Phylum Mollusca

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Phylum Mollusca
BY Ashley, Sam, Kelly, Jen, Adam November 14,
2007
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Origin

• The name Mollusca came from the Latin word
  mollis which means soft.

• Almost all Molluscas live in the sea

• The word Mollusca was first used by a french
  zoologist in 1798.

• The phylum Mollusca are one of the three most
  successful groups in the animal kingdom.

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General Characteristics

• There are over 160,000 species in this group.

• The body has three main parts a muscular foot
  usually used for movement a visceral mass
  containing most of the internal organs and a
  mantle, a fold of tissue that drapes over the
  visceral mass and secretes a shell.

• Soft bodied animals, most are protected by a
  hard shell made of calcium carbonate.

• Slugs, squids, and octopuses have a reduced
  internal shell or have lost their shell
  completely during their evolutions.

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• Has a true closed circulatory system with a
  heart and a pair of kidneys.

• Body has more than two cell layers, tissues and
  organs.

• Has a nervous system with a circum-esophageal
  ring, ganglia and paired nerve chords.

• Feed a wide range of material and live in most
  environments .

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• There are Eight different classes in Phylum
  Mollusca

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Uncommon
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• Aplacophora

Caudofoveata
Scaphopoda
Monoplacophora
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Common
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Cephalpoda
Polyplacophora

• Gastropoda

Bivalves
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Polyplacophora (chitons)

• Chitons have an oval-shaped body and a shell
  divided into eight dorsal plates.

• The body itself, is unsegmented.

• During low tide you can find there marine
  animals clinging to rocks along the shore.

• Chitons use their radula to cut and ingest algae.

• They have no head and use their foot for
  locomotion.

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Bivalvia (Clams, Mussels)

• Includes many species of clams, oysters, muscles,
  and scallops.

• Bivalves have a shell divided into two halves.

• The halves are hinged at the middorsal line, to
  protect their soft body they use their strong
  adductor muscles.

• They have no distinct head, and the radula has
  been lost.

• Some bivalves have eyes and sensory tentacles
  along the outer edge of the mantle.

• They feed by siphoning and filtering large
  particles from water.

• They can dig themselves into the sand very
  quickly to escape predators

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Gastropods (Snails, Slugs)

• About three-quarters of all living species are
  gastropods.

• Most gastropods are marine, But there are also
  many freshwater species, snails and slugs are
  among the gastropods that have adapted to land.

• The most distinctive characteristic of the
  class Gastropod is a developmental process known
  as torsion.

• Most have a single, spiraled shell into which
  the animal can retreat when threatened.

• Gastropods move literally at a snails pace by
  a rippling motion of their foot or by cilia.

• Most Gastropods use their radula to graze on
  algae or plants.

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Cephalopoda (squids, octopuses)

• Cephalopods use their tentacles to capture food.
  Then they use their beak like jaws to inject an
  immobilizing poison.

• There are around 786 distinct living species of
  Cephalopods.

• Cephalopods are found in all the oceans , at
  all depths. None of them can tolerate freshwater.

• Cephalopods are widely known as the most
  intelligent of the invertebrates, and have well
  developed senses and large brains larger than
  the brains of gastropods or bivalves.

• Cephalopods move usually by jet propulsion, a
  very energy-consuming way to travel compared to
  the tail propulsion used by fish.

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Works Cited

• Images form Google Images.
• http//www.earthlife.net/inverts/mollusca.html
• http//en.wikipedia.org/wiki/Cephalopoda
• http//www.meer.org/M30.htm
• http//www-biol.paisley.ac.uk/Courses/Tatner/biome
  dia/units/moll1.htm
• Google Images
• http//en.wikipedia.org/wiki/Bivalvia
• Cambells Biology Text