Lecture Slides on Archachatina marginata ZLY 201

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Biology of Archachatina
ZLY 201
SHITTU, O.
Zoology, Unilorin
Description of the Shell
Shell Structure & Formation
Body Shell Plan
The process of torsion
Coiling in Gastropoda
 Early gastropods had all the whorls lined in a single plane i.e.
had a planospiral shell and were bilaterally symmetrical.
 Today, gastropods exhibits a conispiral shape i.e. each
succeeding wall is at the side of the preceding one.
 With conispiral shape, the animal had to redistribute it
weight by shifting the shell upward and posteriorly.
Coiling in Gastropoda
The shell axis now appear
oblique to the longitudinal
axis of the foot.
 Weight and main body
whorl pressed on the right
side of the mantle cavity.
 Loss of the gill, auricle &
right kidney leading to
bilateral asymmetry.
 Fouling eventually avoided
as water enters the left and
lives by the right through
the
anus
and
nephridiopore
Ctenidia loss in Gastropoda
• The Pulmonata show some detorsion, therefore has lost their
ctenidia thereby making the vascularized mantle wall
assuming a lung function by contraction of the mantle floor.
• The anus and nephridiopore opens near the pneumostome
expelling wastes via water from the lungs.
• Archachatina has two pairs of tentacles with the posterior
one bearing the eyes.
Position of the eye
•
Archachatina Anatomy
Position of the lung
showing pneumostome
Archachatina Anatomy
• They have a single nephridium
(kidney).
• The circulatory and nervous system
are well developed. The nervous
system has three pairs of ganglia
connected by nerves.
• Sense
organ
includes
eyes
(photoreceptors, statocysts, tactile
organs & chemoreceptors)
• The eye cup contain a lens covered
with a cornea.
• The osphradium situated at the base
of the incurrent siphon is sensory in
function (chemoreceptor)
Archachatina Anatomy
Radula
• This is a rasping, protrusible, tongue
like organ. It is a ribbon-like
membrane on which rows of tiny
teeth pointing backward are
mounted. Complex muscles move
the radula and odontophore in and
out so that the membrane rotates
over the cartilage tips (250,000).
The radula rasp off fine food
particles and conveys it towards the
digestive tract.
• The pattern and number of teeth in
a row determines the speciation.
Reproduction in Archachatina
• They are monoecious, undergoing intracapsular(direct)
development instead. Fertilization is internal. They are
ovoviviparous, brooding their eggs in the pallial oviduct
Adult snails Mating
Shedding of
Eggs
End of Presentation
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