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Gastropods and Pelecypods

Gastropods and Pelecypods. How to make a living inside your shell. Phylum Mollusca. Ancient Group of Animals Second “largest” animal phylum Over 100,000 extant species described Marine, freshwater, terrestrial (flying is the only lifestyle mollusks haven’t accomplished)

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Gastropods and Pelecypods

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  1. Gastropods and Pelecypods How to make a living inside your shell

  2. Phylum Mollusca • Ancient Group of Animals • Second “largest” animal phylum • Over 100,000 extant species described • Marine, freshwater, terrestrial (flying is the only lifestyle mollusks haven’t accomplished) • Diversity of body forms

  3. Phylum Mollusca • Class Gastropoda

  4. Phylum Mollusca • Class Gastropoda

  5. Phylum Mollusca • Class Gastropoda

  6. Phylum Mollusca • Class Gastropoda • Class Bilvalvia (Pelecypoda)

  7. Phylum Mollusca • Class Gastropoda • Class Bilvalvia (Pelecypoda)

  8. Phylum Mollusca • Class Gastropoda • Class Bilvalvia (Pelecypoda)

  9. Phylum Mollusca • Class Gastropoda • Class Bivalvia • Class Cephalopoda

  10. Phylum Mollusca • Class Gastropoda • Class Bivalvia • Class Cephalopoda

  11. Phylum Mollusca • Class Gastropoda • Class Bivalvia • Class Cephalopoda

  12. Phylum Mollusca • Class Gastropoda • Class Bivalvia • Class Cephalopoda • Class Polyplacophora

  13. Phylum Mollusca • Class Gastropoda • Class Bivalvia • Class Cephalopoda • Class Polyplacophora • Class Monoplacophora

  14. Phylum Mollusca • Class Gastropoda • Class Bivalvia • Class Cephalopoda • Class Polyplacophora • Class Monoplacophora • Class Scaphopoda

  15. Phylum Mollusca • Class Gastropoda • Class Bivalvia • Class Cephalopoda • Class Polyplacophora • Class Monoplacophora • Class Scaphopoda • Class Aplacophora

  16. What makes a mollusc a mollusc?The molluscan “bauplan” • Body divided into three regions • Head (typically reduced) • Foot • Visceral mass

  17. What makes a mollusc a mollusc?The molluscan “bauplan” • Body divided into three regions • Head • Foot • Visceral mass • Body has a unique “organ” the mantle • Covers the dorsal portion of the animal • Is folded into a “skirt” to form a chamber that houses the gills, and openings for digestive, urinary, and reproductive systems • May have several functions • Secretes a calcareous shell in some forms (bivalves, most gastropods, some cephalopods, monoplacophora, polyplacophra)

  18. General Body Structure of a Mollusk

  19. What makes a mollusc a mollusc?The molluscan “bauplan” • Body divided into three regions • Head • Foot • Visceral mass • Body has a unique “organ” the mantle • Nervous system consists of a pharygeal ring and a two nerve chords • “Closed” circulatory system • Coelom is reduced (three sections, one surrounds the heart, one the nephridia and the other the gonads) • Bilateral symmetry (may be “lost” in adult forms) • Use cilia for movement (locomotion or to move water)

  20. What makes a mollusc a mollusc?The molluscan “bauplan” • Body divided into three regions • Head • Foot • Visceral mass • Body has a unique “organ” the mantle • Nervous system consists of a pharygeal ring and a two nerve chords • Open circulatory system • Coelom is reduced (three sections, one surrounds the heart, one the nephridia and the other the gonads) • Bilateral symmetry (may be “lost” in adult forms) • Use cilia for movement (locomotion or to move water)

  21. What makes a mollusc a mollusc?The molluscan “bauplan” • Body divided into three regions • Head • Foot • Visceral mass • Body has a unique “organ” the mantle • Nervous system consists of a pharygeal ring and a two nerve chords • “Closed” circulatory system • Coelom is reduced (three sections, one surrounds the heart, one the nephridia and the other the gonads) • Bilateral symmetry (may be “lost” in adult forms) • Use cilia for movement (locomotion or to move water)

  22. What makes a mollusc a mollusc?The molluscan “bauplan” • Body divided into three regions • Head • Foot • Visceral mass • Body has a unique “organ” the mantle • Nervous system consists of a pharygeal ring and a two nerve chords • “Closed” circulatory system • Coelom is reduced (three sections, one surrounds the heart, one the nephridia and the other the gonads) • Bilateral symmetry (may be “lost” in adult forms) • Use cilia for movement (locomotion or to move water)

  23. What makes a mollusc a mollusc?The molluscan “bauplan” • Body divided into three regions • Head • Foot • Visceral mass • Body has a unique “organ” the mantle • Nervous system consists of a pharygeal ring and a two nerve chords • “Closed” circulatory system • Coelom is reduced (three sections, one surrounds the heart, one the nephridia and the other the gonads) • Bilateral symmetry (may be “lost” in adult forms) • Use cilia for movement (locomotion or to move water)

  24. Gastropods – Introduction • Snails, slugs and others • The largest group of molluscs (over 40,000 recent species described) • Large foot used for locomotion (usually) • Posses a “radula” (used to scrape food in grazing snails, highly specialized in some groups) • Shell is coiled – result of “torsion” during larval development

  25. Gastropods – Introduction • Only mollusk group to have terrestrial forms • Many species have well developed eyes • Head often has tactile sensory appendages

  26. Gastropods – Introduction • Only mollusk group to have terrestrial forms • Many species have well developed eyes • Gas exchange via gills (most species) or highly vascularized mantle cavity or “lung” (pulmonate snails & some terrestrial operculate snails)

  27. Gastropods – general form

  28. Gastropods - Torsion

  29. Gastropods – The radula • Scraping tool used to feed • Common to all mollusks (except bivalves) • May be modified

  30. Cone snails – ocean predators • In cone snails, the radula has been modified into “darts.” • When the snail senses prey (such as the hapless fish, above) the proboscis shoots out and one poison filled dart harpoons the prey. • The poison is a neurotoxin, that immobilizes the prey • Cone snail venom may be fatal to humans

  31. Gastropod Video • Part 1 - http://www.youtube.com/watch?v=z6Z2XCdmEwU • Part 2 – http://www.youtube.com/watch?v=O0lLQLAvYFI&feature=related

  32. Bivalves - Introduction • Clams • Over 15,000 recent species • Mostly marine • Common inhabitant of deep sea thermal vents • Freshwater forms

  33. Bivalves - Introduction • Only mollusks to lack a radula • Classified based on gill structure • Reduced head • Laterally compressed • Hatchet-shaped foot • Adapted for burrowing

  34. Bivalves – Life History • First larval stage is a trochophore (common to all mollusks) • Morphs into veliger stage • Veliger morphs into juvenile (has same form as adult) • Juvenile grows by accretion at mantle margin

  35. Bivalves - Anatomy • Time to look at you “clam” • Northern quahog Venus mercenaria

  36. Bivalves - External • Two valves • Valves hinged on dorsal side • Notice the growth lines (concentric rings)

  37. Bivalves – Shell Morphology & Physiology • Most mollusks secrete a shell • Shell is composed of calcium carbonate (same material used by corals) • Protected by periostracum • Prismatic layer (crystals oriented vertically) • Nacreous layer (crystals oriented horizontally)

  38. Bivalves – Internal Anatomy & Physiology • Teeth – keep shells from slipping • Ligament – connective tissue that contracts when shell is opened • Adductor muscles – contract to allow the animal to “clam up” • Pallial line – attachment point for the mantle to the shell • Pallial sinus – shows position of the siphons

  39. Bivalves – Internal Anatomy & Physiology • Mantle – surrounds the body & apressed to the shell • Contains sensory organs (tactile tentacle, light sensing eye spots • Secretes the shell • Is fused (two halves joined) dorsally, open ventrally • May be modified to form siphons

  40. Bivalves – Anatomy & Physiology (Under the mantle) • Foot • Primary form of locomotion • Animal pushes foot into substrate • Foot is filled with blood, causing it to expand and grip substrate • Clam pulls body toward foot

  41. Bivalves – Anatomy & Physiology (Under the mantle) • Gills (ctenidia) • Respiratory function • Secondary function is to filter water to capture food • Gill structure is used to classify bivalves

  42. Bivalve gill evolution • Protobranchs (primitive)

  43. Protobranchs (primitive) Filibranchs Gills fold back to form a “U”-shaped structure. Mantle cavity divided by gills into a ventral inhalent chamber and a dorsal exhalent chamber. Chambers connect to outside via siphons Gills filter food from the water passing across them. Cilia move water across the gills. Bivalve gill evolution

  44. Bivalve gill evolution • Protobranchs (primitive) • Filibranchs • Eulamellibranchs

  45. Bivalve gill evolution • Protobranchs (primitive) • Filibranchs • Eulamellibranchs • Septibranchia

  46. Bivalves – Anatomy & Physiology (Under the mantle) • Digestive System • Labial palps surround oral opening • Short esophagus • Stomach • Crystalline style

  47. Bivalves – Anatomy & Physiology (Under the mantle) • The style – found in many mollusks • Serves several functions • “windlass” to pull food string from esophagus to stomach • Stirring rod • Source of digestive enzymes

  48. Bivalves – Anatomy & Physiology (Under the mantle) • Digestive System • Labial palps surround oral opening • Short esophagus • Stomach • Crystalline style • Intestine (loops around stomach) • Rectum

  49. Bivalves – Anatomy & Physiology (Under the mantle) • Circulatory System • Pericardium encloses the heart • Heart has two auricles and one ventricle • Circulatory system is open (blood passes from arteries into sinuses in the tissue and then back into veins). • Most clams have haemocyanin as the blood pigment. Some have haemoglobin.

  50. Bivalves – Anatomy & Physiology (Under the mantle) • Urogenital System • Posses two nephridia (similar to kidneys) • Most bivalves are dioecious • Gonads are usually adjacent to the intestine • Gonads and nephridia discharge to the posterior portion of the mantle cavity

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