Phylum Mollusca

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Phylum Mollusca
Soft-bodied animals!
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3 Classes of Molluscs
GASTROPODA includes limpets, snails, slugs
and whelks BIVALVIA includes clams, oysters,
mussels, scallops and shipworms CEPHALOPODA
includes octopi, squid, cuttlefish, and nautilus
Above Limpet
Above Scallop showing off its eyes! Left
Cuttlefish and squid
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All forms of Molluscs have a body with three
parts

• Visceral Mass
• - The soft bodied portion that contains the
  internal organs
• Foot
• - A strong, muscular portion used for moving
  (or tentacles in cephalopods)
• Mantle
• A covering that goes around the visceral mass
• Can secrete a shell

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Find the Foot, Visceral Mass and Mantle!
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A diverse phylum

• Mollusca contains 80,000 different species
• Symmetry Bilateral
• Level of Organization Organ
• They also have a well developed nervous system, a
  circulatory system, and a brain.
• Cephalopods have a closed circulatory system
  (e.g. squid, octopus)
• Bivalves and Gastropods have an open circulatory
  system (e.g. clams, snails)

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• Feeding
• Complete digestive tract
• Most have a radula a sharp tongue like a nail
  file that they use to rasp at food
• Feeding strategies differ between the classes
• Excretion
• Complete excretory system with an anus
• Simple kidneys
• Reproduction
• Sexual with internal fertilization
• Most have separate sexes, although snails are
  usually hermaphroditic

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Class Bivalvia

• Two valves (shells), e.g. mussels, clams, oysters
• They have a muscular foot for digging
• They often attach to the substrate with byssal
  threads that hold them in place
• Some, like scallops, can swim

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• Siphons (tubes to carry water into and out of the
  animal)
• A muscle holds the valves (shells) together
• No head, radula or true eyes (eyespots only)
• Gills for getting oxygen from the water
• Open circulatory system

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Above left Elephant trunk clams, named for their
large foot Above right an opened oyster commonly
enjoyed raw or cooked as a delicacy Lower right
Scallop showing off its many primitive eyes
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Giant clams have zooxanthellae, just like corals
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Class Gastropoda

• Gastropod means stomach-foot
• They usually have one shell, e.g. snails
• They have a variety of feeding methods some are
  herbivores, some carnivores, some parasites
• Some cone snails inject a venom that can be fatal
  to humans

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• Snails have a hard door called an operculum
• Internal fertilization and are often
  hermaphrodites
• Use a radula for feeding

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Gastropod Diversity
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Also in Class Gastropoda The Nudibranch!

• Nudibranch means naked gills
• They have evolved to have no shell

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• Toxic and have bright beautiful colors as a
  warning to predators

• The feathery parts on their backs are their gills
• Two rhinophores that taste the water around
  them to sense their environment

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Top 5 reasons why Nudibranchs are so cool

• 5. They are amazing colours
• 4. They can eat toxic sponges without being
  harmed, but can transfer the toxin to a predator
  if bitten
• 3. Hermaphroditic nudibranchs battle to be the
  one to inject the other with sperm.

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• 2. They can eat nematocysts from corals and
  anemones without getting stung. The next thing
  that touches them gets the sting!
• 1. A nudibranch can eat algae and take the
  chloroplasts into its own body. It can then
  perform PHOTOSYNTHESIS!

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Class Cephalopoda

• Their name means
• head foot
• E.g. Octopus, squid, cuttlefish

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• They have 8 (or more) arms
• They can push a jet of water out their siphon,
  allowing them to move quickly
• An ink sac allows them to eject ink as decoy

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• The Nautilus has a shell with chambers that
  allows it to change depth easily (they are great
  hunters)

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• Many cephalopods have no shell
• Squid and cuttlefish have a hard part inside
• Octopus have no hard parts except for their mouth

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• Cephalopods have a very well developed nervous
  system
• nerves can carry messages TEN times faster than
  in humans
• Their eye is complex and has 180 degree vision
  out of the sides of their heads

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• They have a developed brain and can solve
  problems
• Mouth is called a beak
• They have internal fertilization and have
  separate sexes
• male has a special tentacle used to put sperm
  packets inside the female
• Squid mate in a big group

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• Female octopus lay thousands of eggs in a cave
  and guards them until she dies

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Octopus
Octopus on the beach
Octopus beak
Swimming Octopus
Octopus arm in detail
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• Many have photophores that allow them to produce
  light
• Most also have chromatophores that allow them to
  change color to match their background

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Squid
Caribbean Reef Squid
Tentacles of a giant squid
Calamari a deep fried squid dish
Squid eye and gills
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Squid Fact

• The largest squid ever caught was a 10 m long
  Colossal Squid off the coast of New Zealand and
  weighed in at 495 kg. Colossal Squid are larger
  than the giant squid found off the Mexican coast
  and are thought to grow in size to 13 meters!