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Chapter 23 Invertebrate 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

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chapter 23 invertebrate diversity

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

the body of a flatworm
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.
slide3
During an animal’s 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.
slide4
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)
chapter 23 invertebrate diversity1

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

the body of a roundworm
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
slide7
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.
slide8
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 worm’s appearance).
chapter 23 invertebrate diversity2

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

the body of an annelid
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 it’s 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.
slide11
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

slide12
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
      • ROUNDWORMSeachhave 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
the habitat of annelids
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.
the diversity of annelids
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