Frogs

Class Amphibia

  Amphibia is derived from Greek words which mean "on both sides of life".  Part of their life is spent in water and part is spent on land "Double Life".

Includes:  frogs, toads, salamanders, & caecilians (se sil i anz)

size range:  tiny frog of Cuba 1/2 inch in length to giant salamander over 5 feet

none are marine

They are ectothermic (cold blooded) - not able to maintain a constant body temperature; body temp. varies with the temp. of the environment

  Classification:

     3 orders based on body shape and type of limbs:

     1.  Order Apoda (AP uh duh) - Greek word meaning "without feet"

                     contains caecilians (comes from Latin word meaning "blind"

                     strictly underground creatures - totally

                     blind as adults

                     wormlike - lack limbs

     2.  Order Caudata (kaw DAH tuh) - from Latin "having a tail"

                     contains:  salamanders, newts, and sirens

                     often mistaken for lizards

                     largest living amphibian - Japanese giant salamander (5 ft.)

     3.  Order Anura (uh NOOR uh) - Greek meaning "without tail"

                     contains:  frogs and toads

         3 groups of anurans:  (Genus)

         A.  Rana - frogs

                       remain near water

                    smooth, shiny skin that dries easily

         B.  Bufo - toads

                    strictly land dwellers (enter water only to mate)

                    rough, dry, warty skin

         C.  Hyla - tree frogs

                    usually smaller than frogs and toads and have enlarged, sticky discs at the end of each toe

         

 

leopard frog
(Rana pipiens)

  Movement: three types of muscle

 

Body Covering:

     skin

          3 functions of amphibians' skin:

          1.  body covering

          2.  protection

              a.  secretes poisonous substances

                  may just taste bad

                  may be strong enough to burn

                  may be fatal

                  Arrow poison frog

                    (To be effective, the toxin must enter the bloodstream directly; digestive enzymes destroy the toxin, making it safe to consume poisoned game.)

              b.  camouflage

                    chromatophores

          3.  respiration

 

Support:

     endoskeleton

 

Nutrition:

     Flips out its long sticky tongue & snatches prey.

     Then it flips the tongue and insect into its mouth.

     teeth:  2 sets in upper jaw

             maxillary (MAK suh lehr ee)

             vomerine (VO mur in)

             teeth are not used to chew or bite food

             function - helps to hold prey

     To swallow:  uses blinking eyes to help force food down the gullet

     path of food:

          esophagus

          stomach (pyloric valve)

          small intestine (duodenum to ileum)

          colon (large intestine)

          cloaca (klo AY kuh) - the cavity which collects and stores wastes from both the colon and kidneys

          anus

     two glands which are part of the frog's digestive system:

          liver - largest organ in the frog

                  produces bile (stored in gallbladder)

          pancreas

     mesenteries - transparent membranes that surround body organs and attach them to the body wall

 

Respiration:

     4 structures which amphibians use to obtain oxygen -

          (1)  gills - used during the aquatic stage

          (2)  lungs - used by terrestrial adults

               lack a rib cage and diaphragm (fill their lungs by forcing air into them by lowering the floor of its mouth and swallowing air)

          (3)  the lining of the adult's mouth and throat

               has an abundant blood supply and can exchange gases

          (4)  the skin

               used especially in lungless amphibians

               also while an amphibian is underwater for a long period of time

               skin accounts for a great part of respiration

 

Circulation:

     3-chambered heart

     1 ventricle (pumps blood to all parts of the body)

     2 atria

          left atrium - oxygenated blood from lungs

          right atrium - deoxygenated blood from body

     dorsal aorta - largest blood vessel in the frog

     vena cava - largest vein in the frog

 

Excretion:

     kidneys (filter wastes and excess water and concentrate them in the form of urine)

     renal arteries / renal veins

     ureter

     urinary bladder

     cloaca

     anus

 

Responses:

     2 major divisions of the nervous system:

          (1)  central nervous system (CNS)

               brain and spinal cord

          (2)  peripheral nervous system (PNS)

               cranial nerves

               spinal nerves

               sensory organs

                    eyes - nictitating membrane - "third eyelid"

                    ear - tympanic membrane - "eardrum"

 

Reproduction:

     external fertilization

     male - testes produce sperm

     female - ovaries produce ova (eggs)

     mating process:  male crocks to attract a mate

                      she responds when her eggs are ripe

                      amplexus - in the water, the male clasps the female from behind which stimulates the release of eggs
                      (Latin - "embrace")

                      male covers the eggs with sperm

                      both parents usually abandon the eggs

          Although some female toads lay their eggs one at a time, most toads lay them in a long string, which they spread over plants in the water.  Frogs lay eggs in clusters, which are usually anchored to vegetation.  Some tropical species attach their eggs to the underside of leaves growing over water.  As the eggs hatch, the tadpoles drop into the water.  Even though some species lay thousands of eggs at a time (the arrow-poison frog lays a single eg), many eggs are eaten by larger water animals, and therefore only a few reach maturity.  The eggs are hatched in 2 to 25 days, depending on the water temperature; low temperatures slow down development.

          The American white-lipped frog lays its eggs in a hole near a pond, then whips the jellylike substance into a foam in which the tadpoles live until rain washes them into the pond.  The Surinam toad of South America lays its eggs and then quickly loops around to catch them on its back; they remain in cavities on the female's back throughout their larval sate.  The male midwife toad of western Europe carries the eggs wound around his hind legs.  When the eggs are ready to hatch, the male toad enters water and the tadpoles swim away.  After the female Darwin's frog lays eggs, the male frog picks up the eggs with his tongue and carries them around in his vocal sac, where they hatch and the young develop.  A few species lay their eggs on land under rocks, logs, or dead leaves.  These amphibians, such as the barking frog and the cliff frog that live on rocky cliffs in Texas, have no tadpole stage; they hatch from the eggs and begin life as a terrestrial animal.