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Amphibians
What is an Amphibian?
The word amphibian means
“double life”, because these
animals live both on water and on
land during their life.
They are vertebrates that live in
water as larva and on land as
adults. The adult form breathes
with lungs, has moist skin and do
not have scales and claws.
Form and Function in Amphibians
In frogs, tadpoles are filter feeders or
herbivores that eat algae. The tadpoles will
eat constantly.
As a tadpole becomes an adult it will only
eat meat. They eat anything they can catch
and swallow.
In their digestive system they have a
mouth, stomach, small intestines (where
food is absorbed), tubes to connect the
liver, pancreas, and gallbladder to the
intestine to help in digestion, and then the
small intestine leads to the large intestine.
At the end of the large intestine is the
cloaca where digestive waste, urine, eggs
or sperm exit the body.
Respiration
For larval amphibians, gas exchange
takes place through the skin and
gills. Lungs will replace gills in
adults, but gas exchange still also
takes place through the skin.
Many salamanders do not have
lungs, so all of their gas exchange
takes place through their skin.
Circulation
They have a double loop system. The
first loop takes oxygen-poor blood
from the heart to the lungs and skin,
then takes the oxygen-rich blood back
to the heart. The second loop takes
oxygen-rich blood from the heart to
the rest of the body and brings
oxygen-poor blood from the body back
to the heart.
The heart has 3 separate chambers:
left atrium, right atrium, and ventricle.
There is some mixing of oxygen-poor
and oxygen-rich blood in a three
chambered heart.
Excretion
Amphibians have kidneys that filter
waste from blood.
Reproduction
Amphibians eggs must be kept
moist, so many amphibians lay eggs
in the water. Fertilization is
external.
Metamorphosis takes place after
the egg hatches. The egg forms a
tadpole that can only live in water.
The tadpole will grow limbs, lose
their tail and gills. Eventually they
will become a land dwelling adult.
Movement
Adult amphibians use their front
and back legs to move. Frogs and
toads can jump long distances.
Some amphibians have suction
cups on their toes for climbing.
Response
Amphibians have well developed
nervous and sensory systems.
Amphibians have large eyes that are
protected from damage under water
and kept moist by a clear nictitating
membrane – this is movable and
located inside the regular eyelid.
Amphibians have good eyesight so
they can see and respond to moving
insects. They cannot see in color.
Amphibians hear with a tympanic
membrane (eardrums).
Groups of Amphibians
There are 3 main groups:
salamanders, frogs and toads, and
caecilians.
Salamanders
This is the order Urodela – includes
salamanders and newts. They have
long bodies and tails. Most have 4
legs. Both adults and larvae
carnivores. Adults will be found in
moist woods under rocks and
rotting logs.
Some salamanders have gills and
live in water all of their life.
Frogs and Toads
This is the order Anura. They all can
jump. Frogs have long legs, but
toads have short legs and can only
make small hops.
Frogs need to be close to water
their whole life. Toads can live in
moist woods and even desserts.
Caecilians
Order Apoda. These are legless
amphibians that will live in water or
burrow in moist soil. They eat small
invertebrates like termites.
Importance of Amphibians
Most amphibians must live in wet
environments. Very few live in
desert areas .
Many birds and mammals eat
amphibians. But to protect
themselves many are camouflaged.
Many toads are unpleasant tasting
or produce poisons.
For some reason amphibian
populations have been declining. It
is not known really why.