Chapter 23 Invertebrate Diversity

1
Chapter 23Invertebrate Diversity

• Section 1 Diverse animals share several key
  characteristics
• Section 2 Sponges are relatively simple animals
  with porous bodies
• Section 3 Cnidarians are radial animals with
  stinging cells
• Section 4 Flatworms are the simplest bilateral
  animals
• Section 5 Roundworms and rotifers have complete
  digestive tracts
• Section 6 Annelida are segmented worms
• Section 7 Mollusks show diverse variations on a
  common body form
• Section 8 Echinoderms have spiny skin and a
  water vascular system
• Section 9 Animal diversity exploded during
  the Cambrian period

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The Body of a Flatworm

• Flatworms (phylum Platyhelminthes) are
  bilaterally symmetrical.
• Definition member of a group of small, leaflike
  or ribbonlike invertebrates that includes
  planarians
• Definition body plan in which an animal can be
  divided into two equal sides
• Flatworms have mirror-image left and right sides,
  a distinct head (anterior end), a distinct tail
  (posterior end), a back side (dorsal), a bottom
  side (ventral), and two side surfaces (lateral).
• Flatworms are the simplest animals to have three
  tissue layers the ectoderm, mesoderm, and
  endoderm.

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• During an animals early development
• THE ECTODERM develops into the body covering.
• THE MESODERM develops into an internal
  tissue-filled region.
• THE ENDODERM develops into the digestive sac.
• Similar to cnidarians, flatworms have a digestive
  cavity food enters and wastes exit from one
  opening located on the ventral surface.
• When the animal is feeding, a muscular tube
  projects through the mouth and sucks in food.

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• Flatworms can move in several ways
• They use cilia on its ventral surface to slide
  about in search for food.
• They have muscles that enable it to twist and
  turn.
• Flatworms are aware of their surroundings by
• the pair of eyespots that detect light.
• the side flaps that function mainly for smell.
• The Diversity of Flatworms
• The 20,000 known species are divided into three
  classes
• Class Turbellaria mostly free-living and marine
  (planarians)
• Class Trematoda parasites that absorb nutrients
  from the body fluids of a living host (blood
  fluke)
• Class Cestoidea parasites that live in the
  digestive tracts of vertebrates (tapeworms)

5
Chapter 23Invertebrate Diversity

• Section 1 Diverse animals share several key
  characteristics
• Section 2 Sponges are relatively simple animals
  with porous bodies
• Section 3 Cnidarians are radial animals with
  stinging cells
• Section 4 Flatworms are the simplest bilateral
  animals
• Section 5 Roundworms and rotifers have complete
  digestive tracts
• Section 6 Annelida are segmented worms
• Section 7 Mollusks show diverse variations on a
  common body form
• Section 8 Echinoderms have spiny skin and a
  water vascular system
• Section 9 Animal diversity exploded during
  the Cambrian period

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The Body of a Roundworm

• Most roundworms, or nematodes (phylum Nematoda),
  range in length from less than 1 mm to more than
  7 meters.
• Definition member of a group of cylindrical
  invertebrates with pointed heads and tapered
  tails
• The largest roundworms are parasites found in
  whales.
• Like flatworms, roundworms have three tissue
  layers.
• One characteristic that makes roundworms (and
  annelids) different from flatworms (and
  cnidarians) is the presence of a complete
  digestive tract.
• Definition continuous digestive tube with a
  separate mouth and anus

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• In animals with a digestive tract, the anterior
  region of the tract churns and mixes food with
  enzymes for digestion the posterior region
  absorbs nutrients from the digested food and
  disposes of wastes.
• The Diversity of Roundworms
• Roundworms are among the most numerous on Earth,
  totaling about 15,000 known species.

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• Roundworms live almost every place there is
  rotting organic matter and play a roles as
  important decomposers on the bottom of lakes and
  oceans.
• Other roundworms thrive as parasites in the moist
  tissues of plants and in the body fluids and
  tissues of animals.
• Free-living roundworms (non-parasitic) roundworms
  are the most abundant.
• Many species of parasitic roundworms attack the
  roots of plants and tissues of animals humans
  can be hosts to at least 50 species of roundworms
  parasites.
• One disease that can affect humans is called
  trichinosis ? humans acquire this disease by
  eating undercooked pork or other meat that is
  infected with worms.
• Roundworm parasites of animals are known by
  several common names such as hookworm, pinworm,
  and threadworm (names based on worms appearance).

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Chapter 23Invertebrate Diversity

• Section 1 Diverse animals share several key
  characteristics
• Section 2 Sponges are relatively simple animals
  with porous bodies
• Section 3 Cnidarians are radial animals with
  stinging cells
• Section 4 Flatworms are the simplest bilateral
  animals
• Section 5 Roundworms and rotifers have complete
  digestive tracts
• Section 6 Annelida are segmented worms
• Section 7 Mollusks show diverse variations on a
  common body form
• Section 8 Echinoderms have spiny skin and a
  water vascular system
• Section 9 Animal diversity exploded during
  the Cambrian period

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The Body of an Annelid

• Earthworms and other segmented worms (phylum
  annelida) are called annelids.
• Definition segmented worm
• Annelida ? little rings
• Segmentation is an advantage because each segment
  has its own muscles, allowing shortening and
  lengthening of the body for movement.
• Within each segment is a dense cluster of nerve
  cells and waste-excreting organs.
• Annelids have a distinct head and tail and its
  body segments are all very similar.
• The digestive tract is not segmented and runs the
  length of the animal, along with the nerve cord
  and two main blood vessels.

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• FIGURE 23-12
• Annelids have a closed circulatory system.
• Definition blood transport system in which blood
  remains enclosed in vessels nutrients, oxygen,
  and wastes diffuse through vessel walls
• On the underside of a
• segmented worm are bristles
• these bristles aid in movement.
• FIGURE 23-15

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• Annelids are bilaterally symmetrical and have
  three tissue layers.
• Bilateral symmetry ? when divided in half, it is
  identical on both sides (mirror image)
• The tissue layers are organized differently in
  each of the three groups of worms.
• FLATWORMS are examples of acoelomates.
• Definition animal lacking a body cavity
• ROUNDWORMS each have a pseudocoelom.
• Definition fluid-filled internal space that is
  in direct contact with the wall of the digestive
  tract
• ANNELIDS each have a coelom.
• Definition fluid-filled body cavity completely
  lined by a layer of mesoderm cells

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The Habitat of Annelids

• Segmented worms live in the soil, fresh water,
  and the sea everywhere except frozen soil and
  dry sand.
• The soil is the worms main source of oxygen it
  diffuses into the earthworm through the skin.
• DURING THE DAY The cool, moist soil provides
  protection for the worm.
• AT NIGHT They come to the surface and stay close
  to their burrows.
• The Reproduction of Annelids
• Segmented worms are hermaphrodites (bodies
  contain male and female sex organs).
• During mating, two worms exchange sperm ? the
  sperm fertilizes the eggs contained in the bodies
  of each worm ? the fertilized eggs are expelled
  in the soil ? two-three weeks later, worms hatch
  from the eggs.

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The Diversity of Annelids

• There are about 15,000 known species of annelids,
  grouped into three classes.
• Class Polychaeta includes species that scavenge
  for food on the ocean floor (sandworms)
• Class Oligochaeta includes species who tunnel
  through the soil helping air to circulate in it
  (earthworms)
• Class Hirudinea includes parasitic leeches