A seminar on the larval form of molluscan .it includes all the information about the topic . it is the best ever made article on this topic

1. A PROJECT ON
“THE LARVAL FORMS OF
MOLLUSCA”
BY-
Sambit Bhai Patel

2. CONTENTS
1. INTRODUCTION TO MOLLUSCS _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ page 1
2. TYPES OF LARVAL FORMS IN MOLLUSCS _ _ _ _ _ _ _ _ _ _ _ page 2
3. TROCHOPHORE LARVA _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ page 3
4. VALIGER LARVA _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ page 5
5. GLOCHIDIUM LARVA _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ page 7
6. CONCLUSION _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ page 9
7. SOURCE _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _page 10

3. introduction
• Mollusca = mollis (L.) = soft bodies.
• 1st used by Aristotle to the cuttle fish .
• Second largest phylum of animal
kingdom.
• Animal having soft bodies with in shell
and ventral muscular foot.
• Found in all possible habitat except in the
air.
• Most of them are marine.
• Dioecious or monoecious.
• Fertilization either internal or external.
• Development is either direct or indirect.
• Direct development -- no larval stage ,
indirect development– with larval stage.

4. Types of larva
• 3 types of larva are found in Mollusca.
TROCHOPHORE VELIGER GLOCHIDIUM

5. Trochophore larva
• Pear shaped.
• Measures about 0.5 mm in length.
• Circle of preoral cilia.
• Prototroch or velum divides the body into
two unequal parts.
• Upper one consist of prostomium.
• Lower part bearing mouth and anus.
• Preoral part is large and convex.
• Upper end consist of apical tuft.
• Prototroch is the swimming organ.

6. • Comprises mouth.
• Oesophagus.
• Stomach.
• Intestine (mesenteric).
• Sides of the mouth two ciliated elevations
present each consisting of a single cell.
• Lower end bearing a bunch of cilia called
“telotroch”.
• Generally planktonic and feeds on tiny
suspended particle, living or dead.
• Body divided in 3 regions -- pretrochal
-- pygidium
--growth zone.
• Pretrochal region consist of apical plate,
prototroch , the area surround the mouth.
• Pygidium consist of telotroch and the area
surrounding the anus.
• Growth zone lies between the mouth and
telotroch.
• The trochophore larva later develops into a
veliger larva

7. Veliger larva
• Preoral ciliate area.
• Velum begin to protrude on both sides as a
bilobed flap.
• Very delicate.
• Anterior end of the larva provided with eyes
and Tentacles.
• Larva has a shell.
• Velum is developed from the prototroch of
the trochophore.
Page 5

8. • Larval heart and kidney present which is
situated at the anterior end of the body
immediately behind the velum.
• Statocyst and gill-rudiments present.
• Long cilia of the velum function
Locomotion.
• suspension feeding.
• Alimentary canal is complete.
• Anus is shifted to anterior side.
• Foot usually bearing an operculum.
• During development of veliger larva
torsion occur.

9. Glochidium larva
• Glochidium larva enclosed by two valves.
• Each edge of which bears a hook.
• Shell valves cover a larval mantle.
• Bears four groups of sensory bristles.
• Rudimentary foot is present.
• Attached a long adhesive thread called
“Byssal thread”.
• Neither mouth nor anus.
• Measures from 0.1 mm to 0.5mm .

10. • Highly modified for a parasitic existence on
fish.
• They clamp on the body and other part of
the body.
• The larval mantle contains phagocytic cells
that feed on the tissue of host and obtain
nutrition for development.
• This period lasts for about 10-30 days.
• In the mean time the parasite is surrounded
by the overgrowth of skin of fish forming a
cyst.
• Some of the larger freshwater molluscans
may produce as many as 30,00,000
glochidia.

11. CONCLUSION
• Free-swimming larva are usually formed
when the adult is fixed.
• Internal parasites generally have a stage
which may be called larval stage in which
they are transferred either by active or
passive migration to a new host.

12. source
• Google
• Modern textbook of
zoology invertebrate book
by R.L. Kotpal.
• Biology of Mollusca book
by D.R. Khanna &P.R. Yadav.
• Wikipedia.
• www.biologyjunction.com/
mollusca
• ecoursesonline.iasri.res.in/m
od/resource/view.php?id=85576
• Invertebrate zoology book
by barnes,fox,ruppert.