Mollusca or Mollusks

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Mollusca or Mollusks

• Presented By
• Justen Maley
• Genevieve Lambert
• Eric Hoosier

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History of Mollusks

• The name Mollusca was first used by French
  zoologist Cuvier in 1798
• He used this name to describe Squid and
  Cuttlefish because it derives from the Latin
  Mollis meaning soft
• Later on the true affinities between these
  species and other Molluscs, such as Snails and
  Bivalves, were fully recognized

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Interesting Facts

• Mollusks are one of the three most successful
  groups in the animal kingdom
• Over 160,000 species have been discovered
• 128,000 of those species are still living
• 35,000 are recorded as fossil species

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There are four important lineage of Mollusks

• Bivalves (Clams and Mussels)
• Gastropods (Slugs and Snails)
• Cephalopods (Squids and Octopuses)
• Polyplacophora (Chitons)

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Mollusk Body Plan

• The mollusk body plan is based on three major
  components.
• 1. The foot, a large muscle that is located at
  the base of the animal and is usually used in
  movement.
• 2. The visceral mass, the region that contains
  the most of the main internal organs and external
  gills.
• 3. The mantle, a tissue layer that covers the
  visceral mass and that secretes a shell made of
  calcium carbonate.

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Mollusk Body Plan

• Mollusks may have one, two, eight, or no shells.
  When shells are present, they function to protect
  the animal.
• The muscular foot itself, much like our tongue,
  may function as a hydrostatic skeleton.

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Ecological Roles

• Mollusks are important commercially. Clams,
  mussels, and scallops are farmed or harvested
  from the wild in many parts of the world and used
  as food for humans. When they are sold
  commercially bivalves are known more commonly as
  Shellfish.
• Pearl oysters that are cultivated from the wild
  are the most common source of natural pearls used
  in jewelry.

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Ecological Roles

• Mollusks are among many of the protostomes that
  act as consumers, predators, and scavengers in
  marine food chains.
• Mollusks and other protostomes are important in
  near-shore habitats with either rocky surfaces or
  soft substrates such as sand or mud.
• Along coastlines outside the tropics, protostomes
  are consumers of algae and other primary
  producers and are key players in virtually every
  shallow-water marine environment on the planet.

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Bivalves

• Bivalves are named because they have two separate
  shells made of calcium carbonate secreted by the
  mantle. When the shell is closed it protects the
  mantle, visceral mass, and foot.
• Bivalves live in the ocean, though some
  freshwater forms are known.
• Because most bivalves live on or under the ocean
  floor, and because they have a hard shell, their
  bodies are often buried in sediment after death.
  Because of this, the Bivalvia lineage has the
  most extensive fossil record of any animal plant
  or fungal group.

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• Clams, part of the Bivalves

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Gastropoda

• The gastropods belly feet are named for the
  large, muscular foot on their ventral side.
• Terrestrial snails can retract their foot and
  body into a shell when they are attacked or when
  their tissue begin to dry out
• Land slugs lack shells but often contain toxins
  or foul-tasting chemicals to protect them from
  being eaten.
• There are about 70,000 species of gastropods
  known.

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• Snail, part of the Gastropods

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Cephalopoda

• The cephalopods head-feet have a well developed
  head and foot that is modified to form tentacles
• They have large brains and image forming eyes
  with sophisticated lenses.

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• Squid, part of the Cephalopods

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Polyplacophora (Chitons)

• Polyplacophora means many-plate-bearing.
• Chitons have eight calcium carbonate plates along
  their dorsal side which from a protective shell.
• They are usually found on rocky surfaces in the
  intertidal zone, where rocks are periodically
  exposed to air at low tides.

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• Chiton, part of the Polyplacohora

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Additional Uses for Mollusks

• The most common use humans have for mollusks is
  that we eat them.
• The most eaten types of mollusks are clams,
  oysters, scallops and mussels.
• Some people also enjoy eating octopus and squid.

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More uses

• Another popular use for mollusks is for the
  making of jewelry.
• Oysters contain pearls, which are very precious
  jewels in the world today.
• People also use the shells and decorate them to
  sell them as crafts.
• Scallop shells are used as a religious symbol of
  Methodism.

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Helpful to Everyone

• Mollusks are important to humans as well as other
  animals as food. Some shells are a major source
  of calcium for some birds. The consumption of
  mollusks goes back centuries. Indeed, humans
  found a way to use oysters to increase the food
  supply indirectly The crushed shells attract
  micro-organisms that kill the nematodes that are
  agricultural pests. Mollusks also nourish humans
  culturally. Rare and beautiful shells have been
  prized throughout history and many are still
  extremely valuable to collectors. In some early
  cultures mollusk shells served as money. Humans
  are undoubtedly more harmful to mollusks
• than the reverse.

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Pollution Problems with Mollusks

• Because bivalves are filter feeders, they tend to
  accumulate pollutants and in many places they are
  collected and analyzed as a means for monitoring
  water pollution.
• Pollution effects on bivalve mollusks are
  particularly apparent in coastal waters, though
  ocean dumping can contaminate offshore stalks as
  well. Coastal pollution has in recent decades
  become a significant and growing problem, calling
  for greater understanding of the effects of mans
  activities on habitats and increased awareness of
  this aspect of environmental degradation.

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Effects on the Brain

• Mollusks have been used in recent studies to
  determine the effects of Serotonin on the brain.
• Serotonin is a neurotransmitter present
  throughout the body. When nerve cells containing
  it are activated, serotonin is released. It
  travels and stimulates other nerve cells,
  enabling their message to spread through the
  nervous system.
• Two new serotonin metabolites were found in
  marine mollusks. Scientists are studying this to
  see whether it may be able to treat depression
  and other disorders.

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Marine Mollusks and the Skin

• Human contact with marine mollusks such as
  shellfish, marine snails, octopuses, and squids
  may result in human illness including
  dermatologic disorders. These range from minor
  traumatic injury of the skin to more serious
  systemic illnesses that include dermatologic
  manifestations. Notable among these are
  dermatologic manifestations of illness caused by
  toxins from ingested mollusks, stings of the cone
  snail, and envenomation by the bite of the
  blue-ringed octopus. Cone snail and blue-ringed
  octopus envenomations, although rare, can be
  deadly due to neuromuscular paralysis. Management
  of dermatologic illnesses caused by marine
  mollusks depends upon the nature of the exposure.
  Attention to local measures is usually sufficient
  for minor cuts and abrasions. Conversely, cone
  snail and blue-ringed octopus envenomations
  require immediate attention, possibly including
  cardiopulmonary resuscitation.