The Garden Snail
||- soft bodied animals with chalky shells
||- broad flat muscular foot
||- refers to the helical coil of the shell
||- the common garden snail (cf the edible snail - Helix pomatia)
The garden snail is a herbivore
The mouth has a ribbon-like rasping
tongue called a radula.
The radula is covered with fine horny
curved teeth. The radula is rubbed back and
forth against the leaf and tears off small pieces of vegetation in a similar manner to the
action of a rasp.
The crop contains symbiotic
bacteria which digest the cellulose in the plant matter.
Useful food material is absorbed in the
Undigested food passes out the anus.
and gas exchange:
The snail has a simple lung.
The opening to the lung can be open and
closed by a muscular valve - the closing of the opening helps reduce water loss.
The diaphragm is used to fill the lung
with air and helps force oxygen into the blood
O2 is carried away from the
lungs in the blood. In molluscs O2
is carried by haemocyanin (similar to haemoglobin in mammals).
CO2 passes from the blood to the air in the lungs and
is exhaled when the valve opens again.
Snails have an open circulatory system
with a simple two chambered heart.
The heart pumps the blood into the
aorta and then into smaller arteries. From
these it empties into the body cavity. This
cavity is called the haemocoel.
The blood is bluish due the
The blood passes from the body cavity
into vessels surrounding the lung where O2 is absorbed and CO2 is
released from the blood.
The blood re-enters the heart via the
Sense organs are eyes sensitive to
light and dark - they are on the long tentacles.
Chemosensors are found on the
Snails have no hearing.
Ganglia (singular = ganglion)
contain groups of nerve cells.
The cerebral ganglion acts as a 'brain'
The pedal ganglion coordinates
The senses and ganglia are concentrated
at the front of the body - this helps the snail to sense and react to danger as fast as
The blood in the haemocoel helps
support the internal organs.
The shell is made of Calcium carbonate
and provides camouflage, protection, and some support of internal organs.
The snail moves by ripples of muscle
contraction moving down its foot. There is a
gland behind the mouth which releases mucus to reduce friction and prevent damage to the
The shell grows from the outer rim
where it joins to the mantle. The shell is
wound around a central support called the columella.
Excretion is the removal of waste
products from cell reactions.
CO2 is excreted through the
A kidney-like organ removes nitrogen
containing wastes and changes them to uric acid which is then excreted.
Uric acid is insoluble and so does not
use water when it is excreted - this is important to help conserve water.
have an ovotestis which produces both eggs and sperm cells.
occurs after stimulation from a 'love-dart'. Small packets (= spermatophores)
containing the sperm are exchanged between snails.
ovotestes now produce eggs which are fertilised by the sperm in the spermatophores.
The eggs are laid on the ground or in litter.
niche and environment:
Habitat is the place where an
organism lives. eg the snail lives in grass, hedges, gardens
Niche is the role of an organism
in its community. The niche also includes the
adaptive features the organism has which help it to survive and fulfil its role in the
eg The snail's niche is as a herbivore, it provides food for birds and hedgehogs, it is a
pest to humans. A few of its major adaptive
features are a hard shell, rasping radula and mucus producing gland.
is the conditions in which the organism lives. This can include the effects of both
living and non-living things.
eg. The snail's environment is cool, dark and moist.