The Invertebrates

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The Invertebrates
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Phylum Porifera
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General Characteristics

• 9,000 species (100 live in fresh water the rest
  are marine).
• Sessile, and asymmetrical.
• Resembles a sac perforated with holes.
• Porifera (poh-RIF-ur-uh) means pore bearers.
• Water is drawn through the pores into a central
  cavity spongocoel, then flows out of the sponge
  through a larger opening called the osculum. This
  is how the sponge carries out feeding,
  respiration, circulation, and excretion.
• Suspension-feeders- collect food particles from
  the water passed through some kind of
  food-trapping equipment.
• Sponges have a simple skeleton. In harder
  sponges, the skeleton is made up of spicules,
  (spike-shaped structures), made up of calcium
  carbonate or glasslike silica. Softer sponges
  have an internal skeleton of spongin. (bath
  sponges)

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• Lining the inside of the body are flagellated
  choanocytes (collar cells). The flagella create
  a water current, collars trap food particles and
  ingest them by phagocytosis. Amoebocytes take
  nutrients to other cells.
• Sponges can reproduce either sexually or
  asexually.
• Most sponges are hermaphroditic and produce both
  eggs and sperm by meiosis. The eggs are
  fertilized inside the body (internal
  fertilization). Sperm are released from one
  sponge and carried by water currents to another
  sponge. They form a zygote and later a larva
  which is motile and uses the water current to
  settle on the sea floor. This sponge is not
  genetically identical to its parents.

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• Sponges can reproduce asexually by budding where
  part of the parent sponge breaks off, settles to
  the sea floor, and grows into a new sponge. This
  new sponge is genetically identical to its
  parent.
• Least complex of all animals, capable of
  extensive regeneration (replacement of lost
  parts).
• Lack organs, cell layers, no nerves or muscles.
• Individual cells can sense and react to changes
  in the environment.
• Sponges provide habitats for marine animals such
  as snails, sea stars, and shrimp. Sponges also
  form partnerships with photosynthetic bacteria,
  algae, and plantlike protists. (Mutualism both
  partners benefit).

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Cnidarians
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General Characteristics

• Cnidarians (ny-DAYR-ee-ans) are soft-bodied,
  carnivorous animals that have stinging tentacles
  arranged in circles around their mouths. They
  are the simplest animals to have body symmetry
  and specialized tissues.
• Members of phylum Cnidaria include hydras,
  jellyfish, sea anemones and coral animals. Some
  live as individuals, while others live in
  colonies in freshwater and oceans.
• Cnidarians get their name from cnidocytes, or
  stinging cells, that are located along their
  tentacles. Cnidarians use these for defense and
  to capture prey. Within each cnidocyte is a
  nematocyst. A nematocyst is a poison-filled,
  stinging structure that contains a tightly coiled
  dart. When a shrimp or small fish brushes up
  against the tentacles, thousands of nematocysts
  explode into the animal, releasing enough poison
  to paralyze or kill the prey.

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Form Function

• Cnidarians are radially symmetrical. They have a
  central mouth surrounded by numerous tentacles
  that extend outward.
• Cnidarians have a life cycle that includes two
  different-looking stages a polyp and a medusa.
• Polyp
  Medusa

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• A polyp is a cylindrical body with arm-like
  tentacles. Polyps are sessile with their mouth
  pointing upward.
• A medusa has a motile, bell-shaped body with a
  mouth on the bottom.
• Cnidarians have a body wall that surrounds an
  internal space called a gastrovascular cavity.
  This is where digestion takes place. Nutrients
  are transported through the body by diffusion.
• Cnidarians respire and eliminate their waste by
  diffusion through their body walls.
• They are able to gather information from their
  environment using specialized sensory cells or a
  nerve net. They can detect stimuli such as light
  and touch.

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Reproductive Cycle
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• Cnidarians move in different ways. Sea anemones
  have a hydrostatic skeleton (layer of circular
  and longitudinal muscles) while medusas move by
  jet propulsion.
• Jellyfish (Class Scyphozoa) means cup animals.
  Jellyfish live their lives primarily as medusas.
  The polyp form is limited to the larval stage,
  and no colonies form. Jellyfish reproduce
  sexually and may grow up to 4 meters in diameter
  with tentacles more than 30 meters long.
• Hydras (Class Hydrozoa) contains hydras and other
  related animals. The polyps of most hydrozoans
  grow in branching colonies. Within the colony,
  polyps are specialized to perform different
  functions. (ex. Portugese man of war). Hydras
  are different from other cnidarians in their
  class as they lack a medusa stage. Instead they
  live as single polyps and reproduce asexually or
  sexually.

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• Sea Anemones and Corals (Class Anthozoa) These
  flower animals include the sea anemones and
  corals, animals that have only the polyp stage in
  their life cycle. Many species are colonial, or
  composed of many individual polyps.

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The Worms
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The Flatworms

• The phylum Platyhelminthes (plat-ih-hel-MIN-theez)
  consists of the flatworms.
• Flatworms are soft, flattened worms that have
  tissues and internal organ systems. They are the
  simplest animals to have three embryonic germ
  layers, bilateral symmetry and cephalization.
• Flatworms are known as acoelomates meaning
  without coelom. A coelom is a fluid filled body
  cavity that is lined with tissue.
• Flatworms are thin therefore materials can pass
  easily into and out of their body cells. They
  rely on diffusion for respiration, excretion, and
  circulation.

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• Flatworms are free-living or parasitic.
• Free-living flatworms can be carnivores, or
  scavengers. They have a digestive cavity with a
  single opening or a mouth, through which food and
  wastes pass.
• Parasitic worms feed on blood, tissue fluids, or
  pieces of cells within the hosts body. Many
  parasitic worms obtain nutrients from foods that
  have already been digested by their host. As a
  result they have a very simple digestive system.
  Tapeworms have no digestive system.
• In free-living flatworms a head encloses several
  ganglia, or groups of nerve cells, that control
  the nervous system. Parasitic worms have a less
  complex nervous system.

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• Free-living flatworms typically move by using
  cilia on their epidermal cells and through muscle
  cells.
• There are three main groups of flatworms the
  turbellarians, flukes and tapeworms. Most
  turbellarians are free-living while the other
  flatworm species are parasites.
• Turbellarians The free-living flatworms belong
  to the class Turbellaria. Most live in marine or
  fresh water. Most species live in the sand or
  mud under stones and shells. Planarians are the
  most familiar flatworms.
• Flukes Members of the class Trematoda are known
  as flukes. Flukes are parasitic flatworms. Most
  flukes infect the internal organs of their host.
  (ex. The blood fluke Schistosoma mansoni needs
  two hosts a human and a snail and causes
  schistosomiasis).

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• Tapeworms Members of the class Cestoda are
  called tapeworms. Tapeworms are long, flat,
  parasitic worms that are adapted to life inside
  the intestines of their hosts. The head of an
  adult tapeworm contains a scolex with suckers or
  hooks allowing it to attach to the intestinal
  wall. Transmitted through intermediate hosts
  such as cows, fish which are improperly cooked
  and consumed by humans.

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The Roundworms

• The phylum Nematoda, are among the most numerous
  of all animals. A single rotting apple can
  contain as many as 90,000 roundworms.
• Roundworms are slender, unsegmented worms with
  tapering ends. They range in size from
  microscopic to a meter in length.
• Most species are free-living inhabiting soil,
  salt flats, sediment and water. Many others are
  parasitic and live in the hosts of almost every
  kind of plant and animal.
• Roundworms develop from three germ layers and
  have a pseudocoelom. It is a false coelom
  because the body cavity is lined partially with
  tissue.

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• Unlike flatworms, roundworms have a digestive
  tract with two openings a mouth and an anus.
• Roundworms reproduce sexually and most species
  have separate sexes.
• Their response and movement is similar to
  flatworms. They exchange gases and excrete waste
  through their body walls using diffusion.
• Parasitic roundworms include trichinosis-causing
  worms, filarial worms, ascarid worms, and
  hookworms.
• Humans get trichinosis by eating raw or
  incompletely cooked pork. Causes terrible pain
  in organs.
• Filarial worms lead to elephantiasis where the
  affected part of the body swells enormously.
  These threadlike worms affect the lymphatic
  vessels and are transmitted through biting
  insects.

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• Ascaris lumbricoides is a serious parasite of
  humans and other vertebrates which causes
  malnutrition in more than one billion people
  worldwide. It is spread through eating unwashed
  vegetables and food. This is why puppies are
  wormed when they are young.
• Hookworms affect as many as one-quarter of the
  population. They live in the soil and use sharp
  tooth-like plates and hooks to burrow into the
  skin of an unprotected foot. They enter the
  bloodstream and suck the hosts blood causing
  weakness and poor growth.

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The Segmented Worms

• Phylum Annelida refers to the ring-like
  appearance of annelids body segments.
  Earthworms, seaworms and leeches are examples of
  annelids.
• Annelids are worms with segmented bodies. They
  have a true coelom that is lined with the tissue
  derived from mesoderm.
• Annelids range from filter feeders to predators.
• Annelids typically have a closed circulatory
  system, in which blood is contained within a
  network of blood vessels.
• Land-dwelling annelids breathe through their
  moist skin, while aquatic annelids breathe
  through their gills.

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• Annelids produce two kinds of waste. Digestive
  waste passes out the anus. Nitrogenous waste
  passes out the nephridia.
• Most annelids have a well developed nervous
  system consisting of a brain and several nerve
  cords.
• Annelids move using two groups of body muscles
  longitudinal and circular. Earthworms have
  bristles called setae to prevent slipping.
  Marine annelids have paddle-like appendages
  called parapodia on each segment for swimming and
  crawling.
• Most annelids reproduce sexually. Some use
  external fertilization and have separate sexes.
  Others are hermaphrodites. They rarely fertilize
  their own eggs however.

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• Annelids are divided into three classes-
  oligochaetes, hirudinea, and polychaetes.
• The class Oligochaeta (AHL-ih-goh-keets) contains
  earthworms and their relatives. Most live in soil
  or fresh water, have streamlined bodies and
  relatively few setae.
• The class Hirudinea (hir-yoo-DIN-ee-uh) contains
  the leeches, most of which live in moist habitats
  in tropical countries. Leeches are external
  parasites that suck the blood and body fluids of
  their host.
• The class Polychaea (PAHL-ih-keets), contains
  sandworms, bloodworms and their relatives.
  Polychaetes are marine annelids, that have
  paired, paddle-like appendages tipped with setae.

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Phylum Mollusca
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Phylum Mollusca soft bodies

• Snails and slugs, oysters and clams, and
  octopuses and squids are all mollusks.
• 50,000 species mostly marine, some inhabit fresh
  water and snails / slugs live on land.
• Mollusks are soft-bodied animals, but most are
  protected by a hard shell made of calcium
  carbonate.
• Squids and octopuses have reduced shells that
  have been internalized

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• All mollusks have a similar body plan with 3 main
  parts
• a muscular foot, usually for movement, a visceral
  mass, containing most of the internal organs, and
  a mantle, a heavy fold of tissue that may secrete
  a shell.

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Class Gastropoda

• The largest of the molluscan classes (40,000 sp)
• Most gastropods are marine, but there are also
  many freshwater species and garden snails and
  slugs that have adapted to land.
• Protected by single, spiraled shells into which
  the animals can retreat when threatened.
• Shell is often conical, sometimes flattened
• Slugs and sea slugs have lost their shells during
  their evolution

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• Many have distinct heads with eyes at the tips of
  tentacles.
• Gastropods inch along by a rippling motion of the
  elongated foot.
• Most gastropods graze on algae or plant material.
  Several other groups, however, are predators.
• Aquatic gastropods respire using gills,
  terrestrial gastropods have a lung.
• Among the few invertebrate groups to have
  successfully populated the land.

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Gastropod Pics
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Class Bivalvia

• Include clams, oysters, mussels and scallops.
• Bivalves have shells divided into two halves.
• Two parts of the shell are hinged at the
  mid-dorsal line and powerful adductor muscles
  draw the two halves tightly together to protect
  the soft-bodied animal.
• Bivalves contain gills that are used for feeding
  as well as gas exchange.
• Most are suspension feeders, they trap fine food
  particles in mucus that coats the gills.

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• Water flows into the mantle cavity through the
  incurrent siphon, passes over the gills and then
  exits the mantle cavity through an excurrent
  siphon.
• No distinct head lead rather sedentary lives
• Sessile mussels secrete strong threads that cling
  to rocks
• Clams pull themselves into the sand or mud using
  the muscular foot
• Scallops dig and skitter along the seafloor by
  flapping their shells

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Bilvalve Pics
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Class Cephalopoda head foot

• Unlike sluggish gastropods and the sedentary
  bivalves, cephalopods are built for speed, an
  adaptation that fits their carnivorous diet.
• Squids and octopuses use beaklike jaws to bite
  their prey they then inject poison to immobilize
  the victim.
• The mouth is at the center of several long
  tentacles.
• The shell is usually either reduced and internal
  (squids) or missing altogether (octopuses).

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• A squid darts, usually backward by drawing water
  in and then firing a jet stream of water through
  the excurrent siphon that points anteriorly.
• Steers by pointing in different directions.
• Octopuses live on the seafloor where they creep
  and scurry about in search of crabs and food.
• Only mollusks with a closed circulatory system.
• Have a well developed nervous system with a
  complex brain. Why?
• Ability to learn and behave in a complex manner
  is more critical to fast moving predators.

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Cephalopod Pics
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Phylum Arthropoda
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General Characteristics

• Arthropoda means jointed feet.
• Nearly one million arthropod species have been
  described, mostly insects.
• Most successful phylum of animals, in all
  habitats. Their success is related to their
  segmentation, hard exoskeleton, and jointed
  appendages.
• All arthropods have the same basic body plan or
  some variation of it. The body is made up of
  three segments the head, thorax, and abdomen.

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• The body of an arthropod is completely covered by
  a cuticle, an exoskeleton made up of protein and
  chitin. Exoskeleton can be modified into thick
  hard armor or paper thin and flexible.
• One Problem. In order to grow an arthropod must
  shed its old exoskeleton and secrete a larger
  one. This process is called molting and it takes
  a lot of energy and leaves the animal
  temporarily vulnerable to its environment.
• The first arthropods appeared in the sea 600
  million years ago. Since arthropods have moved
  to all habitats. They have evolved specialized
  appendages for feeding, movement and other
  functions.

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• Arthropods tune into their environment with well
  developed sensory organs including eyes (simple
  and compound), olfactory receptors for smell, and
  antennae for touch and smell. Cephalization is
  extensive.
• Arthropods have an open circulatory system where
  fluid called hemolymph is pumped by the heart
  through short arteries and then into spaces
  surrounding organs and tissues.
• Terrestrial arthropods have a tracheal system
  which consist of open tubes that connect to the
  outside by spiracles (pores in the cuticle).

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Classification

• Arthropods are classified based on the number and
  structure of their body segments and appendages-
  particularly their mouthparts.
• Arthropods are divided into four subphyla
• Trilobitomorpha- trilobites (extinct).
• Chelicerata- spiders, mites ticks, scorpions.
• Uniramia- insects, centipedes, millipedes.
• Crustacea- crabs, lobsters, shrimps, barnacles,
  crayfish etc.

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Trilobites
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Cheliceriformes
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Uniramia
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Crustacea
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Review Questions

• 1. What is the term for an organism which can
  produce both sperm and eggs?
• 2. Why are sponges classified as part of the
  animal kingdom?
• 3. Why is it helpful for an organism to be able
  to reproduce both sexually and asexually?
• 4. How does a jellyfish obtain food?
• 5. How has the digestive system of planaria been
  improved over that of the jellyfish?
• 6. How does an animal in the phylum
  Platyhelminthes obtain oxygen? Why is this
  sufficient for these organisms?
• 7. A tapeworm is a parasite that lives in the
  intestines of its host. What system would you
  expect to be missing from the tapeworm that would
  be found in other flatworms? By not having this
  system, the tapeworm has created extra space in
  its body. How do you think the worm has used this
  space?
• 8. How have the digestive systems of the
  roundworm and segmented worm been improved
  compared to that of flatworms?
• 9. What is meant by segmentation? How is
  segmentation an evolutionary advantage?
• 10. Some organisms have a circulatory system with
  blood but the blood has no hemoglobin. What is
  the function of the blood in these organisms? Why
  is it an advantage to have hemoglobin in the
  blood?
• 11. How is the annelid coelom different from the
  body cavity of the roundworm.
• 12. Why is a simple circulatory system important
  for the earthworm?
• 13. In a parasitic worm, why would it be useful
  to be hermaphroditic?
• 14. Give a possible reason why bivalves have not
  tended toward cephalization.
• 15. Why have more complex organisms such as
  molluscs had to develop gills?

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• 33. How is the circulatory system of most
  molluscs different from the annelids? Is this
  unexpected?
• 34. Describe feeding in the gastropods, bivalves,
  and cephalopods.
• 35. How are cephalopods different from other
  mollusks?
• 36. Explain how the gills of bivalves perform two
  separate functions?
• 37. How is the closed circulatory system an
  advantage to cephalopods?
• 38. List some characteristics of arthropods.
• 39. Why does the presence of an exoskeleton
  require the presence of jointed appendages?
• 40. Why is molting necessary?
• 41. What are the advantages and disadvantages of
  an exoskeleton?
• 42. What factors limit the size of the insects?