CLASS: Amphibia
("amphi" both,
"bio" lives, in reference to the
tadpole/frog life stages;
from Greek.)
Frogs,
toads, salamanders,
newts & caecilians
Definition:
Animals that lack internal gills as adults, generally form at least
rudimentary limbs as adults, undergo metamorphosis from an
external-gilled larval stage to adult, have reduced cranial
ossification, a three-chambered heart, and a gland-rich moist skin.
Amphibia have two occipital condyles, unique green rods in the eyes,
and ten pair of cranial nerves.
Though extremely numerous during the Carboniferous in terms of
taxa and numbers, living amphibians are now limited to a mere three
orders. They were the first truly terrestrial vertebrates, and
possibly the first vertebrates with true voices. Today, frogs and
toads still use their voices, but other amphibians are generally mute.
Living amphibians are extremely sensitive to their environments,
and generally need to live where their skin can stay moist. Desert
dwelling species are active at night or for brief periods after rains.
Only a very few frogs and toads can tolerate salt water, and these for
only very brief encounters. Thus, amphibians are absent from beaches
and saltwater bodies, though many species inhabit marshes that abut
bays and estuaries.
Though it was long held that amphibians have to return to water to
breed, it has since been discovered that nearly half known species lay
eggs on land, a very few laying eggs with a shell-like parchment.
Other species brood eggs or young in throat pouches, dorsal pouches,
or even the stomach. At least one species of caecilian is known to
feed its young with a milky dermal secretion. Obviously, amphibian
reproduction
is a varied and a fruitful area of study.
References:
click on book to order.
Duellman,
Wm., and Linda Trueb. 1986. Biology of amphibians. McGraw-Hill.
Hofricher,
Robert (editor). 2000. Amphibians: the world of frogs, toads,
salamanders and newts. Firefly Books.
Links:
Amphibian Species of the World Checklist:
www.research.amnh.org/herpetology/index.html/
