Larval form of mollusca

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

3. introduction Mollusca = mollis (L.) = soft bodies. 1 st 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. P reoral 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 P reoral ciliate area. V elum begin to protrude on both sides as a bilobed flap. V ery delicate. A nterior end of the larva provided with eyes and Tentacles. L arva has a shell. Velum is developed from the prototroch of the trochophore. Page 5

8. L arval 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. A nus is shifted to anterior side. F oot 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/mod/resource/view.php?id=85576 Invertebrate zoology book by barnes,fox,ruppert.