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How to pronounce scaphopoda in English?

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It may seem that the snail has not much in common with the octopus, and the squid with the oyster,
but they do.
They are all mollusсs,
some of the most interesting and diverse groups of animals on the planet.
There are more than 100,000 known species of molluscs.
Despite their amazing diversity,
all molluscs share some unique characteristics that define their body plan.
First of all, all of them are invertebrates,
meaning, they have no back bone.
If they had one,
it would be very difficult, if at all possible,
for a snail to retract into its shell,
and for an octopus to squeeze through narrow gaps.
Secondly, all molluscs have soft and flexible bodies.
By the way, the name "mollusca" signifies "soft."
This is why most species grow a hard outer shell for protection.
The soft body of a mollusc
is covered by a structure called the mantle.
It protects the internal organs
and is responsible for secreting calcium carbonate,
the chemical compound necessary to build up the shell.
Most molluscs have a muscular organ called the foot,
that is used for digging, grasping, and creeping.
The tongue of molluscs also differs from the tongue of many other animals.
A unique organ, it is called the radula.
It is hard and rough like sandpaper,
and is used to scrape or rasp food.
Most species live in the ocean.
But not all.
Numerous molluscs also live in fresh water -
streams, rivers, ponds and lakes,
while others prefer humid areas on land.
Molluscs are among the earliest known life forms on Earth.
They probably evolved from primitive flatworm ancestors
more than 500 million years ago.
They successfully survived all the past geological periods,
although, of course, some species died out.
Those that exist today are divided into eight different classes.
Let's look at each one separately.
The first class is Caudofoveata.
These small, deep-sea animals have neither a shell nor a muscular foot.
The gills are located on the posterior end.
These species are generally characterized by their elongated worm-like bodies.
They are mostly burrowers
and orient themselves vertically,
with the gills at the entrance of the burrow.
The second class is Aplacophora.
They are also worm-like molluscs that lack shells.
The ventral surface has a median longitudinal groove.
This groove expands into an anterior pedal pit
and contains the narrow foot.
These small blind animals crawl along the bottom of the oceans
or live on corals.
The next class is Polyplacophora.
Members of this class are better known as "chitons."
They have a distinct dorsal shell formed by eight interlocking plates.
On their ventral body side, they have the head,
which is separated from the large and fleshy foot.
All chiton species are marine,
The fourth class is Monoplacophora.
These are molluscs equipped with cap-like shells.
The animal’s body is composed of the small head,
the mantle and the large flattened foot.
All their species are marine
and their habitats are limited to deep waters.
The fifth class is Scaphopoda.
Their shell is shaped like an elephant tusk.
This shell is open at both ends.
The head and foot extend through the ventral aperture of the shell.
The name "Scaphopoda" means "shovel-footed",
referring to the long, pointed foot.
The head bears numerous tentacles
that are used to detect and capture prey.
Most species burrow into soft sand,
leaving their narrow posterior end protruding from the surface.
The next class is Bivalvia.
Examples include mussels,
oysters,
scallops,
razor clams, and numerous other families.
For example, giant tridacnid clams.
They can grow to 1.5 meters in length
and attain a weight of around 200 kilograms.
The name "bivalve" means these molluscs have shells
that consist of two parts or valves.
Bivalves have a pointed, retractable foot
that protrudes from the shell.
Many species have two tubes, or siphons,
extending from the rear end.
Bivalves feed on fine organic particles floating in water.
Food particles collect on their gills.
When a small foreign object gets stuck between the mantle and shell,
the mollusc secretes layers of nacre around it.
As the layers of nacre gain in volume, a pearl grows.
The seventh class is Gastropoda,
the most diverse class of molluscs.
They have a large, flat foot.
The shell is most commonly coiled in a spiral.
Their shells have a variety of shapes and colours depending on species.
Some gastropods don't have shells at all.
As for their habitats,
gastropods live both in terrestrial and marine environments.
Finally, the last class of molluscs is Cephalopoda.
They lack the traditional foot,
instead they have eight or even more tentacles attached to their heads.
The mouth contains strong beak-like jaws.
Most of the members of this class lack shells.
In fact, the nautilus is the only extant cephalopod with a true external shell.
However, some cephalopods have a smaller internal skeleton.
Cephalopods move by jet propulsion.
Strong muscles fill the mantle cavity with water
and then quickly expel the water out of the siphon,
thus propelling the animal in the opposite direction.
To protect themselves from a great number of predators,
cephalopods such as squid and octopuses
can use dynamic camouflage to blend in with their surroundings on demand.
If the predator continues to approach,
some species are able to release a cloud of ink
to distract and confuse it.
Most molluscs are herbivorous.
Marine and freshwater species subsist on algae,
snails and slugs consume plants and fungi.
Octopuses, squid, and cuttlefish are primarily predatory.
Molluscs have contributed in numerous ways to the human civilization.
The Cowry shells were used as money by indigenous groups,
and oyster pearls have been treasured since time immemorial.
The Murex shells were used for the production of true purple,
and the cloaks of some rulers were woven from sea silk.
Finally, mollusks have been and still are
an important food source for modern humans.
Well, that seems to be all.
Now you know a lot about molluscs!
See you next time.