Chapter 23Chapter 23Invertebrate DiversityInvertebrate Diversity

Section 1 –Section 1 – Diverse animals share several key Diverse animals share several key characteristicscharacteristics

Section 2 –Section 2 – Sponges are relatively simple animals with Sponges are relatively simple animals with porous porous bodiesbodiesSection 3 –Section 3 – Cnidarians are radial animals with stinging Cnidarians are radial animals with stinging cellscellsSection 4 –Section 4 – Flatworms are the simplest bilateral animalsFlatworms are the simplest bilateral animalsSection 5 –Section 5 – Roundworms and rotifers have complete Roundworms and rotifers have complete digestive digestive tractstractsSection 6 –Section 6 – Annelida are segmented wormsAnnelida are segmented wormsSection 7 –Section 7 – Mollusks show diverse variations on a Mollusks show diverse variations on a common common body formbody formSection 8 – Section 8 – Echinoderms have spiny skin and a water Echinoderms have spiny skin and a water vascular vascular systemsystemSection 9 –Section 9 – Animal diversity “exploded” during the Animal diversity “exploded” during the Cambrian Cambrian periodperiod

The Body of a FlatwormThe Body of a Flatworm FlatwormsFlatworms ( (phylum Platyhelminthesphylum Platyhelminthes) are ) are

bilaterally symmetricalbilaterally symmetrical.. DefinitionDefinition: member of a group of small, leaflike or : member of a group of small, leaflike or

ribbonlike invertebrates that includes planarians ribbonlike invertebrates that includes planarians DefinitionDefinition: body plan in which an animal can be : body plan in which an animal can be

divided into two equal sides divided into two equal sides Flatworms have mirror-image left and right sides, a Flatworms have mirror-image left and right sides, a

distinct head (distinct head (anterior endanterior end), a distinct tail ), a distinct tail ((posterior endposterior end), a back side (), a back side (dorsaldorsal), a bottom side ), a bottom side ((ventralventral), and two side surfaces (), and two side surfaces (laterallateral).).

Flatworms are the simplest animals to have Flatworms are the simplest animals to have three tissue layersthree tissue layers: : the ectodermthe ectoderm, , mesodermmesoderm, and , and endodermendoderm..

During an animal’s early development:During an animal’s early development: THE ECTODERMTHE ECTODERM: develops into the body : develops into the body

covering.covering. THE MESODERMTHE MESODERM: develops into an internal : develops into an internal

tissue-filled region.tissue-filled region. THE ENDODERMTHE ENDODERM: develops into the digestive : develops into the digestive

sac.sac. Similar to cnidarians, flatworms have a Similar to cnidarians, flatworms have a

digestive cavity – digestive cavity – food enters and wastes exit food enters and wastes exit from one opening located on the ventral surface.from one opening located on the ventral surface. When the animal is feeding, a When the animal is feeding, a muscular tubemuscular tube

projects through the mouth and sucks in food.projects through the mouth and sucks in food.

Flatworms can move in several ways:Flatworms can move in several ways: They use cilia on its ventral surface to slide about in They use cilia on its ventral surface to slide about in

search for food.search for food. They have muscles that enable it to twist and turn.They have muscles that enable it to twist and turn.

Flatworms are aware of their surroundings by:Flatworms are aware of their surroundings by: the pair of eyespots that detect light.the pair of eyespots that detect light. the side flaps that function mainly for smell.the side flaps that function mainly for smell.

The Diversity of FlatwormsThe Diversity of Flatworms The 20,000 known species are divided into The 20,000 known species are divided into

three classes:three classes: Class Turbellaria: Class Turbellaria: mostly free-living and marine mostly free-living and marine

((planariansplanarians)) Class Trematoda: Class Trematoda: parasites that absorb nutrients parasites that absorb nutrients

from the body fluids of a living host (from the body fluids of a living host (blood flukeblood fluke)) Class Cestoidea: Class Cestoidea: parasites that live in the digestive parasites that live in the digestive

tracts of vertebrates (tracts of vertebrates (tapewormstapeworms))

Chapter 23Chapter 23Invertebrate DiversityInvertebrate Diversity

Section 1 –Section 1 – Diverse animals share several key Diverse animals share several key characteristicscharacteristics

Section 2 –Section 2 – Sponges are relatively simple animals with Sponges are relatively simple animals with porous porous bodiesbodiesSection 3 –Section 3 – Cnidarians are radial animals with stinging Cnidarians are radial animals with stinging cellscellsSection 4 –Section 4 – Flatworms are the simplest bilateral animalsFlatworms are the simplest bilateral animalsSection 5 –Section 5 – Roundworms and rotifers have complete Roundworms and rotifers have complete digestive digestive tractstractsSection 6 –Section 6 – Annelida are segmented wormsAnnelida are segmented wormsSection 7 –Section 7 – Mollusks show diverse variations on a Mollusks show diverse variations on a common common body formbody formSection 8 – Section 8 – Echinoderms have spiny skin and a water Echinoderms have spiny skin and a water vascular vascular systemsystemSection 9 –Section 9 – Animal diversity “exploded” during the Animal diversity “exploded” during the Cambrian Cambrian periodperiod

The Body of a RoundwormThe Body of a Roundworm Most Most roundwormsroundworms, or nematodes (, or nematodes (phylum phylum

NematodaNematoda), range in length from less than 1 ), range in length from less than 1 mm to more than 7 meters.mm to more than 7 meters.

DefinitionDefinition: member of a group of cylindrical : member of a group of cylindrical invertebrates with pointed heads and tapered invertebrates with pointed heads and tapered tailstails

The largest roundworms are parasites found The largest roundworms are parasites found in whales.in whales.

Like flatworms, roundworms have three tissue Like flatworms, roundworms have three tissue layers.layers.

One characteristic that makes roundworms (One characteristic that makes roundworms (and and

annelidsannelids) different from flatworms () different from flatworms (and cnidariansand cnidarians) ) is the presence of a is the presence of a complete digestive tractcomplete digestive tract..

DefinitionDefinition: continuous digestive tube with a : continuous digestive tube with a separate mouth and anusseparate mouth and anus

In animals with a digestive tract, the anterior In animals with a digestive tract, the anterior region of the tract churns and mixes food region of the tract churns and mixes food with enzymes for digestion – the posterior with enzymes for digestion – the posterior region absorbs nutrients from the digested region absorbs nutrients from the digested food and disposes of wastes.food and disposes of wastes.

The Diversity of RoundwormsThe Diversity of Roundworms Roundworms are among the most numerous Roundworms are among the most numerous

on Earth, totaling about on Earth, totaling about 15,000 15,000 known known species.species.

Roundworms live almost every place there is rotting Roundworms live almost every place there is rotting organic matter and play a roles as important organic matter and play a roles as important decomposers on the bottom of lakes and oceans.decomposers on the bottom of lakes and oceans. Other roundworms thrive as parasites in the moist tissues Other roundworms thrive as parasites in the moist tissues

of plants and in the body fluids and tissues of animals.of plants and in the body fluids and tissues of animals. Free-living roundworms (non-parasitic) roundworms Free-living roundworms (non-parasitic) roundworms

are the most abundant.are the most abundant. Many species of parasitic roundworms attack the Many species of parasitic roundworms attack the

roots of plants and tissues of animals – roots of plants and tissues of animals – humans can humans can be hosts to at least 50 species of roundworms parasites.be hosts to at least 50 species of roundworms parasites. One disease that can affect humans is called trichinosis One disease that can affect humans is called trichinosis

humans acquire this disease by eating undercooked pork humans acquire this disease by eating undercooked pork or other meat that is infected with worms.or other meat that is infected with worms.

Roundworm parasites of animals are known by several Roundworm parasites of animals are known by several common names such as common names such as hookwormhookworm, , pinwormpinworm, and , and threadwormthreadworm (names based on worm’s appearance). (names based on worm’s appearance).

Chapter 23Chapter 23Invertebrate DiversityInvertebrate Diversity

Section 1 –Section 1 – Diverse animals share several key Diverse animals share several key characteristicscharacteristics

Section 2 –Section 2 – Sponges are relatively simple animals with Sponges are relatively simple animals with porous porous bodiesbodiesSection 3 –Section 3 – Cnidarians are radial animals with stinging Cnidarians are radial animals with stinging cellscellsSection 4 –Section 4 – Flatworms are the simplest bilateral animalsFlatworms are the simplest bilateral animalsSection 5 –Section 5 – Roundworms and rotifers have complete Roundworms and rotifers have complete digestive digestive tractstractsSection 6 –Section 6 – Annelida are segmented wormsAnnelida are segmented wormsSection 7 –Section 7 – Mollusks show diverse variations on a Mollusks show diverse variations on a common common body formbody formSection 8 – Section 8 – Echinoderms have spiny skin and a water Echinoderms have spiny skin and a water vascular vascular systemsystemSection 9 –Section 9 – Animal diversity “exploded” during the Animal diversity “exploded” during the Cambrian Cambrian periodperiod

The Body of an AnnelidThe Body of an Annelid Earthworms and other segmented worms Earthworms and other segmented worms

((phylum annelidaphylum annelida) are called ) are called annelidsannelids.. Definition: segmented wormDefinition: segmented worm

AnnelidaAnnelida “ “little ringslittle rings”” Segmentation is an advantage because each Segmentation is an advantage because each

segment has its own muscles, allowing segment has its own muscles, allowing shorteningshortening and and lengtheninglengthening of the body for movement. of the body for movement.

Within each segment is a dense cluster of nerve cells Within each segment is a dense cluster of nerve cells and waste-excreting organs.and waste-excreting organs.

Annelids have a distinct head and tail and it’s Annelids have a distinct head and tail and it’s body segments are all very similar.body segments are all very similar. The The digestive tractdigestive tract is not segmented and runs the is not segmented and runs the

length of the animal, along with the length of the animal, along with the nerve cordnerve cord and and two main blood vesselstwo main blood vessels..

FIGURE 23-12FIGURE 23-12

Annelids have a Annelids have a closed circulatory systemclosed circulatory system.. DefinitionDefinition: blood transport system in which : blood transport system in which

blood remains enclosed in vessels; nutrients, blood remains enclosed in vessels; nutrients, oxygen, and wastes diffuse through vessel walls oxygen, and wastes diffuse through vessel walls

On the underside of aOn the underside of a

segmented worm are bristlessegmented worm are bristles– – these bristles aid in movement.these bristles aid in movement.

FIGURE 23-15FIGURE 23-15

Annelids are bilaterally symmetrical and have Annelids are bilaterally symmetrical and have three tissue layers.three tissue layers. Bilateral symmetry Bilateral symmetry when divided in half, it is when divided in half, it is

identical on both sides (identical on both sides (mirror imagemirror image)) The tissue layers are organized differently in each of The tissue layers are organized differently in each of

the three groups of worms.the three groups of worms.

FLATWORMS FLATWORMS are examples of are examples of acoelomatesacoelomates.. DefinitionDefinition: animal lacking a body cavity: animal lacking a body cavity

ROUNDWORMSROUNDWORMS eacheach have a have a pseudocoelompseudocoelom.. DefinitionDefinition: fluid-filled internal space that is in : fluid-filled internal space that is in

direct contact with the wall of the digestive direct contact with the wall of the digestive tracttract

ANNELIDS ANNELIDS each have a each have a coelomcoelom.. DefinitionDefinition: fluid-filled body cavity completely : fluid-filled body cavity completely

lined by a layer of mesoderm cellslined by a layer of mesoderm cells

The Habitat of AnnelidsThe Habitat of Annelids Segmented worms live in the soil, fresh water, Segmented worms live in the soil, fresh water,

and the sea – and the sea – everywhere except frozen soil and dry everywhere except frozen soil and dry sand.sand. The soil is the worms main source of oxygen – it The soil is the worms main source of oxygen – it

diffuses into the earthworm through the skin.diffuses into the earthworm through the skin. DURING THE DAY:DURING THE DAY: The cool, moist soil provides The cool, moist soil provides

protection for the worm.protection for the worm. AT NIGHT:AT NIGHT: They come to the surface and stay close to They come to the surface and stay close to

their burrows.their burrows.

The Reproduction of AnnelidsThe Reproduction of Annelids Segmented worms are hermaphrodites (Segmented worms are hermaphrodites (bodies bodies

contain male and female sex organscontain male and female sex organs).). During mating, two worms exchange spermDuring mating, two worms exchange sperm the the

sperm fertilizes the eggs contained in the bodies of sperm fertilizes the eggs contained in the bodies of each wormeach worm the fertilized eggs are expelled in the the fertilized eggs are expelled in the soilsoil two-three weeks later, worms hatch from the two-three weeks later, worms hatch from the eggs.eggs.

The Diversity of AnnelidsThe Diversity of Annelids There are about There are about 15,000 known species15,000 known species of of

annelids, grouped into three classes.annelids, grouped into three classes. Class Polychaeta:Class Polychaeta: includes species that includes species that

scavenge for food on the ocean floor scavenge for food on the ocean floor ((sandwormssandworms)) Class Oligochaeta:Class Oligochaeta: includes species who tunnel includes species who tunnel

through the soil helping air to circulate in it through the soil helping air to circulate in it ((earthwormsearthworms))

Class Hirudinea:Class Hirudinea: includes parasitic leechesincludes parasitic leeches