Amphibians 2

8/19/2019 Amphibians 2

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Amphibians

Copyright Cmassengale


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Evolution ofAmphibians


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"Amphibian" comes from theGreek meaning "both life".

Amphibians can live on waterand on land.

Scientist infer that

amphibians evolved fromlobe-finned fishes calledcrossopterygians.


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Crossopterygian


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Biologist conclude that amphibians appearedduring the late Devonian period, about 345

million years ago.


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Crossopterygians had no gills but they hadinternal nostrils and a primitive lung that

may have enabled them then to respire forperiods of time on land.


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Characteristics

of Amphibians


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Amphibians are coldblooded, !hich

means their blood temperature risesand falls !ith that of the surroundingenvironment

•


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"hey use gills, lungs, s#in, and mouth

cavity in respiration.


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"hey have moist, smooth, thin s#in !ith noscales.$eet are !ebbed and the toes lac# cla!s.


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Amphibians have many prominent characteristics that areadaptations to a life spent both on land and in !ater%

"hey change from an a&uatic larval stage to a terrestrialadultform. "his transformation is called metamorphosis


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Amphibians enter a state ofdormancy or torpor when

conditions are unfavorable.They often bury themselves inmud or leaves, emerging whenconditions are better.


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'uch states of inactivityare #no!n as #no!n as%

ibernation when it occursin the winter

!stivation when it occursin the summer


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Larvae have two-chamberedhearts; adults have three-

chambered hearts and well-developed circulation.


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Eggs lack multicellular membranes or

shells. They are usually laid in water orin a moist environment and fertilizedeternally.


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Classification ofAmphibians


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Biologists have identified about (,3)5living species of amphibians and haveclassified them into four orders

Anura #rogs $ Toads

%rodela Salamanders

Trachystoma &ud eels Apoda - 'aecillians


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$rogs and toads ma#e up the

*rder Anura +!ithout atail-.


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'alamanders and other amphibians!ith legs and tails ma#e up the*rder rodela +visible tail-.


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.Some a(uatic amphibians )mud eels

$ sirens* belong to the +rderTrachystoma )"rough mouth"*


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'iren


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Apoda includes caecilians, atropical, burro!ing !ormli#e

amphibians that is often

/egless


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AnuranCharacteristics


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$rogs and toads comprise the

order Anura

"here are about 3,500 #no!n

species of frogs and 300 #indsof toads

"hey are found on everycontinent e1cept Antarctica


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'ome types spend their entire life inor near !ater, but others live mainly

on land and come to the !ater only tomate


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'ome frogs and toads are climbers

that d!ell in trees or burro!ers thatlive underground.


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"oads and frogs have manysimilarities in the !ay they loo#. 'omebasic differences bet!een them are%

toads have dry, !arty s#in, !hilefrogs have smooth, !et s#in.


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Both frogs and toads return to !ater to

reproduce. 2n nearly all species eggs arefertilied e1ternally. "he fertilied eggshatch into s!imming larval forms called

tadpoles


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rodelanCharacteristics


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'alamanders, typical members of the*rder rodela, have elongated

bodies, long tails, and smooth, moists#in


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Compared to the anurans, salamanders are

less able to remain on dry land, althoughsome can live in dry areas by remaininginactive during the day


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'alamander lay their eggs in!ater and li#e anurans theyhatch into s!imming larva

!alamander eggs


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*ther species can reproduce indamp land environments. Eggs laidon land hatch into miniature adult

salamanders

&arbled Salamander


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ApodanCharacteristics


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Caecilians, members of the *rderApoda, compose a highly specialied

group of tropical burro!ingamphibians


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These legless wormlike creatures average cmlong, but they can be up to .m long.

They have very small eyes and are often blind.

They eat worms and other invertebrates


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"he caecilian male deposits spermdirectly into the female, and the

female bears live young


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"rachystomaCharacteristics


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The +rder Trachystoma containsthree living species of mud eels,or sirens.

Sirens live in the eastern %nited

States and northeastern &e/ico.


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$rog E1ternalAnatomy


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The frog0s powerful hind legs are e(uallyeffective in 1umping or swimming. +n land frogssit with their hind legs folded against the body,poised to 1ump at the first sign of danger.

&ost frogs can make leapsmany times their body

length


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$rogs eyes also !or# e&ually !ell in or out

of !ater. Because the eyes bulge out fromthe head, the frog can stay submerged!hile literally #eeping an eye out for

predators


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!yelids that can blink protect the frog0s eyes from dust

and dehydration

In addition to upper and lower eyelids, a third,

transparent eyelid called a nictitating membranecovers each eyeball and joins the lower eyelid

This membrane keeps the eyelid moist and protects it when

it is under water


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$rogs have eardrums, or tympanicmembranes, !hich are circularstructures located behind each

eye

Tympanic membrane


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The frog0s thick, moist skin

serves two important functions2respiration and protectionGlands secrete mucus to keep itfrom drying up


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'ome glands secrete foultasting or

poisonous substances that protect thefrog from enemies


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'ome frogs, such as 5ylaversicolor, can change color inorder to blend !ith the

environment.'ount thenumber of

frogs in thepicture3


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$rog 2nternal

Anatomy


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'#eletal 'ystem

The frog0s spine has ninevertebrae

The cervical vertebra at theanterior end of the spine allowsneck movement that helps frogscatch prey


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'#eletal 'ystem

4osterior to thisare seven trunkvertebrae, and

then a single sacralvertebra thatsupports the hindlegs

A long, slim bonecalled the urostylee/tends from thesacral vertebra


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'#eletal 'ystem

5ones of the pectoralgirdle, which form theshoulders, connect to

the front legs They also provide the

primary protection tothe internal organs,

since the frog has noribs The pelvic girdle

connects to the hindlegs


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Digestive 'ystem


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Digestive 'ystem

&ost frogs feed on insects, and theirdigestive system is adapted to their diet

A frog0s tongue is an e/cellent insectcatcher. The frog simply flicks out itslong sticky tongue, curls it around itsprey, and pulls the insect back into itsmouth. Then the frog snaps its mouthshut and swallows.


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Digestive 'ystem#rogs have twotypes of teeththat hold on toprey. A row of

ma/illary teethline the perimeterof the upper 1aw.Two patches ofvomerine teeth

pro1ect frombones in the roofof the mouth.


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Digestive 'ystem

Sometimes the frogblinks, pulls its eyesinward, and presses themagainst the roof of its

mouth. This action helpspush the food down itsthroat

6igestion in frogs takesplace in the alimentary

canal, which includes theesophagus, stomach, smallintestine, large intestine,and cloaca

l


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Circulatory 'ystem An adaptation to the

greater o/ygen needs ofland animals is a moreefficient circulatory systemthan the fish0s two-

chambered heart. The amphibian0s three-chambered heart partiallymi/es o/ygenated withdeo/ygenated blood and

pumps the blood throughoutthe body at higherpressure than does thefish0s heart


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The left atriumreceives o/ygenatedblood from the lungs,and the right atriumreceives deo/ygenatedblood from the body.

5oth the atria emptyinto the ventricle, the

main pumping chamberof the heart. 7n the ventricle

o/ygenated anddeo/ygenated blood mi/

partially and arepumped to the lungs andthe rest of the body.

5lood to

body

6eo/ygenated

blood

from body

R

+/ygenatedblood from

lungs


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From the rightatrium the bloodenters the single

ventricle. Theventricle thencontracts, pumpingsome blood to thelungs to receiveoxygen and some tothe rest of the body.

The blood going tothe body leaves theventricle through the

conus arteriosus, alarge vessel that liesagainst the frontside of the heart


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This vessel divides into a right and a left truncusarteriosus, which immediately branch again into threearches that carry blood to various parts of the body.

6eo/ygenated blood travels in veins back to the rightatrium from the various regions of the body.

+/ygenated blood returns from the lungs to the leftatrium via the pulmonary veins


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6espiratory

'ystemTadpoles respire, or

e/change carbon dio/ideand o/ygen, throughgills


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6espiratory

'ystemAdult frogs lose the gills butcan respire in three ways8through the lungs, through the

skin, and through the mouth.9espiration through the lungsis called pulmonary respiration.

A frog breathes by changing

the volume and pressure of airin its mouth while eitheropening or closing its nostrils

6 i t ' t


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6espiratory 'ystem

Air moves from the throat to the lungsthrough a slit-like passage called theglottis.

5ecause the frog0s lungs are small,cutaneous respiration, or respiration

through the skin in both air and water,is very important, especially duringestivation or hibernation.

+/ygen can diffuse across the lining ofthe mouth and into the blood.

#rogs use mouth breathing for only arelatively small amount of theirrespiration.


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E1cretory 'ystem %rine and wastes from the digestive system are eliminated

through the anus.

:hen a frog is in water, its permeable skin allows the water toenter its body.

#rogs that live primarily in water rid themselves of e/cesswater by e/creting a large volume of very dilute urine.

#rogs that live mainly on land conserve water by producing asmall volume of more concentrated urine.


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E1cretory 'ystem Amphibians eliminate two primary types of metabolic

waste products2carbon dio/ide from respiration andwaste compounds from the breakdown of foods.

Are the primary e/cretory organs and lie on either

side of the spine against the dorsal body wall. Thekidneys filter nitrogenous wastes from the blood

"h 7 ' t


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"he 7ervous 'ystem

The frog brain is morecomple/ than the fish brain,enabling the frog to contendwith a more varied

environment. The optic lobes, which control

vision, lie behind thecerebrum.

The cerebellum, a small bandof tissue lying at right anglesto the long a/is of the brain,is the center of balance andcoordination.

7 ' t


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7ervous 'ystem

The medulla oblongata lies at the backof the brain and 1oins the spinal cord.7t controls organ functions.

Ten pairs of cranial nerves e/tend outdirectly from the brain. The spinal cord transmits signals from

all parts of the body to the brain andfrom the brain back to the body.

The spinal nerves branch from thespinal cord to various parts of thebody.

6 d ti ' t


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6eproductive 'ystem

5oth male and female frogs haveinternal se/ organs

The male frog0s foreleg musclesand first fingers swell

These swellings help the malemaintain his grasp on the female The reproductive system of the

male frog includes two bean-shapedcreamy white or yellowish testeslocated near the kidneys

Sperm cells develop in the testesand pass through tubes to thekidneys and urinary ducts &ale System

6 d ti ' t


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6eproductive 'ystem #emale frogs a pair of large,

lobed ovaries containing thousands of tiny immature eggslie near the kidneys

6uring the breeding seasoneggs enlarge, mature, andburst through the thinovarian walls into the bodycavity.

They remain in structurescalled ovisacs until ovulationis complete and then leave

the body through thecloacae opening.

#emale System

6 d ti ' t


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6eproductive 'ystem

The vast ma1ority of eggsand tadpoles are eaten bypredators such as fish,

birds, snakes, and turtles.Some species of frogshave

The vast ma1ority of eggsand tadpoles are eaten bypredators such as fish,birds, snakes, and turtles. Ample/us

8 t h sis

http://www.student.loretto.org/zoology/imgres


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8etamorphosis

;ewly hatched tadpoles live off yolk stored in theirbodies. They gradually grow larger and develop threepairs of gills.

Tadpoles have a two-chambered heart. Tadpoles can also

regenerate in1ured or lost body parts such as a leg ortail.


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8etamorphosis

The mouth broadens, developingteeth and 1aws. A saclike bladderin the throat divides into two sacsthat become lungs. The heart

develops a third chamber. A hormone called thyro/in

circulates throughout thebloodstream and stimulatesmetamorphosis.

The cells of the tadpole aregenetically programmed to respondto thyro/in at the appropriatestage of development.

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Amphibians 2

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