Phylum Molluska

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• Phylum Molluska

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Mollusks

• Non-segmented Bodies
• Next to Insects, Most Successful Animal

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Mollusks are widespread

• One of the most successful of all animal phyla.
• Abundant in marine, freshwater, and terrestrial
  habitats.

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All Mollusks Share the Following Characteristics.

• 1. Body Cavity
• 2. Symmetry
• 3. Organ System
• 4. Three-Part Body Plan

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Three-Part Body Plan

• Foot
• Mantle
• Visceral Mass

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Characteristics of a Mollusk

• Objective Explain the Evolutionary Relationship
  Between Mollusks and Annelids.
• Both were the first to develop a true coelom.
• Trochophore Larva.

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Picture of Trochophore Larva
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Organ Systems of Mollusks

• Objective Describe the Respiratory, Circulatory,
  and Excretory Systems of Mollusks.

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Respiration

• Breathe with ciliated gills located in mantle
  cavity.
• Extracts 50 of dissolved oxygen from water.
• Some lack gills but mantle cavity functions as
  simple lung.

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Circulation

• 3-chambered heart
• Open Circulatory System
• Only octopi and squids have closed circulatory
  system.

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Excretion Early developers of an efficient
excretory system.

• Use coelom as a refuse dump
• Nephridia filters wastes
• Found in all coelomates except arthropods and
  chordrates.
• Wastes out, molecules in.

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Organs of a Snail
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Classifying mollusks

• Two Shelled Bivalve
• One Shelled Gastropoda
• No Shell Cephalopods

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Section Objective

• Describe four classes of Mollusks.

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Four classes of Mollusks

• There are actually seven different classes of
  mollusks. But the four major are
• Polyplacophora
• Bivalves
• Gastropods
• Cephalopods

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Bivalve
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Gastropod
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Cephalopod
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Polyplacophora

• This class is one of the smaller classes and
  still has most of the characteristics of their
  ancestors.

A chiton, of the class Polyplacophora
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Bivalves
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clam
oyster
mussel
scallop
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Bivalves

• Bivalves are characterized by two valves
  (shells), and siphons.

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Anatomy of Bivalve
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Movement

• Bivalves use their foot to dig into the sand.
• They may also close their valves rapidly,
  creating jet propulsion.

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Feeding

• A bivalve filter feeds by sucking in sea water
  with one siphon and expelling it out the other.

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Respiration

• Cilia that cover the gills draws water through
  one siphon, over the gills, and out the other
  siphon.
• Bivalves also breath with the same gills that
  they feed with.

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Exception

• One bivalve, the teredo, doesnt filter-feed, it
  digests cellulose in wood using symbiotic
  protists in its intestine.

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Reproduction

• Bivalves reproduce sexually.
• The reproduce by shedding sperm and eggs into the
  water.
• Bivalves can be either male or female, or the may
  be hermaphroditic.

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Gastropods
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Gastropods

• They have a pair of tentacles, with eyes on its
  head
• most have a single shell

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Gastropoda

• The class Gastropoda include snails and slugs.

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Movement

• A gastropods foot is adapted for locomotion.
• Terrestrial species secrete mucus to create a
  path to glide across.

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Recognizable Features
Eye

• Most gastropods have two tentacles where the eyes
  are located on their head.

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Recognizable Features (cont.)

• Except for slugs and nudibranchs (sea slugs),
  most gastropods have a single shell.

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Torsion

• The visceral mass of gastropods rotate 180
  degrees during development.

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Respiration

• Gastropods respire using gills (aquatic species),
  directly through the skin or using the mantle
  cavity as a primitive lung (terrestrial species).

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Feeding

• Gastropods have many different feeding habits
• Scraping algae off rocks (Radula)
• Eating leaves
• Eating other animals

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Snails Mating
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Cephalopods

• Head-foot

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Head-foot

• Cephalopods include squids, octopuses,
  cuttlefishes, and nautiluses.
• Most of a cephalopods body is a large head
  attached to tentacles (the foot).

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Squid
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Octopus
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Octopus
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Octopus
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Cuttlefish
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Nautilus
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Feeding

• Cephalopods are marine predators that feed on
  fish, mollusks, crustaceans, and worms.
• Prey is snared by suction cups or hooks on the
  tentacles.

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Movement

• Cephalopods swim with their tentacles.
• In addition, octopuses and squids use jet
  propulsion.

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Intelligence

• Cephalopods are the most intelligent
  invertebrates.
• Octopuses can be easily trained.
• See lab page 125 of Binder

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Reproduction

• Cephalopods are either male or female.
• Male cephalopods use a modified tentacle to
  transfer a packet of sperm from its mantle cavity
  into the females. See Video

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SECTION REVIEW

• Question 1. What evidence suggests that mollusks
  and annelids share a common ancestor?
• A. They both have the trochophore larval stage

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SECTION REVIEW

• Question 2. Describe how a nephridium functions.
• A. a nephridium is a tiny tubular organ that
  filters wastes from the coelom of certain
  invertebrates.

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SECTION REVIEW

• Question 3. Why would you expect a mollusks blood
  pressure to be quite low?
• A. Since most mollusks have an open circulatory
  system their blood isnt always contained so the
  blood pressure is low.

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SECTION REVIEW

• Question 4. Define torsion and what mollusk group
  it occurs on.
• A. Torsion- a 180 twist of the visceral mass
  during the embryonic development of gastropods

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SECTION REVIEW

• Question 5. Contrast the feeding habits of
  cephalopods and gastropods.
• A.Gastropods are mostly herbivores while
  cephalopods are skilled hunters.

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SECTION REVIEW

• A chemical pollutant accidentally spills into a
  bay. One of the effects of the chemical is that
  it paralyzes cilia. The next day almost all of
  the oysters in the bay are dead. Explain why.

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Answer

• Oysters have cilia over their gills that draws
  water into the gills providing the oyster with
  food and oxygen from the water. If their cilia
  is paralyzed, they can not draw in the necessary
  oxygen and food to survive.

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SECTION REVIEW

• Squids are the fastest swimmers of all aquatic
  invertebrates. Name two structural adaptations
  in squids that may have enhanced their swimming
  ability.

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Answer

• Cephalopods use jet propulsion to swim. They do
  so be drawing water into their mantle cavity,
  closing it quickly and expelling it out of a
  siphon. They also lack an external shell so can
  move easily and freely without any restriction.

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The End
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Mollusks and Annelids

• Chapter 29
• Section 2 Annelids

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Section Objective

• Describe three classes of Annelids.

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Polychaetes

• Parapodia
• swim, burrow, or crawl
• gas exchange more efficient
• either male or female
• external fertilization
• ciliated trochophore larvae
• juvenile polychaetes

• segmented
• free-swimming predators
• excavate tunnels
• pumping water or scraping bottom
• well developed head
• beautiful

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Earthworms Oligochaetes

• Terrestrial
• specialized scavengers
• material passes to gizzard
• unabsorbed material
• characteristic castings
• eats own weight in soil each day

• Lack distinctive head region
• no eyes
• light-sensitive and touch-sensitive organs
• detect moisture

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Leeches

• predators, or scavengers
• Parasitic
• suck blood
• remain on host for long periods

• Flattened body
• 2.5-5.0 cm
• one species-30.5 cm
• segmented
• suckers at both ends
• movement
• feeding

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Section Objective

• Identify the internal structures of an earthworm.

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Internal Structures of Earthworms

• Pharynx
• soil taken in
• Esophagus
• passes through
• Crop
• temporary storage

• Gizzard
• grind soil
• break up organic matter
• Intestine
• food molecules absorbed
• passed to blood stream

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Annelids

• Are they more than just slimy, icky little
  worms????

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What Classifies Annelids?

• 1) Body Cavity

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• 2) Segmentation

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3)Organ Systems

• Organ Systems

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4) Bristles setae parapodia
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Organ Systems of Annelids

• Section Objective
• Describe the circulatory system in annelids.

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Circulatory System

• Closed Circulatory Systems
• Annelids hearts are basically enlarged blood
  vessels that pump blood

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Earthworm Circulatory System
Earthworms have five pairs of hearts (YUK)
Worms Heart Beating
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Annelid Respiratory System

• Annelids have no specialized respiratory organs
• They exchange oxygen and carbon dioxide directly
  through their skin.

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Excretion

• Annelids use ciliated, funnel-shaped nephridia
  for excretion, each segment has a pair that
  collects waste.

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General Worm Info.

• There are apx. 4,400 species of worms
• There are 2,700 species of earth worm
• There are 650 know species of leeches

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More General Info.

• Worms have been around for 120 million years
• Cleopatra called worms sacred

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Earth Worms
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Earth worms

• In South America earth worms can be eight feet
  long, be .75 inches in diameter and weigh over
  one pound!
• Earth worms have no teeth, just very strong
  stomachs

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Earth Worms

• Earth worms have 100 or more body segments
• they have no lungs they breath through their skin
• the body of an earth worms is 70 protein
• Their biggest predators are birds

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Marine worms
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Fan worms are types of marine worms
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Marine Worms

• Many marine worms are tube worms
• they come in a large array of colors
• the majority of them are less than ten
  centimeters long

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Bearded worm
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Marine worms

• Marine worms adapt very rapidly to their
  environment

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Leeches
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Leeches

• The leech has 32 brains
• leeches are used in medicine and the first was
  used in India about 1000 B.C.

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Leeches

• Leeches make their own anesthetic hence their
  bite is painless
• leeches drink up to five times their body weight
• most leeches live in fresh water

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Earthworm Digestion

• Soil enters the digestive system through the
  mouth into the Pharynx, then through the
  esophagus, then into the crop, it enters the
  gizzard next, and finally into the intestine
  before leaving the body.

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Earthworm Reproduction

• Earthworms are Hermaphrodites, They reproduce by
  joining at the Clitellum ventrally (head to tail)
  . At the same time both worms release sperm into
  the other. Then the clitellum releases a mucus
  membrane forming a cocoon.

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Earthworm Brain

• The brains coordinates the muscular activity of
  each body segment, thus controlling total body
  movement

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Earthworm Movement

• Worm fastens itself to the ground using its
  Setae, it then contracts the circular muscles in
  from of the attachment, then retracts the muscles
  to elongate, anchors itself with a front anchor,
  then contracts the muscles (pull)

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RAQ 1

• If you have two worms with different external
  characteristics, how can you tell if either is an
  annelid?

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Answer

• You can tell which is which by the presence of
  segmentation, and also the presence of setae.
  Annelids have both of these characteristics that
  distinguish them.

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RAQ 2

• How are the circulatory systems of a human and an
  earthworm similar?

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Answer

• Both humans and earthworms have a closed
  circulatory system with blood vessels and their
  blood contains hemoglobin.

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RAQ 3

• Contrast polychaetes with leeches.

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Answer

• Polychaetes have parapodia and setae. Leeches
  lack both. Leeches are flat and lack a definite
  head end. Polychaetes have a definite head-end.
  Some leeches are parasitic. Polychaetes are not
  parasitic.

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RAQ 4

• A mutation results in the birth of an earthworm
  that lacks moisture-sensing cells in its skin.
  Explain why this earthworm is less likely to
  survive than one with the sensory cells.

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Answer

• In order for earthworms to breath their skin
  needs to be moist so oxygen and carbon dioxide
  can diffuse. If they lack those sense organs
  that allow them to detect moisture, then they do
  not have the ability to realize when it is moist
  or dry.

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Vocabulary for Chapter 29

• Adductor Muscle- attachment between the two
  valves of a mollusk that causes the shell to open
  and close.
• Closed circulatory system- system in which the
  blood does not leave the blood vessels and
  materials pass in and out by diffusing across the
  walls of the vessels.

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Cont.

• Open circulatory system- system in which blood
  leaks out of blood vessels and bathes the body
  tissues.
• Parapodia- fleshy appendage of marine annelids.
• Setae- external bristles of annelids.
• Siphon- hollow tube of bivalves used for sucking
  in and expelling sea water.

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Vocab. cont.

• Gizzard- a portion of the digestive tube of
  earthworms where strong muscles grind up the
  organic material in ingested soil.
• Mantle Cavity- space between the mantle and the
  visceral mass of mollusks.
• Nephridia- tiny tubular organ of excretion that
  filters cellular wastes from the coelom of
  certain invertebrates.

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The End