oyster. The oyster quickly snaps shutits double shell and holds it firmly
closed. The muscles of the oyster are verystrong, so the shell stays closed
tightly. You might think that closing his shell would protect the hapless
victim, buteventuallyhe has to open it sothathe can "breathe." Bytaking
inwaterandtakingfrom it the oxygen he needs, the oyster stays alive.
As soon as the starfish feels the muscles of hisfuturemeal relaxing, he
relaxes his own gripbutstillremainswrappedaroundthe oyster. When the
i~ space between the twooystershells is largeenough,the starfish quickly invertsr
' (turns inside out) his stomach through his mouth opening and pushes it
between the parted shells. The strange"inside-out"stomachof the starfish
producesjuicesthatquickly digest and absorbthe soft body of the oyster.
His meal completed,the starfish withdrawshisstomachand crawls away to
enjoy anafter-dinnerrest. Allthatremainsof theoysteris a pair ofempty
shells.THE OYSTER AND THE PEARL
Materials:Get a live oyster from a fishmarket.
Follow thisprocedure: Examine the oyster.
You will observe:The living, fleshypartofan oyster is soft and boneless.
This is also true of the bodies of his close relatives, the clam, the scallop, the
mussel and the snail. The outershellsoftheseanimals provideshelterand
protectionagainstotherseaanimals.Usually the oyster can washouta grain ofsandor the hardshell of a
much smaller animalthatmight be swept into his own shell by the water.
Butsometimesa grain of sand or a tinyhardshell gets stuck between his shell
and the oyster'ssoft body. This irritatesthe oyster. The soft tissuearound
theirritatingobject secretes a liquid called nacre or "mother-of-pearl." This
liquid flowsaroundthe grain of sand andhardensto form asmoothprotective
layer over it.
The oyster continuessecreting layer uponlayer ofmother-of-pearluntil
a maturepearlis formed. Ittakes a longtime-perhapsas long as five to ten
years-fora pearlto beproduced. Ofcourse, the sizeofa pearldependson
how long itremainsamongthe secreting tissues of the oyster.
The hard, glistening, irridescent inner surface of the oyster's shell is
mother-of-pearl,too. Itprovidesa thickcoatingtoprotecttheanimal'ssoft
body from whatwould otherwisebe aroughshell surface.