MOLLUSCA
PHYLUM MOLLUSCA ( by: Geonyzl  J. Lepiten
Mollusca <ul><li>-  from the Latin word “ Mollis”  meaning  soft.   (From the Latin  Molluscus  meaning soft of body)   </...
<ul><li>  -  Class Gastropoda </li></ul><ul><li>  - Class Pelecypoda (Bivalva) </li></ul><ul><li>  - Class Cephalopoda </l...
Anatomical features: <ul><li>Flexible body wall, that surrounds the body. </li></ul><ul><li>It varies from some species to...
<ul><li>Some part of the wall was used for locomotion, food entrapment, and prevention of water loss. </li></ul><ul><li>Mu...
B. The Shell <ul><li>It is formed by secretions of glandular cells in the  mantle. </li></ul><ul><li>The thin outer layer ...
Digestive tract <ul><li>It is complex and complete. </li></ul><ul><li>The foregut region consist of an esophagus, stomach ...
 
<ul><li>Is through the gills called CTENIDIA. (located in mantle cavity) </li></ul><ul><li>Excretion of waste through the ...
The Circulatory and Nervous System <ul><li>Blood circulates through the gill filaments. </li></ul><ul><li>Most mollusk blo...
<ul><li>Blood circulation would vary and it is mediated by a muscular heart. </li></ul><ul><li>It also possess well-develo...
Reproduction <ul><li>Reproduction is sexual. </li></ul><ul><li>The fertilized egg develops into a swimming form called TRO...
Class Gastropoda <ul><li>From the Greek word “Gastro + poda” means stomach foot. </li></ul><ul><li>DEFINING CHARATERISTICS...
(Class Gastropoda…….) <ul><li>Most of the approximately 40,000 living species of  gastropods  have shells. </li></ul><ul><...
<ul><li>Forms without shells are called &quot;slugs“ </li></ul><ul><li>However the terrestrial slugs are not  closely  rel...
ANATOMY OF THE GASTROPOD WITH SHELL
Class Pelecypoda (Bivalva) <ul><li>The  bivalves   include forms such as  clams  ,  mussels  ,  scallops  ,  oysters  , as...
<ul><li>Bivalves  are laterally compressed animals, with two shell &quot; valves  &quot; that are hinged on the animal's d...
Continue on Bivalva…… <ul><li>Bivalves  are found in just about every marine environment, from the  intertidal   zone to t...
<ul><li>Most  bivalves  are suspension feeders, filtering small organisms and organic particles from the water (such as  b...
 
after Brusca & Brusca 1990 Left Valve and Dorsal View of a Clam Shell
Bivalve continue… <ul><li>The shell is made up of  three layers :  </li></ul><ul><li>The  periostracum  or thin outer laye...
<ul><li>the prismatic or thick middle layer that is made up of calcium carbonate crystals arranged in vertically,  </li></...
 
Bivalve continue…… <ul><li>Food entering the mouth is passed anteriorly to the stomach via ciliary action. </li></ul><ul><...
<ul><li>This dorsal portion of the stomach is lined with chitin except for the large folded and ciliated sorting region, i...
Members of the Class Bivalva A scallop  Tridacna (Tridacna)  gigas  Pharella javanica
Class Cephalopoda <ul><li>Cephalopods  , which include the familiar  squids  and  octopus   include species which are the ...
<ul><li>There are also forms with external shells ( nautilus  ), and internal hard shells ( cuttlefish  ).  </li></ul><ul>...
(continue on Class Cephalopods……) <ul><li>Cephalopods  have a  closed  circulatory  system, an adaptation to their active ...
<ul><li>Squid  in particular are often very abundant in  pelagic  marine environments, where they are voracious predators ...
Anatomy of the Cephalopods
Class Aplacophora <ul><li>250 living species (poorly studied!) of marine, wormlike,  </li></ul><ul><li>bilaterally symmetr...
<ul><li>The foot is restricted to an anterior pedal shield or to a narrow groove running the length of the body. </li></ul...
Summary <ul><li>Characteristics of Mollusca:-   </li></ul><ul><li>Bilaterally symmetrical.  </li></ul><ul><li>Body has mor...
<ul><li>Body without cavity.  </li></ul><ul><li>Body possesses a through gut with mouth and anus.  </li></ul><ul><li>Body ...
<ul><li>Has a nervous system with a circum-esophageal ring, ganglia and paired nerve chords.  </li></ul><ul><li>Has a true...
<ul><li>Has a pair of kidneys.  </li></ul><ul><li>Reproduction normally sexual and gonochoristic.  </li></ul><ul><li>Feed ...
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Mollusca 3

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Mollusca 3

  1. 1. MOLLUSCA
  2. 2. PHYLUM MOLLUSCA ( by: Geonyzl J. Lepiten
  3. 3. Mollusca <ul><li>- from the Latin word “ Mollis” meaning soft. (From the Latin Molluscus meaning soft of body) </li></ul><ul><li>- first used by Curvier in 1798. </li></ul><ul><li>- one of the most successful groups in the animal kingdom. </li></ul><ul><li>- found in all habitats </li></ul><ul><li>- divided into 8 classes: </li></ul>
  4. 4. <ul><li> - Class Gastropoda </li></ul><ul><li> - Class Pelecypoda (Bivalva) </li></ul><ul><li> - Class Cephalopoda </li></ul><ul><li> - Class Aplacophora </li></ul><ul><li> - Class Monoplacophora </li></ul><ul><li> - Class Polyplacophora (Chitons) </li></ul><ul><li> - Class Scaphopoda (Tusk Shells) </li></ul><ul><li> - Class Cuadofoveata </li></ul>
  5. 5. Anatomical features: <ul><li>Flexible body wall, that surrounds the body. </li></ul><ul><li>It varies from some species to species , some part of the wall were folded to form a MANTLE . </li></ul><ul><li>In some species, part of the wall formed into a SHELL </li></ul><ul><li>On the underside the wall is stretched to form a thickened mass called the foot. </li></ul>A. The Body Wall
  6. 6. <ul><li>Some part of the wall was used for locomotion, food entrapment, and prevention of water loss. </li></ul><ul><li>Muscle tissue is present (but much more found in the foot since it is used for locomotion). </li></ul>
  7. 7. B. The Shell <ul><li>It is formed by secretions of glandular cells in the mantle. </li></ul><ul><li>The thin outer layer is known as periostracum which is composed of organic layer. </li></ul><ul><li>A thin innermost calcareous layer known as nacreous layer (secreted by the edge of the mantle). </li></ul><ul><li>An thick calcareous middle layer, known as prismatic layer. </li></ul>
  8. 8. Digestive tract <ul><li>It is complex and complete. </li></ul><ul><li>The foregut region consist of an esophagus, stomach and mouth. </li></ul><ul><li>The mouth cavity is surrounded by toothed belt known as RADULA. </li></ul><ul><li>The pattern of the stomach varies according to the mollusks diet. </li></ul><ul><li>Radula is used for scrapping algae. </li></ul>
  9. 10. <ul><li>Is through the gills called CTENIDIA. (located in mantle cavity) </li></ul><ul><li>Excretion of waste through the metanephridia, gills and body. </li></ul><ul><li>But terrestrial species have lost their ctenidia and replaced by lungs that can function for both water and air. </li></ul><ul><li>These would vary from species to species. </li></ul>The Respiration and Excretion
  10. 11. The Circulatory and Nervous System <ul><li>Blood circulates through the gill filaments. </li></ul><ul><li>Most mollusk blood have a respiratory pigment known as HEMOCYANIN ( copper compound ). </li></ul><ul><li>The oxygenated blood is bluish in color, while deoxygenated blood is colorless. </li></ul>
  11. 12. <ul><li>Blood circulation would vary and it is mediated by a muscular heart. </li></ul><ul><li>It also possess well-developed sensory organs. The highest degree of development are found in CLASS CEPHALOPODA </li></ul>
  12. 13. Reproduction <ul><li>Reproduction is sexual. </li></ul><ul><li>The fertilized egg develops into a swimming form called TROCHOPHORE larva. </li></ul><ul><li>The larva stage is also present in the development of the annelids. </li></ul><ul><li>Then elongates to become a VELIGER LARVA. </li></ul>
  13. 14. Class Gastropoda <ul><li>From the Greek word “Gastro + poda” means stomach foot. </li></ul><ul><li>DEFINING CHARATERISTICS : </li></ul><ul><li>Visceral mass nervous systems become twisted 90 – 180 degrees (exhibiting torsion) </li></ul><ul><li>Proteinaceous shield on the foot. </li></ul>
  14. 15. (Class Gastropoda…….) <ul><li>Most of the approximately 40,000 living species of gastropods have shells. </li></ul><ul><li>However there are quite a few groups that have either reduced or internal shells, or no shell at all. </li></ul><ul><li>Shelled forms are generally called &quot; snails &quot; </li></ul>
  15. 16. <ul><li>Forms without shells are called &quot;slugs“ </li></ul><ul><li>However the terrestrial slugs are not closely related to the various marine forms that are without shells. </li></ul><ul><li>Although most Gastropods are marine, there are numerous forms in both freshwater and terrestrial environments </li></ul>
  16. 17. ANATOMY OF THE GASTROPOD WITH SHELL
  17. 18. Class Pelecypoda (Bivalva) <ul><li>The bivalves include forms such as clams , mussels , scallops , oysters , as well as many less familiar forms. </li></ul><ul><li>Most bivalves are ciliary feeders (or filter-feeders) </li></ul><ul><li>Bivalves are exclusively aquatic; </li></ul>
  18. 19. <ul><li>Bivalves are laterally compressed animals, with two shell &quot; valves &quot; that are hinged on the animal's dorsal surface. </li></ul><ul><li>The approximately 8,000 living species of bivalves are mostly marine, but there are many freshwater species as well (however, no terrestrial ones </li></ul>
  19. 20. Continue on Bivalva…… <ul><li>Bivalves are found in just about every marine environment, from the intertidal zone to the deepest marine habitats. </li></ul>Spondylus americanus Glycymeris glycymeris Felaniella vilardeboana
  20. 21. <ul><li>Most bivalves are suspension feeders, filtering small organisms and organic particles from the water (such as bacteria , phytoplankton , zooplankton , and nonliving organic detritus ). </li></ul>
  21. 23. after Brusca & Brusca 1990 Left Valve and Dorsal View of a Clam Shell
  22. 24. Bivalve continue… <ul><li>The shell is made up of three layers :  </li></ul><ul><li>The periostracum or thin outer layer that is made of horny, organic material called conchiolin , </li></ul>
  23. 25. <ul><li>the prismatic or thick middle layer that is made up of calcium carbonate crystals arranged in vertically, </li></ul><ul><li>and the nacerous or thinner inner layer that is composed of thin horizontally arranged calcium carbonate crystals </li></ul>
  24. 27. Bivalve continue…… <ul><li>Food entering the mouth is passed anteriorly to the stomach via ciliary action. </li></ul><ul><li>  The stomach is surrounded by a large digestive gland and is divided into two regions.  In the first region ( dorsal ) the esophagus and ducts of the digestive gland enter and it contains a ventral style sac. </li></ul>Food and nutrition:
  25. 28. <ul><li>This dorsal portion of the stomach is lined with chitin except for the large folded and ciliated sorting region, into which the digestive gland opens.  </li></ul><ul><li>At the apex of the stomach is a tooth-like projection called the gastric shield, which arises from the chitinous girdle .  At the end of this region is the cecum. </li></ul>
  26. 29. Members of the Class Bivalva A scallop Tridacna (Tridacna) gigas Pharella javanica
  27. 30. Class Cephalopoda <ul><li>Cephalopods , which include the familiar squids and octopus include species which are the largest known invertebrates (giant squid , up to 20 meters long, including tentacles), </li></ul><ul><li>The most intelligent, and the fastest swimming aquatic invertebrates ( squid ). </li></ul>
  28. 31. <ul><li>There are also forms with external shells ( nautilus ), and internal hard shells ( cuttlefish ). </li></ul><ul><li>Most of the approximately 650 living species of Cephalopods are active swimmers </li></ul>
  29. 32. (continue on Class Cephalopods……) <ul><li>Cephalopods have a closed circulatory system, an adaptation to their active lifestyle, as opposed to the open circulatory system found in other molluscs . </li></ul>
  30. 33. <ul><li>Squid in particular are often very abundant in pelagic marine environments, where they are voracious predators of many organisms, especially fish. </li></ul><ul><li>In return, they are also the major prey item of many fish and some marine mammal species. </li></ul>
  31. 34. Anatomy of the Cephalopods
  32. 35. Class Aplacophora <ul><li>250 living species (poorly studied!) of marine, wormlike, </li></ul><ul><li>bilaterally symmetrical </li></ul><ul><li>living at moderate, to very great depths, usually on or in soft bottoms.  </li></ul><ul><li>They have no shell, but have calcareous spicules in the body surface.  </li></ul>
  33. 36. <ul><li>The foot is restricted to an anterior pedal shield or to a narrow groove running the length of the body. </li></ul><ul><li>Aplacophorans have a radula and a posterior mantle cavity.  </li></ul><ul><li>Some are detritus feeders, others are predators.  </li></ul><ul><li>They range in length from 1 to 300 millimeters. </li></ul>
  34. 37. Summary <ul><li>Characteristics of Mollusca:- </li></ul><ul><li>Bilaterally symmetrical. </li></ul><ul><li>Body has more than two cell layers, tissues and organs. </li></ul>
  35. 38. <ul><li>Body without cavity. </li></ul><ul><li>Body possesses a through gut with mouth and anus. </li></ul><ul><li>Body monomeric and highly variable in form, may possess a dorsal or lateral shells of protein and clacareous spicules. </li></ul>
  36. 39. <ul><li>Has a nervous system with a circum-esophageal ring, ganglia and paired nerve chords. </li></ul><ul><li>Has a true closed circulatory system with a heart. </li></ul><ul><li>Has gaseous exchange organs called ctenidial gills. </li></ul>Continue……
  37. 40. <ul><li>Has a pair of kidneys. </li></ul><ul><li>Reproduction normally sexual and gonochoristic. </li></ul><ul><li>Feed a wide range of material. </li></ul><ul><li>Live in most environments </li></ul>
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