COLLEGE ZOOLOGY 



nautili, cuttlefish, and octopi; the phylum 

 includes at least 90,000 species. An organ 

 characteristic of most of them is a muscular 

 foot that usually serves as an organ of loco- 

 motion. An enclosing envelope, the mantle, 

 is also present. The soft body of many mol- 

 lusks, such as the oyster and snail, is pro- 

 tected by a shell of calcium carbonate which 

 is secreted by the mantle. 



10. Phylum Echinodermata 



A characteristic of most members of this 

 group (5000 species) is a spiny skin. It in- 

 cludes the starfishes, brittle stars, sea urchins, 

 sea cucumbers, and sea lilies. All are marine 

 in habit and radially symmetrical; a skeleton 

 of calcium carbonate is often present. Loco- 

 motion is usually accomplished by means of 

 tube feet. 



11. Phylum Chordata 



Except for a few primitive species, the 

 chordates (65,700 species) are vertebrates; 

 that is, their axial support is made up of 

 small bones or vertebrae and is known as the 

 vertebral column, or backbone. Vertebrates 

 are the most highly developed of all ani- 

 mals. They may be divided into 7 classes as 

 follows: ( 1 ) the cyclostomes or lamprey eels 

 and hagfishes, (2) the cartilaginous fishes, or 

 sharks and rays, (3) the common bony 

 fishes, (4) the amphibians or frogs, toads, 

 and salamanders, (5) the reptiles or alli- 

 gators, lizards, snakes, and turtles, (6) the 

 birds, and (7) the mammals or four-footed 

 animals. The birds and mammals differ from 

 the others in that they are warm-blooded; 

 that is, their body temperature is constant 

 and about 100° F, regardless of the tempera- 

 ture of the surrounding medium; whereas 

 reptiles, amphibians, fish, and other animals 

 are called "cold-blooded" because their body 

 temperature varies with that of their en- 

 vironment. Actually, cold-blooded is a poor 

 name to apply to these animals, for in sum- 

 mer the blood of a grasshopper may be 

 warmer than that of a man. These so-called 

 cold-blooded forms are really animals with- 



out a temperature-controlling mechanism. 

 The headpiece at the beginning of this 

 chapter helps us to realize how varied ani- 

 mal life is, but only a study which we 

 are going to make of each of the 11 phyla 

 just described can furnish a true idea of the 

 remarkable diversities exhibited by the hun- 

 dreds of thousands of different kinds of 

 animals. 



Unity of animal life 



There is a tremendous variety of animal 

 life among the more than one million dif- 

 ferent species, yet all these exhibit some fea- 

 tures in common. Some common charac- 

 teristics will be mentioned here, but they 

 cannot be appreciated fully until they are 

 studied later in more detail. Many of these 

 characteristics are similar to those of plants 

 and to those of nonliving matter, but when 

 taken together they furnish a means of dis- 

 tinguishing animals from all other things. 



Composition 



The essential substance of which all plants 

 and animals are composed is known as pro- 

 toplasm. Nonliving things do not contain 

 protoplasm. 



Structure 



The protoplasm in plants and animals is 

 divided into units called cells; nonliving 

 things are not divided into cells. 



Form 



Animals are so constant in form that they 

 can usually be distinguished from one an- 

 other by this characteristic alone. Plants are 

 less constant in form, but more so than most 

 nonliving things. 



Movement 



Animals can move their parts, and most of 

 them are capable of locomotion. Plants, with 

 few exceptions, are incapable of locomotion, 

 and the same is true of nonliving things. 



