WEEK 12 - Mother Pearl Flashcards
What Is Mother of Pearl Made Of?
Shiny inner layer of seashells = mother of pearl
Real name = nacre
What is nacre?
Nacre is made by molluscs, including:
- Bivalves (e.g. clams, mussels, oysters)
- Gastropods (e.g. snails, abalone, turban shells)
- Cephalopods (e.g. Nautilus, extinct ammonites)
What Key Feature Do All Molluscs Have?
Fleshy foot
Radula (rasping organ)
Digestive system
Gills
Mantle (key part for shell/nacre!)
What is mantle?
- Fleshy membrane around internal organs (“visceral mass”)
- Mantle is what produces nacre (mother of pearl)
What Does the Mantle Do in Shell Construction?
- Protects internal tissues
- Secretes the shell (in shelled molluscs)
Mollusc examples:
- Gastropod (snail) → has a shell
- Bivalve (clam) → has a shell
- Cephalopods:
–> Squid → no outer shell (“naked”)
–> Nautilus, ammonites → have shells
What does the mantle secrete to build the shell?
- At the edge of growth, the mantle secretes prisms of calcium carbonate
- Made of aragonite or calcite
What forms the mother of pearl layer?
- After the prismatic layer, the mantle adds aragonite nacre tablets
- This creates the nacreous (shiny) layer = mother of pearl
What happens when the mantle isn’t building shell?
- The mantle separates from the shell
- Shell growth only happens when mantle is touching the shell
What are the two layers of a mollusc shell?
- Prismatic layer – outer layer
- Nacreous layer – inner, shiny layer (mother of pearl)
What is the periostracum?
- Organic layer that covers the prismatic layer
- Found on the outside of mollusc shells
What is the function of the periostracum?
- Protects shell from dissolution (wearing away)
- Helps with camouflage
Why is the shell’s outside not shiny?
- The periostracum is dull and rough
- It hides the shiny nacre inside
- “Don’t judge a book by its cover” applies here!
What is the prismatic layer like?
- Made of blocky calcite or aragonite
- Dull, weakly translucent to opaque
What is the nacreous layer like?
- Made of flat aragonite tablets
- Shiny, colorful, and translucent
- Called mother of pearl
Why is the nacreous layer smooth?
- Lets the mantle slide over it
- Prevents damage to the tissue
What is nacre made of?
- Aragonite crystals (82-86%)
- Conchiolin (organic substance, 10-14%)
- Water (2-4%, most is in conchiolin layers)
What is aragonite in nacre?
- Forms the framework of nacre
- Crystals give nacre its strength and appearance
What is conchiolin in nacre?
- A complex organic substance
- Made of polysaccharides (sugars) and protein fibers
What is the structure of nacre?
- Aragonite tablets form the framework
- Conchiolin holds tablets together
How are aragonite tablets arranged in nacre?
- Tablets are glued to each other with conchiolin
- Can form thicker sheets with conchiolin layers in between
What happens to conchiolin in the sample?
- Conchiolin is dissolved in SEM samples to show aragonite tablets
- Conchiolin binds tablets together in natural structure
What is observed in a plan view of nacre?
- Hexagonal shapes of aragonite tablets
- Partial overlap of aragonite sheets, like shingles
How do aragonite sheets overlap in nacre?
- Aragonite sheets do not uniformly cover the surface
- They partially overlap like shingles
