Characteristics of Amphibian
Amphibians are ectothermic vertebrates, belonging to the class Amphibia and consist of
three orders: Urodela, containing the salamanders and newts; Manure, consisting of frogs
and toads; and Apoda, containing the caecilians. The larvae are typically aquatic and
breathe using gills. The adults are typically semiterrestrial and breathe both through moist
skin and by lungs.
For the purposes of reproduction, most amphibians are bound to fresh water. Although
there are no true seawater amphibians, a few tolerate brackish (slightly salty) water. Some
species do not need any water whatsoever, and several species have also adapted to arid and
semi-arid environments, but most still need water to lay their eggs.
In general, the life cycle of amphibians begins with a shell-less egg stage, usually laid the
previouswinterinapond. Alarvalstagefollowsinwhichtheorganismislegless, fullyaquatic
and breathes with exterior gills. After hatching, the larvae start to transform gradually
(metamorphosis) into the adult’s appearance, including loss of gills, growth of four legs, and
the ability to live in a terrestrial environment.
Adaptations for living in a terrestrial environment include replacement of gills with another
respiratory organ, such as lungs; a development of glandular (containing cells, a group of
cells, or an organ producing a secretion) skin to avoid dehydration, and the development of
eyelids and adaptation to vision outside the water. An eardrum also develops that separates
the external ear from the middle ear and, in frogs and toads, the tail disappears.
Salamanders
Thisisagroupofapproximately500speciesofamphibians, typicallycharacterizedbyslender
bodies, short legs, and long tails, and most closely related to the caecilians, little known
legless amphibians (Figure13.16). Having moist skin, salamanders (Figure13.15) rely on
habitats in or near water or under some protection on moist ground, often in a swamp. Some
species are aquatic throughout life, some are aquatic intermittently and some are entirely
terrestrial as adults.
Respiration varies among the different species of salamanders; in those that retain lungs,
respiration occurs through the gills as water passes over the gill slits. Some terrestrial species
have lungs that are used in respiration in a similar way as in mammals. Other terrestrial
salamanders lack both lungs and gills and exchange gases through their skin. This is known
asvalarian respiration,in which the capillary beds are spread throughout the epidermis.
Hunting prey is another unique aspect of salamanders. Muscles surrounding thehyoid
bonecontract to create pressure and “shoot” the hyoid bone out of the mouth along with
the tongue. The tip of the tongue has mucus which creates a sticky end to which the prey
is attached and captured. Muscles in the pelvic region are then used to bring the tongue
and hyoid back to their original positions. Another trait, unique among vertebrates, is the