Class PISCES 



With paired fins; with or without scales; one occipital condyle; 



cold'hloodcd 

 Class AMPHIBIA 



Usually with one or two pairs of limbs; without scales; with 



two occipital condyles; cold-blooded 

 Class REPTILIA 



With or without limbs; with scales; with one occipital condyle; 



cold'blooded 

 Class AVES 



Fore limbs modified to form wings; with feathers; with one 



occipital condyle; warm-blooded 

 Class MAMMALIA 



With one or two pairs of limbs; with hair; with mammae; 



with two occipital condyles; warm-blooded 



KEY TO THE MINUTE AQUATIC ANIMALS 



1. One-celled or acellular animals, either separate or grouped together in 



colonies; no specialization of body cells of colonial forms, which are 

 usually spherical, disc-shaped or grouped at the end of a stem 

 Protozoa (Chapter 2) 

 Body made up of a number of cells, with some of the body cells differing 

 from others; usually with internal organs visible inside the body 

 wall 2. 



2. Animal partially or wholly enclosed within a shell 3. 

 No shell; animal sometimes living in a tube 4. 



3. Body soft, without legs 



Molluscs (Chapter 6) 

 With paired appendages, which may be completely withdrawn within 

 the shell, in some forms 



Arthropods (Chapter 7) 



4. With paired appendages 



Arthropods (Chapter 7) 

 No paired appendages; sometimes with setae or tufts of bristles along 

 the sides 5. 



5. Body segmented (segments sometimes evident only on the under side) 



6. 

 Body unsegmented 8. 



6. With a definite head, often darker than the body, and usually with 



external biting or sucking mouth parts 



Arthropods, Insect Larvae (Chapter 7) 

 Not so 7. 



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