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Phylum Mollusca Ch 12 – Molluscan Success. Mollusks are second only to arthropods in numbers of living species. Phylum Mollusca . Mollusca = “Soft Bodied” (Latin). ~555 Million Years Ago. Molluscan Characteristics. Range in size and body shape

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phylum mollusca ch 12 molluscan success

Phylum MolluscaCh 12 – Molluscan Success

Mollusks are second only to arthropods in numbers of living species

phylum mollusca
Phylum Mollusca
  • Mollusca = “Soft Bodied” (Latin)
molluscan characteristics
Molluscan Characteristics
  • Range in size and body shape
    • Largest  1000 lbs, 18m long (giant squid)
    • 80% less than 5 cm
molluscan characteristics1
Molluscan Characteristics
  • Body of three regions: head-foot, visceral mass, and mantle
  • Mantle cavity functions in excretion, gas exchange and reproduction
  • Bilateral symmetry
  • Protostome development
  • True coelomates (eucoelomates), reduced size
  • Open circulatory system in all but cephalopods
  • Radula present and used for scraping food
mollusk body
Mollusk Body
  • Three main regions
    • 1. Head-foot
      • Head (nervous structures) and foot (locomotion)
    • 2. Visceral Mass
      • Contain organs
    • 3. Mantle
mollusk body1
Mollusk Body
  • Mantle
    • Usually attaches to the visceral mass and enfolds most of the body. May secrete the shell.
  • Mantle Cavity
    • Between the mantle and foot. Opens to the outside and functions in gas exchange, excretion and reproduction.
  • Radula
    • A rasping structure found in the mouth. “Toothed tongue”
class gastropoda
Class Gastropoda
  • “Stomach foot”
  • Largest and most varied class of mollusks
  • ~35,000 living species
  • Examples: snails, slugs, conch, and limpets
  • Marine, freshwater, and terrestrial habitats
class gastropoda1
Class Gastropoda
  • Most have shells – calcium carbonate
  • Torsion - 180° twisting of the visceral mass, mantle, and mantle cavity. Used to bring head into shell.
  • Operculum closes shell opening.
  • Shell coiling: whorl, apex
  • Flattened foot for locomotion
    • Cilia
    • Muscular contractions
  • Use radula for scraping foot
class gastropoda2
Class Gastropoda

Maintenance Functions

  • Gas exchange occurs in mantle cavity
  • Open circulatory system
  • 3 chambered heart
  • Hydraulic skeleton – fluid under pressure in body
  • Some dioecious, some monoecious
world s weirdest gastropods
World’s Weirdest Gastropods
  • http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/weirdest-cone-snail/
  • http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/deadliest-zombie-snails/
  • http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/weirdest-sea-hare/
class bivalvia
Class Bivalvia
  • “Two valves”
  • Second largest molluscanclass: ~30,000 species
  • Includes clams, oysters, mussels, and scallops
  • Many edible, some form pearls
bivalve characteristics
Bivalve Characteristics
  • Marine and freshwater
  • No head or radula
  • Most are filter feeders
  • Adductor muscles used for defense
  • Mantle attaches to shell around adductor muscles
  • Pearl forms when sand lands between mantle & adductor
bivalve characteristics1
Bivalve Characteristics
  • Foot projects from front end of animal, through the valves
  • Foot used for burrowing
  • Siphon – “neck” used for intake of water and food and release of waste.
  • Complete digestive tract
  • Reduced nervous system
bivalve shell and shell structures
Bivalve Shell and Shell Structures
  • Two convex halves of the shell – valves
  • Umbo – oldest part of shell near anterior end
class bivalvia1
Class Bivalvia

Maintenance Function

Reproduction

  • Cilia covered gills
  • Cillia move water in and out of mantle
    • Incurrent Pore
    • Excurrent Pore
  • Gills in mantle cavity for gas exchange
  • Food trapping – cilia move food toward mouth
  • Most are dioecious, some monoecious
  • Gonads in visceral mass
  • External fertilization (most)
  • Trocophore larvae
beautiful bivalves
Beautiful Bivalves
  • http://video.nationalgeographic.com/video/animals/invertebrates-animals/other-invertebrates/weirdest-clam-vs-world/
  • https://www.youtube.com/watch?v=Z-32RfYNbOY
class cephalopoda
Class Cephalopoda
  • “Head Foot”
  • Includes octopuses, squid, cuttlefish, and nautiluses
  • Most complex mollusks/invertebrates
  • Foot modified into a circle of tentacles and a siphon
  • Shell reduced or absent in most
  • Head in line with elongate visceral mass
cephalapod shell
Cephalapod Shell
  • Shell reduced or absent in all but nautilus
  • Cuttlefish
    • Shell is internal. Cuttlebone is used to make polishing powder and bird treats (for calcium)
  • Squid
    • Pen: internal, chitinous structure
    • Cartilaginous plates in mantle wall, head, neck
  • Octopus
    • Absent
class cephalopoda1
Class Cephalopoda

Locomotion

Maintenance Functions

  • Predators
  • Jet-propulsion system
    • Muscle contractions
    • Forces water out through narrow funnel
  • Cuttlefish and squid very motile
  • Octopus more sedentary
  • Adhesive cups used for capture.
  • Beaklike jaws and radula
  • Complete digestive tract
  • Closed circulatory system
  • Complex nervous system
    • Brain and Eye
  • Chromatophores for defense (color change)
  • Discharge of ink
cephalopod reproduction
Cephalopod Reproduction
  • Cephalopods are dioecious
  • One tentacle of male is modified for spermatophore transfer
  • Tentacles intertwine during copulation. Spermatophores burst open and eggs are released through the oviduct.
  • Fertilized eggs attach to substrate
world s weirdest cephalopods
World’s Weirdest Cephalopods
  • http://video.nationalgeographic.com/video/animals/invertebrates-animals/octopus-and-squid/deadliest-cuttlefish-camouflage/
  • http://video.nationalgeographic.com/video/animals/invertebrates-animals/octopus-and-squid/octopus-vs-octopus-predation/
  • http://dsc.discovery.com/tv-shows/other-shows/videos/is-it-possible-vampire-squid.htm
class polyplacophora
Class Polyplacophora
  • “many plates”
  • Chitons
  • Shallow marine waters
  • Reduced head, flattened foot
  • Shell dives into eight dorsal valves
  • Crawl similar to gastropods
  • http://www.youtube.com/watch?v=r1iEU2Kx7MI
class scaphopoda
Class Scaphopoda
  • “Boat foot”
  • Tooth shells or Tusk shells
  • Burrowing marine animals
  • Conical shell that is open at both ends
  • Head and foot project from wider end
class monoplacophora
Class Monoplacophora
  • “One plate”
  • Undivided, arched shell
  • Broad, flat foot
  • Repeated pairs of gills and foot-retractor muscles
  • Thought to be extinct until 1952
class aplacophora
Class Aplacophora
  • “Without plate”
  • Lack a shell and crawl on ventral surface
  • Body and nervous system similar to flatworms
  • Most are surface dwellers on corals