The Class Amphibia
The Amphibia are characterized by having moist, glandular skin that lacks the keratinized scales of reptiles. Most amphibians have complex life cycles (adults, eggs, and larvae that metamorphose into juveniles). Amphibians lay eggs that are non-amniotic (they lack the amniotic membrane that surrounds the embryo). Amphibian eggs don't have a shell, instead they are surrounded by several gelatinous layers. Most amphibian larvae have gills and most adults have lungs. In many amphibians, the skin is also important in gas exchange. The class Amphibia includes the orders Gymnophiona (caecilians), Urodela (newts and salamanders) and Anura (frogs and toads). Of these three, only the last two are represented here in Idaho. The caecilians (Gymnophiona) are limbless amphibians found mostly in the tropics.
(Salamanders and Newts)
Amphibians in this order are characterized by having a true tail. In fact the name "Urodela" translates as "visible tail." Adult characteristics are the lack of a tympanum (external ear drum), and legs that are adapted to walking rather than jumping or hopping. Generalized larval characteristics of the order are that they have teeth, are carnivorous, and have limbs during most of their development.
(Frogs and Toads)
The order Anura is comprised of the frogs and toads. The most readily distinguishable characteristic of this order is the absence of a tail in the adult form. In fact the name Anura is translated as "without a tail." Even species that appear to have a tail don't really have one. For example, Idaho has a species named the Tailed Frog. However, this is not a true tail; rather it is the everted cloaca. The caudal vertebrae of anurans are fused into a rod called the urostyle (Pough, 1998). Adult anurans lack an outwardly apparent neck. And finally, their hind limbs are longer than their front limbs, being modified for hopping, jumping or swimming.
The larvae of anurans are called tadpoles. Tadpoles in general, lack true teeth, are usually herbivorous, and develop hind limbs before front limbs (which is the opposite of Urodela larvae). Anuran larvae also lack external gills, having opercular chambers that allow water to flow over internal gills, before exiting through a spiracle.