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Phylum Mollusca. Ch. 12. General Ideas Phylum Mollusca. Members are called Mollusks Example Species: Slug Squid Scallops Octopus Snails. Phylum Mollusca Characteristics. Over 100,000 Species Many are marine, some are freshwater, and some live in moist land environments

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general ideas phylum mollusca
General IdeasPhylum Mollusca
  • Members are called Mollusks
  • Example Species:
    • Slug
    • Squid
    • Scallops
    • Octopus
    • Snails
phylum mollusca characteristics
Phylum Mollusca Characteristics
  • Over 100,000 Species
  • Many are marine, some are freshwater, and some live in moist land environments
  • Body in two parts:
    • Head-foot
    • Visceral mass
  • Bilateral Symmetry
  • Radula (for feeding)
  • Mantle that secretes a calcareous shell
  • Small coelom for heart, nephridia, and gonads
  • Trochophore larvae produced (Protostome characteristics)
  • Open circulatory system in all except cephalopods
  • May have been the first animals in the course of evolution to have a coelom
important mollusk body parts
Important Mollusk Body Parts
  • Look at the Picture on Page 182
  • Mantle
    • Attaches to the visceral mass, enfolds most of the body, and may secrete a shell that overlies the mantle
  • Radula
    • Tongue-like organ with rows of teeth found in the mouth used to scrape food into their mouths
  • Mantle Cavity
    • Found between the mantle and the foot
    • Room for organs
    • Gas exchange
    • Excretion
    • Elimination of wastes
    • Release of gametes (reproduction)
feeding and digestion
Feeding and Digestion
  • Mollusks have complete guts with digestive glands, stomachs, and intestines.
  • The digestive system has 2 openings-a mouth and an anus.
  • Radula
    • Can be used to scrape algae, drill holes in shells, or tear up the food the capture
    • Few mollusks do not have radulas, such as clams who are filter feeders.
respiration
Respiration
  • Most mollusks have respiratory structures called gills
    • Gills are parts of the mantle that consist of a system of projections like fringes of a blanket.
    • Gills contain a rich supply of blood for the transport of oxygen to the blood and for the removal of carbon dioxide from the blood.
    • Gills also move water into and through the mantle cavity in a continuous stream using highly branched structures that increase surface area through which gases can diffuse.
circulation mollusks have a well developed circulatory system that even includes a chambered heart
CirculationMollusks have a well-developed circulatory system that even includes a chambered heart.

Open Circulatory System

Closed Circulatory System

Only some mollusks, such as squid.

Blood is confined to blood vessels as it moves through the body.

Mollusks that move quickly, such as octopi, need more energy than slow-moving mollusks, and the closed circulatory system quickly deliver nutrients and oxygen.

  • Most mollusks
  • Blood is pumped out of vessels into open spaces surrounding body organs
  • Enables animals to diffuse oxygen and nutrients into tissues that are bathed in blood and also to move CO2 from tissues into the blood.
  • Slow-moving mollusks, such as snails and clams, utilize this system because they do not need rapid delivery of oxygen and nutrients for quick movement!
excretion response to stimuli
Excretion & Response to Stimuli
  • Excretion:
    • Most mollusks get rid of metabolic wastes through nephridia (similar to annelida)
  • Response to Stimuli:
    • Have a nervous system that coordinates movement and behavior.
    • Mollusks that are more highly evolved, such as octopuses, have a brain. In addition, octopuses have complex eyes similar to human eyes with irises, pupils, and retinas. BUT, most mollusks only have simple structures in the eyes that reflect light.
movement
Movement
  • Mollusks can move many different ways:
    • Muscular foot of a clam enables it to burrow into wet sand
    • Mollusks with 2 shells can clap their shells together for short bursts of rapid swimming.
    • Most slugs and snails creep along moist areas on a slime trail of mucus secreted by glands in the foot.
    • Octopi and squid take water into the mantle cavity and expel it through a tube called a siphon.
reproduction
Reproduction
  • Mollusks generally reproduce sexually by releasing their eggs and sperm into the water at the same time where fertilization occurs externally….but there are a few exceptions:
    • A few bivalves and gastropods that live on land are hermaphrodites and fertilization occurs internally.
    • Copulation can occur through mutual sperm transfer (think annelid) or even where one is male and one is female (more rare)
taxonomy of mollusca
Taxonomy of Mollusca
  • Kingdom Animalia
    • Phylum Mollusca
      • Class Caudofoveata
      • Class Aplacophora
      • Class Polyplacophora
      • Class Monoplacophora
      • Class Scaphopoda
      • Class Bivalvia
      • Class Gastropoda
      • Class Cephalopoda
class bivalvia
Class Bivalvia
  • 30,000 species (2nd larges molluscan class)
  • Filter-feeders (also remove bacteria from polluted water) DO NOT EAT BIVALVES FROM POLLUTED WATER!
  • No head or radula, but do have wedge-shaped foot
  • Marine and Freshwater
  • Two shells called valves
  • Umbo – oldest part of the shell
  • Example species: Clams, oysters, mussels, & scallops
slide17

"There once was an oysterWhose story I tell,Who found that some sandHad got into his shell.It was only a grain,but it gave him great pain.For oysters have feelingsAlthough they're so plain.Now, did he beratethe harsh workings of fateThat had brought himTo such a deplorable state?Did he curse at the government,Cry for election,And claim that the sea shouldHave given him protection?'No,' he said to himselfAs he lay on a shell,Since I cannot remove it,I shall try to improve it.

Now the years have rolled around,As the years always do,And he came to his ultimateDestiny - stew.And the small grain of sandThat had bothered him soWas a beautiful pearlAll richly aglow.Now the tale has a moral,for isn't it grandWhat an oyster can doWith a morsel of sand?What couldn't we doIf we'd only beginWith some of the thingsThat get under our skin.” - Unknown

read write talk
Read, Write, Talk
  • Pick up the “Pearls” article and read it
  • Write on your paper interesting facts or something you do not understand
  • Last we will discuss, expect me to ask you questions!
slide31

Zebra Mussel Map:

http://fl.biology.usgs.gov/Nonindigenous_Species/ZM_Progression/zm_progression.html

zebra mussel 3 2 1
Zebra Mussel 3, 2, 1
  • Read
  • Write:
    • 3 most important facts
    • 2 questions you have
    • 1 connection (something you already know)
class gastropoda
Class Gastropoda
  • Marine, freshwater, & terrestrial
  • Over 35,000 species
  • Shell if present is coiled
  • Torsion – 180o counterclockwise twisting of viseral mass, mantle, & mantle cavity
  • One broad foot for creeping
  • Uses a Radula (rough tongue) to eat
  • 1 Shell (except nudibranchs and slugs)
  • Definite Head, Eyes and Tentacles
  • Example species:
    • Snails, Limpets, Slugs, Nudibranches
class polyplacophora
Class Polyplacophora
  • Chitons!
  • Have a reduced head, a flattened foot, and a shell that divides into 8 overlapping shell plates!
  • Most live near edge of marine waters (intertidal zone) and feed on algae
  • About 1,000 species
class cephalopoda
Class Cephalopoda
  • Foot modified into a circle of tentacles and a siphon
  • Most complex mollusks (and possible invertebrates)!
  • Shell reduced or absent
  • Marine
  • Well developed head and brain
  • Human-like eyes
  • Uses a beak, a radula,

and tentacles to eat

  • Less than 1,000 species
  • Well defined head
  • Example Species:
    • Octopuses, squid, cuttlefish, and nautiluses