646 



APPENDIX B 



latter closely analogous to but not homologous with the eyes of vertebrates; 

 mouth with horny jaws and a rasping tongue like that of the snails; foot trans- 

 formed into a ring of arms or tentacles surrounding the mouth, prehensile and 

 often furnished with sucking disks and hooks; the mantle muscular, its cavity so 

 arranged that the water contained in it can be squirted out through a "funnel" 

 or "siphon," thus propelling the animal backward. The earlier forms all covered 

 with a straight-conical or coiled, chambered shell ; shell reduced or absent in most 

 modern forms. 



The fossil record of this group is unusually complete (Figs. 27.7 and B.14). 

 Surviving cephalopods are the squids, cuttlefishes, nautilus and octopus. These 



Fig. B.15. Burrowing and tube-dwelling marine worms in a section of sandy sea floor at 

 Woods Hole, Mass. In the cavity at the left are the clamworm, Nereis virens (stout-bodied), 

 and Arabella (slender) ; the proboscis worm, Rhynchobolus or Glycera, is also seen with its 

 four-fanged pharyngeal proboscis extended as in catching prey. At the right is the U-shaped 

 tube of the parchment worm Chaetopterus. This worm has some of its segments shaped 

 like pump valves, and by means of them pumps a food-and-oxygen-bearing stream of 

 water through the tube. Within the loop of the tube is Phascolosoma, one of the Sipunculida, 

 a group of uncertain zoological relationships. All the others are Annelida. (Courtesy Ameri- 

 can Museum of Natural History.) 



are among the most peculiar and fascinating of animals. Some of the deep-sea 

 squids are the largest of all invertebrates. 



Many of the mollusks are of economic importance. Some are eaten (oysters, 

 clams, scallops); the shells of others are used for making buttons and for other 

 commercial purposes; and the pearl oysters are the basis for an important indus- 

 try. About 80,000 modern species of mollusks have been described, and fossil 

 forms are extremely numerous. The snails appear to be the largest group in 

 existence today and are now at the climax of their development. 



Phylum IX. ANNELIDA (an neT i da; Latin, annelus, "ring"). 



Segmented worms such as earthworms, marine worms, and leeches. 

 Highly developed intermediate Metazoa, typically exhibiting the follow- 

 ing characters. 



