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Phylum Mollusca

Phylum Mollusca. Phylum Mollusca (mollis, soft). Body usually an anterior head, ventral foot and a dorsal visceral mass . Covered by a fleshy outgrowth of the body wall called a mantle . Shell if present is secreted by the mantle

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Phylum Mollusca

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  1. Phylum Mollusca

  2. Phylum Mollusca (mollis, soft) • Body usually an anterior head, ventral foot and a dorsal visceral mass. • Covered by a fleshy outgrowth of the body wall called a mantle. • Shell if present is secreted by the mantle • Radula- a tongue-like structure bearing transvers rows of minute chitinous teeth. • Good phylum for demonstrating Adaptative Radiation. • With the exception of Monoplacophora, the phylum is unsegmented.

  3. Systems • Skeletal- Mantle may secretes a shell. Use hydrostatic pressure for ventral muscular foot. • Muscles -Ventral muscular foot and other muscles present. • Digestive- complete complex with salivary glands, digestive gland and Rasping tongue (Radula). • Circulatory - Open except for Cephalopoda. Dorsal heart, usually in a pericardial cavity. • Respiratory - Ctenidia (gills) in mantle cavity, respiratory pigment is copper.

  4. Systems • Excretory- by nephridia usually connecting to the pericardial cavity, • the coelom is usually reduced to the cavities of the nephridia, gonads and pericardium. • Nervous - Nerve ring with various pairs of ganglia—two pairs of nerve cords, one innervating the foot, the other the visceral mass (modified ventral ladder-like system) • Integumentary - Mantle • Endocrine - nervous systems produces hormones. • Reproductive - varied- monoecious, protandric, or dioecious. Larva in marine = trochophore and veliger, in freshwater clam is glochidium.

  5. Taxonomy Mouse click on any underlined taxon to go to information of that taxon • Classes: • Monoplacophora (no specimens) • Polyplacophora • Scaphopoda • Gastropoda • Bivalvia • Cephalopoda

  6. Back to Taxonomy Class Polyplacophora (Chitons) • Elliptical body with dorsal surface bearing eight overlapping limy plates (valves) • Chitons are marine. • They live mostly in shallow water. • All are similar in morphology and ecology. • They are slow moving microphagous feeders, scraping algae and other small invertebrates from substrate with their radula. • Genera • Katherina • Cryptochiton

  7. Return to Polyplacophora Polyplacophora representative genera. • Katherina Katherina dorsal surface Katherina ventral surface

  8. Return to Polyplacophora Polyplacophora representative genera. • Cryptochiton Cryptochiton dorsal surface Cryptochiton ventral surface

  9. Class Scaphopoda Back to Taxonomy • Tooth shells (or Tusk shells) • Shell and mantle slender, tubular, and slightly curved. It is open at both ends Dentalium

  10. Class: Gastropoda Return to Taxonomy • Univalves, Shell usually spiral, distinct head, scraping radula. • Visceral mass typically turned 180° counterclockwise = torsion. And the visceral mass is coiled in shell. • Representatives • Garden snail (Helix), Whelks (Busycon),Conch, Cowries,, Sea hare, Nudibranchs, Slugs, and abalone.

  11. Helix (garden snail) Helix, ventral view Helix, dorsal view Return to Gastropoda Helix, side view

  12. Busycon (Whelk) Return to Gastropoda Busycon (shell removed) Busycon shells Busycon eggs

  13. Return to Gastropoda Other Gastropods Abalone shells Conch Examples of gastropoda

  14. Return to Gastropoda Other Gastropods (continues) Sea Hair side view Sea Hair (ventral view) Slug

  15. Return to Taxonomy Class Bivalvia • Shell of two lateral valves, with dorsal hinge. • Mantle of flattened right and left lobes. Posterior margin commonly forming siphons • Labial palps beside mouth • No head • No radula Representative bivalves

  16. Return to Bivalvia Representatives of Bivalvia • Anadonta(Freshwater clam) • Teredo (Shipworm) • Rock boring clam • Ostrea (Oyster) • Pecten (Scallop) • Freshwater clamdissection

  17. Return to Representatives Anadonta Dissection

  18. Return to Representatives Teredo (shipworm)and the Rock boring worm Teredo Teredo in wood Rock boring clam

  19. Return to Representatives Oyster and Scallop Scallop shells Oyster cluster Oyster shells

  20. Return to Representatives Freshwater Clam Dissection • External shell • Mantle • One mantle flap removed. • Visceral Mass (not dissected) • Dissected Visceral Mass I • Dissected Visceral Mass II • Dorsal Heart • Dorsal heart I(showing auricle or atrium) • Dorsal heart II(showing ventricle) • Dorsal heart III (ventricle) • Internal shell (showing muscle scars and pallial line)

  21. Return to contents External Shell

  22. Return to contents Mantle

  23. Return to contents One side of mantle removed

  24. Return to contents Visceral Mass

  25. Return to contents Dissected Visceral Mass (I)

  26. Return to contents Dissected Visceral mass (II)

  27. Return to contents Dorsal Heart I

  28. Return to Contents Dorsal Heart II

  29. Return to contents Dorsal Heart III

  30. Return to contents Pallial line Internal parts of shell Shell

  31. Return to Taxonomy Class Cephalopoda • Large head with conspicuous eyes • Ventral foot modified into tentacles(are arms) with suckers. • Representative Cephalopods • Nautilus(Chambered Nautilus) • Octopus(Octopus) • Loligo(Squid) • Sepia(Cuttle fish)

  32. Return to Cephalopoda Nautilus • (South Pacific and Indian Ocean)

  33. Return to Cephalopoda Octopus • Eight arms

  34. Return to Cephalopoda Loligo Internal skeleton = Pen

  35. Return to Cephalopoda Sepia • Cuttlebone (internal skeleton)

  36. Return to Taxonomy Class Monoplacophora • First 10 specimens of Neopilina were taken in 1952 from dark muddy clay at 3350 m(11,000 ft) off the coast of Costa Rica. • Since then other species have been found in Indo-Pacific and South Atlantic Oceans. • Neopilina is the only living genus • Neopilina has segmented muscles

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