is derived from the Latin 'Caecus' meaning blind, with most species living underground, eyes are rudimentary and scarcely function or completely gone, with a strong skull and head muscles for burrowing. Sensory information is picked up through chemo and tactile sensory organs in tentacular openings in the head. Fertilization is internal, with viviparity (live birth) and oviparity (egg laying) exhibited by various species.

Caecilidae - 42 species from 10cm -1m+, eyes are surrounded, or covered by the skull. They are found in South and Central America , often in disturbed ground such as farmland.

Ichthyophiidae - 51 specie,s a 'true tail' with vertebrae and dual closing jaw for predation. They are dispersed around Asia.

Typhlonectidae - 13 secondarily aquatic species (amphibians began as aquatic, then the Caecelians became terrestrial, this group then returned to the water again) viviparous species that all burrow, under or near water bodies. Semi or fully aquatic with  lungs for gas exchange.