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Phylum Mollusca. Molluscan Characteristics. Large range in size 1 cm long to 18 m All mollusks… 2 Body Parts- head-foot and visceral mass Mantle that secretes a calcareous shell (made of calcium carbonate) and covers the visceral mass. Molluscan Characteristics Continued. All mollusks…

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molluscan characteristics
Molluscan Characteristics
  • Large range in size
    • 1 cm long to 18 m
  • All mollusks…
    • 2 Body Parts- head-foot and visceral mass
    • Mantle that secretes a calcareous shell (made of calcium carbonate) and covers the visceral mass
molluscan characteristics continued
Molluscan Characteristics Continued
  • All mollusks…
    • Mantle cavity functions in
      • Excretion
      • Gas exchange
      • Elimination of digestive wastes
      • Release of reproductive products
    • Bilateral symmetry
    • Coelom reduced to cavities surrounding the heart, nephridia, and gonads
molluscan characteristics continued1
Molluscan Characteristics Continued
  • All mollusks…
    • Trocophore larvae (aquatic with cilia)
    • Open circulatory system in all but one class (Cephalopoda)
    • Radula usually present and used in scraping food
molluscan vocabulary
Molluscan Vocabulary
  • Head-foot:
    • Anterior head- contains mouth and sensory structures
    • Elongated foot- used for attachment and locomotion
  • Visceral Mass:
    • Contains organs for digestion, circulation, reproduction, and excretion
    • Dorsal to head-foot
molluscan vocabulary1
Molluscan Vocabulary
  • Mantle:
    • Attaches to visceral mass
    • May secrete a shell
  • Mantle Cavity:
    • Opens to the outside
    • Functions in gas exchange, excretion, elimination of digestive wastes, and release of reproductive products
molluscan vocabulary2
Molluscan Vocabulary
  • Radula:
    • Functions in scraping food (teeth and tongue in one structure)
    • Rows of posteriorly curved teeth
class gastropoda
Class Gastropoda

Snail

  • Snails, limpets, and slugs
  • 35,000 living species
  • Largest and most diverse molluscan class
  • Used for food (escargot)
  • Intermediate hosts for some human parasites
  • Means “stomach foot”

Slug

Limpet

class gastropoda1
Class Gastropoda
  • Torsion:
    • 180⁰ counterclockwise twisting of the visceral mass, mantle, and mantle cavity
    • Allows the head to enter the shell first- protects against predators
    • Operculum (covering on the foot)- prevents the snail from drying out
class gastropoda2
Class Gastropoda
  • Coiled shells- assymetrical
  • Locomotion- ciliated, flattened foot
  • Feeding:
    • May scrape organisms (ex. Algae) using radula
    • May eat plants, dead organisms, parasites, or predators
class gastropoda3
Class Gastropoda
  • Gas exchange:
    • Occurs with the mantle
    • Modern gastropods have one gill (compared to 2 in ancestors)
    • Siphon- inhalant tube that is a rolled extension of the mantle
  • Open circulatory system
  • Hydraulic skeleton- fluid supports body structure
class gastropoda4
Class Gastropoda
  • Reproduction:
    • Marine snails
      • Dioecious
      • External fertilization
    • Land snails
      • Monoecious
      • Internal fertilization
    • Eggs hatch into free-swimming trochophore larva
class bivalvia
Class Bivalvia

NB #97

  • 30,000 species
    • 2nd largest molluscan class
  • Clams, oysters, mussels, and scallops
  • Sheet-like mantle & shell
    • 2 valves
  • Edible
  • May form pearls
  • Filter feeders
    • Remove bacteria from the water
  • Conchology- study of mollusk shells
class bivalvia1
Class Bivalvia
  • Structures:
    • 2 convex shell halves- called valves
    • Hinge along shell made of protein
    • Teeth-
      • Tongue & groove modifications that prevents the valves from twisting
    • Umbo:
      • Oldest part of the shell
      • Swollen area near the shell’s anterior margin
class bivalvia2
Class Bivalvia
  • Structures:
    • Shell forms as a single structure (although it looks like two)
    • Hinge- elastic due to more protein and less calcium carbonate (allows the shell to open when certain muscles relax)
    • Adductor muscles- strong muscles that close the shell (makes it difficult to pry a shell open)
class bivalvia3
Class Bivalvia
  • Pearls
    • Mantle attaches to the shell around the adductor muscles
    • If one grain of sand lodges between the shell and the mantle, the mantle secretes nacre around the irritant (which may also be a parasite)
      • This process eventually forms a pearl
      • Nacre is also referred to as “Mother-of-Pearl”
      • Process takes approximately two years
class bivalvia4
Class Bivalvia
  • Processes
    • Gas exchange
      • Gills form folded sheets (lamellae)
        • One end attached to the foot and the other end attached to the mantle
      • Cilia move water into the gills
    • Digestion
      • The gills also trap food particles
      • Cilia move food particles from the gills through ciliated food grooves
      • Considered filter feeders
class bivalvia5
Class Bivalvia
  • Filter feeding
    • Valuable process for the environment
    • Average oyster filters approximately 6 liters of water an hour
    • Pollution, harvesting, and environmental changes have reduced bivalve numbers in certain areas
class bivalvia6
Class Bivalvia
  • Open circulatory system
  • Nervous system
    • 3 pairs of interconnected ganglia
    • Some species (ex. Scallops) develop photoreceptors as complex eyes with a lens and a cornea

Eyes

class bivalvia7
Class Bivalvia
  • Reproduction
    • Most are dioecious
    • Few are moneocious
    • Some are protandric (male early and then develop into a female)
    • Usually reproduce externally
class bivalvia8
Class Bivalvia
  • Habitat and Diversity
    • Aquatic (either marine or freshwater)
    • May bury themselves, attaches to substrates, or bore in materials (ex. Wood)
    • The foot secretes strands that cement the animal to it’s location
class cephalopoda
Class Cephalopoda
  • Cephalopod- “head-foot”
  • Octopuses, squid, cuttlefish, and nautiluses
  • Most complex mollusks (actually most complex invertebrate)
  • Anterior foot modified into tentacles to capture prey
class cephalopoda1
Class Cephalopoda
  • Shell
    • The only living cephalopod with an external shell is the nautilus
      • As it grows, the nautilus secretes a new shell and leaves the empty shell behind
    • An internal shell is present in the cuttlefish
      • Has gas-filled spaces that increase buoyancy
      • The shell (called a cuttlebone) is used to make powder for polishing or feed pet birds
class cephalopoda2
Class Cephalopoda
  • Locomotion
    • Move with a jet-propulsion system
      • Force water out of the mantle cavity in a funnel
      • Muscles on the funnel control the direction of movement
    • Squids have posterior fins for stability
      • May swim as fast as 30 km/hr
    • Crawl around using tentacles
class cephalopoda3
Class Cephalopoda
  • Feeding & Digestion
    • Locate prey by sight
    • Capture prey with tentacles
      • Tentacles are made of protein- occasionally have a hook
    • Beak- jaws used to tear food
    • Cuttlefish & nautiluses- eat small invertebrates
    • Octopuses- nocturnal & eat snails, fishes, & crustaceans (inject venom)
    • Squid- fishes & shrimp
class cephalopoda4
Class Cephalopoda
  • Closed circulatory system
  • Eyes similar to vertebrate eyes
  • Ink gland located behind the anus
    • Ink contains melanin
    • Black or brown in color
  • Octopus Video
class cephalopoda5
Class Cephalopoda
  • Nervous system
    • Complex lobes
    • 20th Century experiments demonstrated that cephalopods may be trained to attack, kill, and feed when stimulated
    • May navigate mazes
    • Can remember information for up to four months
class cephalopoda6
Class Cephalopoda
  • Reproduction
    • Dioecious
    • Males encase sperm in spermatophores
      • One male tentacle (hectocotylus) is modified for spermatophore transfer
    • Male and female tentacles intertwine during copulation
      • Male inserts hectocotylus into female mantle cavity and releases the spermatophore
    • Females release eggs
      • Hatchlings resemble the adults
      • Adults do not care for the young
other mollusks
Other Mollusks

Chiton

  • Class Polyplacophora
    • Chitons
    • Shell that divides into eight valves
  • Class Scaphopoda
    • Tooth shells or tusk shells
    • At least 300 species
    • Shell is open at both ends
  • Class Monoplacophora
    • Thought extinct until 1952
  • Class Aplacophora
    • Lack shells

Tusk shell

Monoplacophora

Aplacophora