MOLLUSCA 



i6i 



the stone to which she adheres. The octopus broods her eggs, 

 renewing the water around them by siphonal jets. 



Fossil Relatives. — As indicated on page 1 42, under Classification of 

 Mollusca, they are found from the Cambrian to the present, the La- 

 mellibranchs being especially abundant in the Cretaceous of America. 



Ancestry and Relationship to Other Phyla. — On account of the 

 occurrence of the trochophore larva the Mollusca are linked with the 

 worms. The Cephalopoda are separated from the other Mollusca, 

 having no free larvae and being provided with highly developed eyes 

 and nervous system. 



Economic Importance of Mollusca 



Class Positive 



Lamellibranchiata. i. As money. Quahaugs and cowries, i. 



1. Pearls. Pearl oysters, clams and 

 mussels. 



3. Buttons from mussel shells. 



4. As ornaments. 



5. Food — oyster, clam, mussel, scallop 



(adductor muscle), shells as chick- 2. 

 en grits. 



6. For roads (New England uses oyster 



shells). 



7. As church fonts — Tridacna (500 lb. 



shells). 



8. Window pane (Placuna). 



Negative 



a. Pholas — "borer." 

 b. "Ship-worms." 

 Teredo navalis and 

 Bankia fimbriata 

 attack wooden 

 ships and piles. 



Giant clam. Tridac- 

 na gigas (enemy of 

 divers). 



Gastropoda. 



I. For food or bait. Whelks, periwin- 

 kles, top shells, limpets, the aba- 

 lone (Haliotis). 



1. For buttons and as ornaments. 

 Ear shells, sea snails, cameo shells 

 (Cassis), top shells. Queen conch 

 shells {Strombus gigas) were for- 

 merly used in Liverpool for the 

 manufacture of porcelain. 



3. For dye stuffs the "sea hare" fur- 



nishes purple dye. "Tyrian pur- 

 ple" {Purpura, the whelk). 



4. For bird lime. The giant slug is 



used by South American Indians 

 to lime humming birds. 



5. The calcareous front doors (oper- 



cula) of some S. American gastro- 

 pods are sold for use in the U. S. as 

 "eye-stones." 



1. Boring gastropods at- 

 tack lamelli- 

 branchs. 



1. Destroy vegetables 

 and plants — gar- 

 den snail (slug) 

 Limax. 



3. Sometimes snails at- 



tack the eggs of 

 fish in nests. 



4. Intermediate hosts of 



larval stages of 

 flukes of man. 



