278 HOW DO WE CLASSIFY ANIMALS? 



II. The protozoans (6) always have cilia; (7) are single-celled 

 animals; (8) never live in the water; (9) reproduce by dividing; 

 (10) reproduce by budding. 



III. The coelenterates (11) live in the ocean; (12) have baglike 

 bodies with a mouth at one end; (13) are usually fixed and do not 

 move from place to place ; (14) may show an alternation of generations ; 

 (15) include corals, sea anemones, and hydra. 



IV. The arthropods (16) have no definite number of legs; (17) al- 

 ways have a limy shell; (18) have an exoskeleton; (19) have jointed 

 legs and jointed body; (20) have compound eyes. 



V. Mollusks (21) are soft-bodied animals; (22) always have a 

 shell ; (23) usually have a shell ; (24) live only on land ; (25) include 

 snails, oysters, clams, and squids. 



VI. Fishes (26) are the only animals that live in the water; 

 (27) have their limbs modified into fins; (28) breathe by taking 

 oxygen out of water by means of gills ; (29) use the ear as a balancing 

 organ ; (30) lay many eggs which are fertilized outside the body. 



VII. Amphibians (31) include turtles, snakes, and tortoises; 

 (32) always have moist skin with no scales in it ; (33) often undergo 

 a metamorphosis, part of the life being in the water and part on land ; 

 (34) always have both lungs and gills at the same time in their life 

 history ; (35) include the toads, frogs, and salamanders. 



VIII. Reptiles (36) have no teeth; (37) are never poisonous; 

 (38) always have scales on the skin; (39) always breathe by lungs; 

 (40) show their relationship to birds by laying eggs with shells. 



IX. Birds (41) show, by scales on their legs, relationship to reptiles ; 

 (42) have modified arms or forelegs which are used in flying ; (43) al- 

 ways build a nest in which are laid many eggs ; (44) have a four- 

 chambered heart ; (45) have a skeleton composed of light and hollow 

 bones, with large breastbone to which wing muscles are attached. 



X. Mammals (46) are at the top of the evolutionary scale ; (47) have 

 a four-chambered heart, a more or less heavy covering of hair, and 

 suckle their young ; (48) always stand erect ; (49) are found as the 

 most recent fossils ; (50) include man. 



Achievement Test 

 1. What is the name of at least one animal from each of the phyla 

 of the invertebrates and the vertebrates ? 



