A. Some major characteristics of amphibians

1.skeleton mostly bony, ribs present in some, absent in others
2. four limbs present some are limbless
3. skin smooth and moist with many glands
4. respiration by lungs (absent in some salamanders)
5. three chambered heart
6. ectothermal
7. excretory system of paired mesonephric kidneys, urea main nitrogenous waste
8.separate sexes (dioecious)

B. Classification
Three orders of amphibians

Order Caudata (salamanders, 400 species)

Habitat: terrestrial or aquatic
* Carnivorous during the larval and adult stages
*Walk with a side to side bending of the body
*Most salamanders have limbs of equal size set at right angles to the body
*Some salamanders with an aquatic larval stage hatch with gills which they lose later on during metamorphosis
*Others do not undergo metamorphosis but retain the larval features example, mud puppies

Order Anura (frogs and toads, 3500 species)

*Enlarged hindlegs provide better movement (hopping) than in Caudata
*Capture prey by flicking stick tongue
* Predator avoidance aided by camouflage
* Bright coloration in poison species

An animals nitrogenous waste is correlated with its habitat: Fig 44.13.  Page 937-938

• Ammonia is toxic and animals that produce this product need lots of water- common in aquatic species
• Urea is 100, 000 less toxic  than ammonia; produced by many land animals including some marine fishes.  More energy is required to produce urea.
• Uric acid nontoxic, largely insoluble in water and can be excreted as a semisolid.  More expensive to produce

REPTILES
 

1. Order Testudines (turtles)
2. Order Sphenodontia (tuataras) are lizard like found only around New Zealand.
3. Order Squamata (lizards and snakes)
4. Order Crocodilia (alligators and crocodiles) 4-chambered heart, oviparous
• Snakes have no eardrums but they are sensitive to ground vibrations
• Heat-detecting organs between the eyes and nostrils of pit vipers and rattlesnakes, are sensitive to minute temperature changes
• Snakes unlike lizards do not have moveable eyelids
• Most snakes are oviparous, most pit vipers are ovoviviparous a few snakes are viviparous

• Tubular fangs at the front of the mouth -vipers
•  short, permanently erect fangs venom injected by repeated bites -cobras, mambas, coral snakes

Some characteristics

1. Skeleton ossified, ribs with sternum, sternum absent in snakes.
2. Respiration by lungs no gills
three chambered heart four in crocodiles
3. Metanephric kidneys, Uric acid main nitrogenous waste,
4. Ectothermic, due to ectothermy, reptiles can survive on a much lower caloric intake than mammals of comparable size
5. Sexes separate, no larval stages

BIRDS

Some characteristics

1. Epidermal covering of feathers
2. Skeleton ossified with air cavities
3. Four-chambered heart
4. endothermic, feathers provide insulation
5. amniotic eggs
6. semisolid urine, uric acid main nitrogenous waste

more power less weight!!!!!!!

* Bones are light, delicate and laced with cavities
* Bird skull is built lightly and fused into one piece
* The vertebral column is rigid with most of the vertebrae fused together
* Sternum with large keel for the attachment of powerful flight muscles

Excretory systems in invertebrates and vertebrates

• Protonephridia in Flatworms- no internal openings
• Metanephridia  are more advanced found in Annelids and mollusks -two openings nephrostome collects fluid from the coelom and urine exits through nephridiopore
• Antennal glands in crustaceans are more advanced but they also lack open nephrostomes
• Insects and spiders have Malpighian tubules
• Hagfishes have the simplest kidneys among the vertebrates = pronephros (anteriorly situated)
• Adult lampreys, fishes and amphibians have mesonephros kidneys (centrally located)
• Reptiles, birds and mammals have metanepros kidneys

• During embryonic development, there is a succession of three developmental stages of kidneys: pronephros, mesonephros and metanephros
• Pronephros is the first kidney to appear and is located anteriorly functional kidney in hagfish
• It degenerates and is replaced by a more centrally located kidney the mesonephros during development
• The mesonephros is the functional kidney in embryonic amniotes reptiles, birds and mammals and adult adult sea lampreys, fishes and amphibians
• The metanephros, characteristic of adult amniotes is more caudally located and a much larger structure functional kidney in adult reptiles, birds and mammals

• In fish blood flows through 2 capillary beds this causes the blood pressure to drop considerably.
• Frogs with a 3- chambered heart and double circulation have a higher blood pressure as blood is pumped a second time after it loses pressure in the capillary beds of the lungs.
• Among crocodiles and all mammals and birds the left side of the heart receives and pumps only oxygenated blood, while the right side handles deoxygenated blood.

• Forebrain -cerebrum well developed in fishes, most complex in humans followed by porpoises
• Midbrain (brain stem)
• Hindbrain cerebellum = controls equilibrium its development is directly linked to the animals mode of locomotion. It is thus poorly developed in amphibians and reptiles, well developed in fishes and most complex in birds and mammals

• Statocysts are used for balance in invertebrates: Found in Cnidarians, Ctenophores, Mollusks, Crustaceans example; lobsters and crayfish have statocysts at the base of their antennules.
• In vertebrates, the organ of equilibrium are three semicircular canals and two small chambers (saccule and utricle). The saccule and utricle are static balance organs that like invertebrate statocysts, give information about the position of the head or body with respect to gravity


The blood of an insect does not play a role in oxygen transport. Insects have a very efficient respiratory system of tubes (tracheae, tracheoles and spiracles)