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Another well-known
variety is the gastropods or univalve mollusks. They have just
one shell that varies in size and shape from species to
species. Snails belong to this group and are the only member
of the mollusk family to be living in both land and water.
Then there are the
cephalopods with illustrious members like the octopus and
squid. Cephalopods are very active and have evolved out of
their need for shells for protection from predators. |
A snail is a univalve type of mollusk |
How the shells are
made
The mollusks’ blood is rich in calcium. The calcium is separated
from blood to crystallize and form calcium carbonate crystals. An
organ called the mantle plays the main role in the formation of the
shell. The crystals are deposited in layers that vary in thickness.
This layered formation adds to the strength of the shell. Various
factors like water temperature, alkalinity, acidity, the mollusk’s
diet, hormonal balance, etc. influence the process of shell
formation.
You may have seen and
wondered at shells of various hues. These hues are derived from
certain pigments found in the mollusk’s food. Its glands act on
these pigments and mix them with the hardening layers of shell. Some
beautiful color effects can also be seen due to light being
refracted of the various layers.
What the shells tell
us
The shape, construction, color and ridges on a shell can tell
us a lot about the shell’s owner. A low and wide shell indicates
that the mollusk is subject to strong waves. A thinner spherical
shell points out that the owner comes from deeper water or maybe
from the poles. Water in these areas is not so rich in calcium, the
factor that accounts for the thin shells. Coiled or flat saucer-like
shells indicate that the mollusk inhabits hard seafloors. Mollusks
that come from places with uneven jagged rocks will have expanded
shell edges that make moving in such areas easy. Some features give
the mollusks a look that makes them look more formidable than they
really are – Mother Nature’s camouflage kit. Mollusks that need to
move around and even burrow into soft and sandy surfaces have
smooth, long tapering shells.
Mollusks and man
And what do you think is the main difference between mollusks
and us? Our soft bodies protect our skeletons whereas their
skeletons protect their soft bodies! |
