MOLLUSCA

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MOLLUSCA
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Introduction

• At this point in our phylogenetic tree, we branch
  into two systems
• This will also be our introduction to coelomates!
• Starts with Mollusks!!!

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Introduction

• Phylum Mollusca is the second in size to
  Arthropoda.
• Their members are greatly diverse in their
  structure, physiology, and habits
• So, what brings them together?

• Mollusk comes from the Latin word mollis
  meaning soft
• Basic Body Plan
• Mantle
• Outside covering organ which secretes the shell
  contains vital organs
• Shell
• Used for protection and structure
• Foot
• Extended fleshy mass from the body

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IntroDuction

• There are five major classes you need to know for
  this phyla
• A) Class Bivalvia (ex. Clams, oysters)
• B) Class Gastropoda (ex. Snails, slugs)
• C) Class Scaphopoda (ex. Tooth shell)
• D) Class Cephalopoda (ex. Squid, octopus)
• E) Class Polyplacophora (ex. Chitons)

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Class Bivalvia

• Include clams, oysters, mussels, scallops, etc.
• Contain two shells (valves)
• Can be freshwater or saltwater
• Most are mobile, but a few are sedentary

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Class Bivalvia

• In bivalves, the foot (which contains a majority
  of the digestive organs) is expelled by gorging
  it with blood and used for movement and burrowing
  in the sand.

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Class Bivalvia

• The gills (ctenidia) are unusually large and are
  used for both respiration and as a food-gathering
  device. Palps also aid in orienting food for the
  mouth.

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Class Bivalvia

• The flow of water in and out of the bivalve is
  created and maintained through the excurrent and
  incurrent siphons (part of the mantle)

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Class Bivalvia

• To control the movement of the valves, the
  bivalve uses two large muscle clumps (anterior
  and posterior adductor muscles). (For
  dissection, you will need to be patient)

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Class Bivalvia

• To expose the other organs, gently open up the
  foot

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Class Gastropoda

• This is the largest and most widely-distributed
  of the molluscan classes. The name "gastropoda"
  literally means "stomach-foot" (these animals
  crawl around on their stomach).
• Examples of gastropods include snails, limpets,
  slugs, and nudibranchs.
• Gastropods are found on land and in both fresh
  and salt-water habitats.
• Depending on the species, they may be
  predacious, herbivorous, or scavengers.

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Class Gastropoda

• Gastropods, like other mollusks, have a peculiar
  file-like tongue called a radula
• Gastropod larvae undergo a twisting, or torsion,
  that brings the rear of the body (mantle cavity,
  gills, and anus) to a position near the head and
  results in the twisting of internal organ
  systems. In many this twisted form is retained by
  the adult in others it is partially lost.

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Class Gastropoda

• Reproduction is variable, but most gastropods
  have separate sexes. Fertilization of the egg
  occurs in seawater. Some gastropods are
  hermaphrodites (having both sexes in the same
  individual) and some are protandric
  hermaphrodites, i.e., they are male first and
  become female as they age

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Class Scaphopoda

• Scaphopods are a small group of mollusks commonly
  known as "tooth shells" or "tusk shells".
• They are rarely seen alive since they're
  relatively small and burrow in the sediment.
• Microorganisms make up the bulk of their diet.
  Adhesive tentacles sometimes capture larger food.
  
• Tooth shells are all marine.
• Examine the scaphopod shells on display.

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Class Cephalopoda

• The term "Cephalopoda" literally means
  "head-foot".
• Octopods, squid, cuttlefish, and nautili are
  examples of cephalopods.
• Most of the adaptations seen in the cephalopods
  are related to their swimming and predatory
  behavior.
• All are marine forms

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Class Cephalopoda

• The mouth is surrounded by a circlet of tentacles
  (or arms).
• The shell is usually internalized (squid pens and
  the cuttlebone of cuttlefish) or absent
  (Octopus) only the nautili retain a shell.
• Cephalopods are voracious carnivores. Their eyes
  are among the best of the invertebrates and eight
  or more arms can quickly encircle prey.
• A parrot-like beak with poison glands subdues and
  tears prey.

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Class Polyplacophora

• Polyplacophorans (chitons) have shells composed
  of eight overlapping plates that at least
  partially covered by the mantle.
• They are almost prehistoric in appearance.
• Most feed on algae and other encrusting
  organisms by scraping them off the surface of
  rocks with a radula.
• They are common inhabitants of the intertidal
  zone.

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• ENJOY THE DISSECTION!!!!