GENERAL INFORMATION ABOUT MOLLUSKS 



To assure international understanding, Latin, a dead language, is used for the au- 

 thentic names of shells because it is not subject to change. Popular names are too 

 localized to be practical. You will not regret learning the scientific names from the 

 beginning. 



There are five classes of mollusks : 



1. Amphineura - the Chitons (coat-of-mail shells) have eight overlapping plates. 



2. Scaphopoda, the tooth-shells (tusk shells) are tubular. 



3. Pelecypoda - the bivalves, constitute about 18% of all mollusks. 



4. Gastropoda - the univalves, constitute about 80 % of all mollusks. 



5. Cephalopoda - the Squid, Octopus, Spirula and Nautilus. 



These five classes have but tvi^o structures in common - the foot and the mantle. The 

 foot does not have the same use in each class. The univalves creep by means of their 

 foot; the bival vales and tusk shells dig; and the Octopus envelopes its prey. The 

 mantle is the fleshy outer covering of the body which secretes the material form- 

 ing the shell. The color it secretes is usually similar to its own color and pattern. 

 Spines are formed by folds of mantle margin. Varices by thickening of previous 

 lips. 



As the tiny baby shell emerges from the egg sack it bears enough similarity in most 

 cases to its parent to be recognized. The baby shell forms the nucleus to which it 

 adds more shell material. In the univalves the evidence of this is apparent in the 

 axial ridges, the bivalves form concentric ridges each growth period. If the shell is 

 injured the mollusk repairs the damage but a scar or deformity will be apparent. 

 There will be an altered pattern. 



The color of the shells is influenced by light. Those living in the Littoral Zone, the 

 one with which we are most familiar (extending from shore to a depth of 100 fath- 

 oms) are colorful. Those dredged from the Archibenthal and Abyssal Regions are 

 white. No light penetrates these depths. The shells are thinner. The tons of pres- 

 sure would annihilate these creatures if it were not that the water is able to per- 

 meate all tissues, equalizing this pressure. 



Various species attain to different ages. Many are from one to fifteen years while 

 others rival man with three score years and ten. 



