190 BIOLOGY FOR BEGINNERS 



port, pp. 120-152; Economic Zoology, Osborne, pp. 174-200; Economic 

 Zoology, Kellogg and Doane, pp. 106-125; Applied Biology, Bigelow, pp. 

 358-376; Life and Her Children, Buckley, Chap. VIII; Animal Life, 

 Thompson, p. 25; Seashore Life, Mayer, pp. 77-112; Life in Ponds 

 and Streams, Furneaux, pp. 179-200; Talks About Animals, pp. 3-45; 

 The Crayfish: an Introduction to Zoology, Huxley, entire; Practical 

 Zoology, Davison, Chap. IX. 



SUMMARY 



Contrast, worms, having only simpler tissues and organs, no skeleton, 



inactive. 



Crustacea, with high specialization, skeleton, active, aquatic. 

 Characteristics: 



External skeleton adapted for protection. 

 Jointed appendages adapted for rapid motion. 

 High specialization adapted for division of labor. 

 Gills and connected organs adapted for aquatic life. 

 Crayfish (as type of Crustacea). 

 External Structure: 



Exo-skeleton, for protection and to act as levers for muscles. 

 Protective adaptations: 

 Hard, limy, color, spines, 

 Projection over gills and abdomen. 

 Carapace, rostrum. 

 Lever adaptations: 

 Hollow, strong, light, 

 Hinge joints in all directions. 

 Body regions, cephalo- thorax and abdomen. 

 Cephalo-thorax : 



Includes head and thorax, 13 segments, 

 United for strength, rostrum for protection. 

 Carapace over anterior and gills. 

 Head appendages: 

 Sense organs. 



Antennules, antennae, for feeling or smell. 

 Eyes, ear sacs, sense hairs. 

 Mouth parts. 



Mandibles, one pair for chewing. 

 Maxillae, two pair aid in holding food. 

 Maxillipeds, three pair, catching and chewing food. 

 Thoracic appendages. 



Maxillipeds, three pair, holding and chewing food. 

 Large claws, defence and food getting. 

 Clawed feet, two pair, locomotion, prehension. 

 Unclawed feet, two pair, locomotion. 

 (Gills on all above appendages.) 



