Most people think about amphibians (if they think about them at all) as cold, slimy, and not very bright. However, when amphibians were the most exciting animals on land. They were, in fact, the only animals on land except for some arthropods and an occasional lobe-fined fish.
Representatives of the three major extant groups of amphibians:
Caecilians (order Gymnophiona), such as this yellow-striped caecilian Ichtyophis katouensis, are rarely seen because they are wormlike burrowing animals of the tropics. Caecilians are legless, withe skeletons resembling those of snakes. Like snakes, but unlike other amphibians, some species have dermal scales as protection against abrasion. As in snakes, the lungs are long and thin, and the left one is often much smaller than the right. Some 160 species occur in tropical forests of Central and South America, Africa, India, and the Seychelles islands in the Indian Ocean.
Ordo that still exists today is:
Ordo Gymnophiona or Apoda, and other orders are extinct.
the example is :
picture1.
Ichtyophis katouensis
Salamanders (order Caudata = Urodela) have legs adapted for walking and a tail. Most remain in or close to water, but the adult Eastern newt
Notophthalmus viridescens, known as the red eft, spends several years wandering over land. Salamanders most resemble the earliest amphibians, with long post-anal tails, and legs of approximatelly equal size suitable for walking. The larvae of urodeles are generally aquatic, with pharyngeal gill slits, external gills, and broad tails that serve as caudal fins for swimming.
This sub-class consist of 3 ordo, there are:
Ordo Proteida, the example is:
picture 2a.
Necturus lewisi
picture 2b.
Notophthalmus viridescens
Ordo Mutabilia
, the example is:
picture 2c.
Plethotn tidae
Ordo Meanthis, the example is
Psandobranchus striatus
Frogs (order Anura) the most of amphibians. Because of their enlarged hind legs, frogs walk poorly but can hop and swim well. The bullfrog
Rana catesbiana is one of the largest and most common frogs of North America. It spends much of its time resting in water with its green head camouflaged among algae and vegetation. The nostrils and upper halves of the eyes are usually above water, while
the lower halves of the eyes watch beneath the surface of the water. Adults frogs range from 1 to 30 cm long and feed mainly on insects and other invertebrates
picture 3a.
Rana catesbiana
picture 3b.
Bufo americanus
The Generall characteristic of amphibians:
- Unlike other lizards, tails of salamanders lack fracture zones. they have the ability to regenerate their limbs.
- Though female toads hardly make noise, male toads are known to be one of the noisiest amphibians.
- Most amphibians are good bio-indicators (organisms that tell
something about the area they live in), as they are adapt to conditions
in water as well as on land.
- Amphibians possess a three-chambered heart and most species have two
lungs (except in some that have no lungs or possess reduced lungs).
- Frogs
differ from toads in their habitat and skin texture. Most of their
lifetime, frogs live in water and have smooth skin; whereas, toads live
mostly on land and possess rough skin.
- A frog in a dormant state requires
very little oxygen for breathing, which is achieved through cutaneous
gas exchange (breathing via skin).
SKIN
The skin of amphibians sacrifices protection from abrasion and and dehydration to provide a means of exchanging O
2
and CO
2 , especially in an adult frog totally immersed in
water. Even on land the skin absorbs almost as much O2 as the lungs
do, and it eliminates most of the CO2. The respiratory function of
the skin depends to a large extent on its thinnes. The epidermis is only
a few micrometers thick, permitting easy diffusion of gases to and from the
blood capillaries in the underlying dermis. There is an outer layer cornified
layer containing the protein keratin, it is generally too thin to provide
more than taken protection.
picture 4a. skin of frog
Defense.
Frog skin is unique in that it is attached to underlying tissues in only a few
places. The loose attachment of the skin probably helps frogs escape from
predators, especially smaller birds and other animals that cannot swallow a
frog whole. Slippery secretion from mucous glands in the dermis probably also
helps frogs slip away from predators. The another function is to keep the skin
moist so that it remains permeable to respiratory gases. The skin of amphibians
also contain poison glands that often concentrated in thickenings of the skin
or in bulges behind the eyes called parotoid glands.
Colors. Many
toxic amphibians are brightly colored, and potential predators soon learn to
avoid them. Red, orange, yellow warning colors are due to pigmens in certain
chromatophores, and blue is a structural color reflected from other kinds of
chromotophores. These chromatophores, called melanophores or melanocytes, are
also partly responsible for the darkening of the skin which often occurs when
amphibians are on a dark substratum or in darkness. Control of the melanocytes
is partly due to melanocytes stimulating hormone (MSH) from the pituitary.
picture 4b. the poisonous frogs
INTERNAL
ORGANIZATION
Lungs. The
lungs often account for more than half the oxygen taken into the blood when a
frog is on land, and virtually all the oxygen when it is floating in stagnant
water with only the eyes and nostrils above the surface. Small amounts of
respiratory gases are also exchanged across the lining of the buccal cavity.
picture 5a. The location of lung
picture 5b. the lung of frog
Circulation.
The amphibians heart has a second atrium that allowa deoxygenated blood from
the body tissues to be separated from oxygenated blood coming from the lungs
and skin. Deoxygenated blood enters a chamber called the sinus venosus on the
back of the heart, which pumps the blood into the right atrium. At the same
time oxygenated blood from the skin and lungs enters the left atrium. In some
salamanders and frogs, such as Xenopus laevis, the deoxygenated and
oxygenated blood mix in the ventricle.
picture 6. heart of frog
Osmoregulation
and Excretion. The kidneys compensate for the loss or gain of water through the
skin. The kidneys are the mesonephric type. The urines passes from the kidneys
through the ureters into the cloaca and may then be excreted immediately or
stored in bladder.
picture 7. internal organization of frog
picture 3. Bufo melanostictus, Kodok Puru, bangkong kolong, Black-spined Toad, Yogyakarta
