Molluscs are a diverse group of animals classified into three main types: bivalves, gastropods, and cephalopods. Bivalves possess two-part shells and use a foot shaped like a wedge for movement and digging, feeding by filtering water.
Hermaphrodite:
Are species in which all
individuals possess both
male and female sex organs.
Like gastropods.
Unisexual:
Are those in which individuals
have separate sexes. This means
that they are either male and female.
Like cephalopods and bivalves.
Gamete formation:
Are formed in the reproductive
system in organs called sex
organs or gonads.
Female gonads are called ovaries.
They produce feamle gametes or
ova, which are spherical, immobile
and larger than spermatozoa,
because they contain stores of
nutrients.
Male gonads
are called testes, that produce
male gametes and spermatozoa,
which are small, elongated
structures with a flagellum that
enables them to move.
Molluscs have sexual reproduction:
Is the most common form of
reproduction in animals. This type
of reproduction involves two
individuals of different sexes. A male
and a female.
Types of molluscs
Cephalopods:
Most of them do not have shell,
or just have a small internal shell,
called a gladius, which looks like
a sheet of plastic. In the head they
have two well-developed eyes and,
instead of a foot, they have a set
of tentacles around the mouth. They
are carnivores and active hunters.
Squids, octopuses and cuttlefish.
Bivalves:
Their shell is formed by two
valves, and they use muscles
to close these together. Their
foot, in the shape of a wedge,
is used to move and dig. Their
head is not well-defined. They
feed by filtering water and taking
tiny living things. Mussels, clams,
cockles, oysters and razor shells.
Gastropods:
Most of them have a sell
coiled in a spiral shape
They have large muscular foot to
move around. They have a
well-developed head. In their mouth
they have a scraper organ, called radula,
to feed themselves. Snails, slugs and limpets.
Nutrition
Digestive System:
Molluscs have digestive system.
1-The molecules in nutrients are
broken down through chemical
processes.
2-The nutrients are absorbed and
transported to the cell.
3-The unusable part of the food
is eliminated from the body.
Digestive track:
Are long tubes with one
opening for taking in food
and another opening for
expelling undigested food.
They have specialised
parts for carrying out the
different processes involved
in digestion.
Digestion:
Is a process carried out by
animals that consists of
transforming food to obtain
the nutrients it contains.
Feeding:
Consists of taking food
that is material from other
living organisms that contains nutrients.
Molluscs obtain food by
the tentacles.
