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(Fishes, Amphibians, Reptiles)

"Vertebrates" means animals with backbones, composed of individual bones called vertebrae. "Cold blooded" means they do not control their body temperature, so it changes with their surroundings.


1) Body covered with slimy SKIN, due to mucus produced by special glands, and usually SCALES.

2) Entire LIFE CYCLE spent in water. Usually, FERTILISATION is EXTERNAL, i.e. in water, and MANY SMALL eggs are laid and left. This may be wasteful, but sometimes they lay a few larger eggs with more food supply, or eggs may be laid in nests, guarded by one or both parents, or kept inside female's body (ovoviviparity). Many different types of eggs. Development of embryo within egg may take a long time, depending on environmental conditions.

3) Inhabit ALL SORTS of WATER - fresh & salt - hot & cold .

4) TEETH, if present, are modified SCALES.

5) "COLD BLOODED" - same temperature as water. Most extract DISSOLVED oxygen from water by means of gills .

6) Many variations on basic body shape. BASIC BODY SHAPE provides streamlining , and variations may result from loss of this need.

- Bottom-dwelling (soles, plaice, etc.): flattened

- Eels, etc. : elongated for movement through weeds and mud.

7) Main subdivisions (classes) - [also primitive jawless class]:

- " BONY FISH" - most common fish : BONY SKELETON, SWIM BLADDER to control BUOYANCY, OPERCULUM covers gill slits, even tail lobes

- " GRISTLY FISH" - e.g. sharks, rays, skates (more primitive) : SKELETON of CARTILAGE, no swim bladder (tend to sink), unprotected gill slits, uneven tail lobes, underslung mouth, fleshy fins.

8) Differences between sexes most noticeable in solitary types.

9) Usually NO PARENTAL CARE of young, but in some species male or both parents guard eggs or fry.

10) MOVEMENT: PROPULSION by waves of contraction of muscles of body and tail, STABILISED by single FINS in mid line of body, STEERED by movement of paired FINS (same position as limbs).

11) LATERAL LINE is special SENSE ORGAN - responding to vibrations in water (equivalent of EAR in higher animals).

Label this diagram of the external features of a fish.

Fish (herring actually) - unlabelled

The gills of a fish are used to absorb oxygen (in solution - not from splitting H2O !) from the surrounding water. It swallows fresh (oxygenated) water and passes it over the gills, in a one-way flow. As the water leaves, the fish also gets rid of carbon dioxide, which passes into the water it breathes out.

Complete and annotate these diagrams to show the process: animation

Use the outline of a fish's body to show, in a diagrammatic form, how blood is pumped by the simple heart so that it circulates through the gills and supplies the rest of the body with oxygen, as well as removing carbon dioxide.


1. Body covered with soft, MOIST skin , slimy due to mucus secreted by special glands. NO SCALES. Oxygen taken in through skin (also maybe lungs and gills). Skin is not "waterproof" - dehydration a problem.

2. Adults live in water or on land, USUALLY CLOSE TO water , but most return to water to lay eggs. Large numbers of eggs, without shell. Fertilisation is external. Most of development of young (tadpoles = larvae) occurs in water. "metamorphosis" - complete change.

3. Inhabit wetter areas - ponds, lakes, marshland, tropical rainforest - or cold damp places. Distribution limited by water loss.

4. Teeth absent or small - for gripping only. Frogs and toads have very mobile tongues.

5. COLD-BLOODED: 3 chambered heart.

6. RESPIRATORY SURFACES: gills in larvae, also SKIN and LUNGS - no active chest movements.

7. Three groups, each with BODY FORM well ADAPTED to their environment:

a) NEWTS, SALAMANDERS, AXOLOTLS - mainly aquatic (in water) - long tail and short limbs

b) FROGS and TOADS - mainly terrestrial (on land) - tail lost, hindlegs developed, eyes forward, stiff neck.

c) APODANS (Caecilians) - terrestrial burrowing group - legs much reduced - few details known.

8. Usually no parental care of young, but there are noteworthy exceptions, showing a range of different adaptations.


1. Body covered with TOUGH dry SCALES.
Function: to prevent dehydration, and abrasion.

2. Reproduction usually by means of EGGS - with leathery SHELL (smaller than birds' eggs) - eggs usually "abandoned". Some species show ovoviviparity.

3. Normally inhabit land and water, especially hotter regions. Extinct pterodactyls flew in air.

4. Teeth variable - see groups in 10.

5. COLD BLOODED - bask in sun to warm up for maximum efficiency, inactive in cold conditions. HEART has only 3 CHAMBERS.

6. Breathing by lungs.

7. CLOACA is opening of urinogenital and digestive systems.

8. (External) differences between sexes is only slight.

9. Parental care not advanced. Parents may guard eggs or "hatchlings", but do not "raise" young.

10. Four main groups today - 12 have become extinct: