Phylum Mollusca

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Phylum Mollusca
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Phylum Mollusca

• Bilateral symmetry
• Body Cavity - Coelomate
• Body has three distinct regions
• Visceral mass - central section, which contains
  the body's organs
• Mantle - Means cloak in Greek. Wraps around the
  visceral mass, secretes shell. Mantle cavity
  -space between mantle visceral mass.
• Foot - Ventral, muscular and prominent.
• Functions
• Locomotion - Bivalvia use to dig into sand
• Securing food - modified into a tentacle in
  Cephalopods

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Digestive System

• Radula - rasping organ in Gastropods, Beak in
  CephalopodsAll mollusks except Bivalvia have
  this structure.
• Used to scrape algae off rocks (Gastropoda) or as
  a weapon to puncture holes in prey (Cephalopoda)
• Has mouth, esophagus, stomach, intestine and
  anus.
• Digestive gland secretes enzymes into the gut.

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Excretory System

• Nitrogenous wastes dumped into coelom. Cilia in
  nephridium cause fluid (wastes and nutrients) to
  move through nephridia.
• Nutrients are reabsorbed wastes empty into the
  mantle, then removed.

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Circulatory System

• Open system for all except Cephalopoda.
• Dorsal aorta - Coelom - restricted to the region
  around the Dorsal Aorta.

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Respiratory System

• Gills located in their mantle cavity
• Cilia beat continuously causing a steady stream
  of water to pass over the gills. Gills also trap
  food

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Nervous System

• Ring of nervous tissue around esophagus
• Two sets of ventral nerve fibers
• Nerve fibers maybe quite large - squid
• Photoreceptors, Chemoreceptors and tactile
  receptors

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Reproductive System

• Male and female
• External fertilization

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Major Classes

• Class Gastropoda
• Class Bivalvia
• Class Cephalopoda
• Class Polyplacophora

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Class Gastropoda - Snails and slugs

• Examples Nudibranch - Sea slugs
• Mantle secretes hard protective shell.
• Some don't have shell.
• All terrestrial mollusks are in this class, but
  most members are marine.
• Terrestrial mollusks don't have gills.

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Class Gastropoda - Snails and slugs

• Uses Radula to scrape algae for food
• Foot adapted for locomotion. It forms a slimy
  path then ungulates foot (wave like motion)
• Eyes are located on a pair of stalk like
  tentacles on the head

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Class Bivalvia - Clams, oysters and scallops

• Examples - Oysters, Scallops, Clams,
• Name means bi - "two", valva - "part of a door"
• Edge of Mantle secretes a two part hinged shell.
  Composed of Calcium Carbonate. Shell shows growth
  lines.
• No distinct head region, but have a central
  ganglia above foot
• Most are Sessile, exception scallops and
  shipworms. Most are Filter feeders

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Class Bivalvia

• Nervous System- touch and photoreceptors
• Muscular System
• Adductor muscles connect the two valves together.
• Muscular foot used to dig into the sand and
  locomotion
• Nutrition - Filter feeders.
• Use a hollow tube called a siphon to pull in
  water. Water is then drawn over the gills then
  out the excurrent siphon.

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Class Bivalvia

• Reproduction
• Sexual, Most species have separate sexes, few
  hermaphrodites. Shed sperm and eggs into water.
  Fertilization is external.
• Zygote develops into a free swimming trochophore
  larva.
• Teredo (Shipworm) - feeds on cellulose that it
  ingests

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The Atlantic Shipworm (Teredo navalis),
introduced in 1913, resulted in 3.1 billion (in
today's dollars) in damage to wooden structures
on the Bay between 1919 and 1921.
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Class Polyplacophora - chitons

• Shell is embedded in mantle
• Mantle cavity has two lateral grooves on each
  side of body where gills are located.
• Use Radula to scrap algae
• Reproduce externally, Separate sexes

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Cephalopods(head feet)Invertebrate
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Cephalopods History

• appeared some time in the late Cambrian several
  million years before the first primitive fish
  began swimming in the ocean
• Scientists believe that the ancestors of modern
  cephalopods (Subclass Coleoidea octopus, squid,
  and cuttlefish) diverged from the primitive
  externally shelled Nautiloidea (Nautilus) very
  early - perhaps in the Ordovician, some 438
  million years ago.

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Cephalopod Hist. cont

• Cephalopods were once one of the dominant life
  forms in the world's oceans
• Today there are only 650 or so living species of
  cephalopods (compare that with 30,000 living
  species of bony fish). However, in terms of
  productivity, some scientists believe that
  cephalopods are still giving fish a run for their
  money

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Cuttle fish Sepioloidea lineolata
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Squid Taningia danae
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Octopus Hapalochlaena lunulata
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Cephalopods

• Fast swimming predatory animals
• Extremely intelligent
• Cephalopods foot is divided into tentacles
• squid10 tentacle
• octopus8 tentacle
• cuttle fish6 or more tentacle

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Cephalopods distinct structures

• Cephalopods have large, well developed eyes that
  form images
• Tentacles are covered with suckers for seizing
  and holding prey
• Cephalopods have a rasp like structure in their
  digestive tract called a radula for breaking down
  food
• Cephalopods mouth has two strong beaks for
  tearing its prey apart.
• Cephalopod is fitted with a funnel like
  structure that fills with water and ejects it
  acting like a jet propolsion

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Cephalopods masters of deception

• Able to change multi colors
• Can expand and contract pigment cells in its skin
• Chromatophores(color cells) give the cephalopod
  the ability to change.
• Can eject ink when alarmed causing the enemy to
  be temporarily blinded. The ink also inactivates
  predators chemical receptors used for detecting
  prey.

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Cephalopods Diet

• Feed on crabs, shrimp, fish, and other cephalopods

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Cephalopods Habitat

• Intertidal to abyss
• Polar to tropics
• In other words they are found everywhere

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The Infamous Giant SquidArchiteuthis
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Giant Squid

• Giant squid get up to 60 feet (20 m) in length
  and easily hold the record as the worlds largest
  invertebrate
• Despite the size of these beasts no one has ever
  seen one alive in its natural environment
• Main Diet of the sperm whale
• Giant squid were once mistaken for sea monsters
  in sailing days

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Cuttlefish (how to maintain in a hobbyist
environment)

• Filtration slightly over-filter the tank
• Canister filters, turf scrubbers, hang on the
  backs, wet/drys, fluidized bed filters or
  whatever the latest flavor of filter is, can all
  be used on a cuttlefish tank
• Undergravel filters are not advised as cuttlefish
  often dig in gravel which could create dead spots
• Protein skimmer would be recommended
• Water changes of about 20 should be done monthly

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Cuttlefish (how to maintain in a hobbyist
environment)

• Lighting
• can be kept to a minimum to reduce algae growth
• never suddenly turn the lights on or the
  cuttlefish may ink

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Cuttlefish (how to maintain in a hobbyist
environment)

• Temperature
• room temperature is fine since cuttlefish are
  found throughout the world

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Cuttlefish (how to maintain in a hobbyist
environment)

• Tankmates
• A group of cuttlefish can be raised together in a
  large aquarium
• if food is limited, cephalopods can be
  cannibalistic

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Cuttlefish (how to maintain in a hobbyist
environment)

• Tank size
• of course, depends on the size, and the
  potential size of the animals that you are
  planning to keep
• 40 gallons per 15 inch full grown cuttlefish will
  be safe

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Cuttlefish (how to maintain in a hobbyist
environment)

• Feeding
• Cuttlefish primarily eat live marine fish and
  crustaceans in nature and these are ideal foods
  for them in captivity as well(live food is the
  best)
• Only feed them what they what they can eat in a
  short time.

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