Comparing Invertebrates Chapter 29. Invertebrate Evolution Chapter 29-1

Comparing Invertebrates

Chapter 29

Invertebrate Evolution

Chapter 29-1

Origins of InvertebratesOrigins of Invertebrates

Early animals were flat, soft bodied organisms that Early animals were flat, soft bodied organisms that lived on the bottom of shallow seas.lived on the bottom of shallow seas.• Segmented with bilateral symmetry.Segmented with bilateral symmetry.

• NO cell specialization.NO cell specialization.

Recently scientists discovered microscopic fossils Recently scientists discovered microscopic fossils that are 610-570 million years old.that are 610-570 million years old.• Seem to be developing embryos of early multi-cellular Seem to be developing embryos of early multi-cellular

organisms.organisms.

29-1 Invertebrate Evolution

Ediacaran Fossils found in China 610 to 570 Million Years old They are the ancestors of today’s

multicellular animals

The First Multicellular Animals


The First Multicellular Animals

The fossils:• were flat and plate shaped

• were segmented

• had bilateral symmetry

• lived on the bottom of shallow seas

• were made of soft tissues

• absorbed nutrients from the surrounding water


Many features of modern invertebrates evolved during the Cambrian period such as:• tissues and organs

• patterns of early development

• body symmetry

• cephalization

• segmentation

• formation of three germ layers and a coelom

Invertebrate Phylogeny


Invertebrate Evolutionary Relationships



Unicellular ancestor

Sponges

Cnidarians

Flatworms

Roundworms







Invertebrate Evolutionary Relationships



Evolutionary TrendsEvolutionary Trends

Specialized cells, Tissues, and OrgansSpecialized cells, Tissues, and Organs

•Sponges - 1Sponges - 1stst with specialized cells with specialized cells

•Jelly fish - 1Jelly fish - 1stst with muscle tissue with muscle tissue

•Flatworms - 1Flatworms - 1stst with organs with organs

Body SymmetryBody Symmetry

•Asymmetrical (no symmetry) – Sponges Asymmetrical (no symmetry) – Sponges onlyonly

•Radial – Jellyfish and EchinodermsRadial – Jellyfish and Echinoderms

•Bilateral – Flatworms, Roundworms, Bilateral – Flatworms, Roundworms, Annelids, arthropods, and MollusksAnnelids, arthropods, and Mollusks


• Cnidarians and echinoderms exhibit radial symmetry where parts extend from the center of the body.

Radial symmetry

Planes of symmetry

Evolutionary TrendsEvolutionary Trends29-1 Invertebrate Evolution

Bilateral symmetry

• Worms, mollusks, and arthropods exhibit bilateral symmetry, or have mirror-image left and right sides.


Cephalization Cephalization

• Cephalization is the concentration of sense organs and nerve cells in the front of the body.

• Invertebrates with cephalization can respond to the environment in more sophisticated ways than can simpler invertebrates.

• None: SpongesNone: Sponges• Nerve Net: CnidariansNerve Net: Cnidarians• Ganglia: Worms, Clams, EchinodermsGanglia: Worms, Clams, Echinoderms• Brains: Cephalopod Mollusks, ArthropodsBrains: Cephalopod Mollusks, Arthropods


SegmentationSegmentation• Over the course of evolution, different

segments in invertebrates have often become specialized for specific functions.

• Segmentation allows an animal to increase its size with minimal new genetic material.


•Coelom FormationCoelom Formation • Flatworms are acoelomates. This means they have no

coelom, or body cavity, that forms between the germ layers.

Digestive cavity

Acoelomate

Ectoderm Mesoderm Endoderm


Pseudocoelomate

Pseudocoelom

Digestive tract

Pseudocoelomates have a body cavity lined partially with mesoderm.


• Most complex animal phyla have a true coelom that is lined completely with tissue derived from mesoderm.

Coelom

Digestive tract

Coelomate



•Embryological Development Embryological Development • In most invertebrates, the zygote divides to form a

blastula—a hollow ball of cells.


In most worms and arthropods, nerve cells are arranged in structures called ganglia.

In more complex invertebrates, nerve cells form an organ called a brain.




Invertebrate Form & Function

Chapter 29-2

The End

Feeding and DigestionFeeding and Digestion

IntraIntracellularcellular: Food digested : Food digested by cells and passed around by cells and passed around by diffusion. (ex: sea by diffusion. (ex: sea anemone)anemone)

• ExtraExtracellularcellular: food: food broken down in broken down in cavity and then cavity and then absorbed. (ex: absorbed. (ex: earthworm)earthworm)

29-2 Form and Function in Invertebrates

Feeding and Digestion• The simplest animals break down food

primarily through intracellular digestion. More complex animals use extracellular digestion.

Feeding and DigestionFeeding and Digestion29-2 Form and Function in Invertebrates

When food is digested inside cells, this process is known as intracellular digestion.

Sponges use intracellular digestion.


In extracellular digestion, food is broken down outside the cells in a digestive cavity or tract and then absorbed into the body.

Mollusks, annelids, arthropods, and echinoderms rely almost entirely on extracellular digestion.

Flatworms and cnidarians use both intracellular and extracellular digestion.


Cnidarians and most flatworms ingest food and expel wastes through a single opening.

Food is digested in a cavity through both extracellular and intracellular means.


Mouth/anus

Digestive cavity

Gastrovascular cavity

Pharynx

Mouth/anus

Cnidarian

Flatworm


In more-complex animals, food enters the mouth and wastes leave through the anus.

A one-way digestive tract often has specialized regions.


Intestine

Gizzard

Crop

Pharynx

MouthAnnelid

Anus

Stomach and digestive glands

Arthropod

PharynxCrop

Intestine

Rectum

Anus

Mouth

Feeding andFeeding and DigestionDigestion


• All respiratory systems have two basic requirements:

• a large surface area that is in contact with the air or water

• the respiratory surfaces must be moist for diffusion to occur

RespirationRespiration29-2 Form and Function in Invertebrates

Aquatic invertebrates:Aquatic invertebrates:

Require moist respiratory Require moist respiratory surfacessurfaces

Some through the pores Some through the pores of the skin of the skin

Some through gills (large Some through gills (large feathery structure rich in feathery structure rich in blood vessels)blood vessels)



• Gills are feathery structures that expose a large surface area to the water.

• Aquatic Invertebrates

Terrestrial Invertebrates:Terrestrial Invertebrates:

Covered by water or mucus Covered by water or mucus inside the body.inside the body.

Book lungs – spidersBook lungs – spiders

Spiracles - other insectsSpiracles - other insects

Spiracles

Book Lungs


Grasshoppers and other insects have spiracles and tracheal tubes.

RespirationRespiration

• Terrestrial Invertebrates


Most complex animals have one or more hearts to move blood through their bodies and either an open or closed circulatory system

CirculationCirculation29-2 Form and Function in Invertebrates

OpenOpen – blood partially contained in vessels – blood partially contained in vessels

ClosedClosed – blood forced through vessels – blood forced through vessels


• Open Circulatory SystemsOpen Circulatory Systems

• In an open circulatory system, blood is only

partially contained within a system of blood vessels.

• One or more hearts or heartlike organs pump blood through blood vessels into a system of sinuses, or spongy cavities.

• The blood makes its way back to the heart.


Open circulatory systems are characteristic of arthropods and most mollusks.


• Closed Circulatory SystemsClosed Circulatory Systems

• In a closed circulatory system, a heart or heartlike organ forces blood through vessels that extend throughout the body.

• Materials reach body tissues by diffusing across the walls of the blood vessels.

• Closed circulatory systems are characteristic of larger, more active animals.


Among the invertebrates, closed circulatory systems are found in annelids and some mollusks.

Small vessels in tissue

Heartlike structure

Blood vessels

Heartlike structuresAnnelid: Closed Circulatory System


• Most animals have an excretory system that rids the body of metabolic wastes while controlling the amount of water in the tissues.

• In aquatic invertebrates, ammonia diffuses from their body tissues into the surrounding water.

ExcretionExcretion29-2 Form and Function in Invertebrates

Aquatic invertebrates:Aquatic invertebrates:• Diffusion: aquatic mollusks, sponges, and jelly fishDiffusion: aquatic mollusks, sponges, and jelly fish

Mollusk Mollusk examplesexamples

• Flame cells: flatwormsFlame cells: flatworms


Terrestrial InvertebratesTerrestrial Invertebrates• Convert ammonia to urea Convert ammonia to urea

to conserve waterto conserve water

• Nephridia: Terrestrial mollusks Nephridia: Terrestrial mollusks

and earthwormsand earthworms

• Malpighian tubules: insects Malpighian tubules: insects

and spidersand spiders


Flatworms use a network of flame cells to eliminate excess water.

Flame CellsExcretory tubules

Flame Cell

Excretory tubuleFlatworm


In annelids and mollusks, urine forms in tubelike structures called nephridia.

Excretory pore

Nephrostome

Nephridia Annelid


Fluid enters the nephridia through openings called nephrostomes.

Urine leaves the body through excretory pores.

Urine is highly concentrated, so little water is lost.


Some insects and arachnids have Malpighian tubules, saclike organs that convert ammonia into uric acid.

ArthropodMalpighian tubules

Digestive tractExcretionExcretion


Uric acid and digestive wastes combine to form a thick paste that leaves the body through the rectum.

The paste helps to reduce water loss.


•Invertebrates show three trends in the evolution of the nervous system: centralization, cephalization, and specialization.

ResponseResponse29-2 Form and Function in Invertebrates

ResponseResponse Nerve Nets:Nerve Nets: individual nerve cells in a net-like individual nerve cells in a net-like

formation.formation.

Ganglia:Ganglia: Centralized nerve cells connected to the Centralized nerve cells connected to the nerve net.nerve net.

Brain:Brain: Highly organized ganglia connected to Highly organized ganglia connected to nerve net.nerve net.

Specialization:Specialization: when cells have a special job (ex: when cells have a special job (ex: eyespots, eyes, chemical receptors, etc.)eyespots, eyes, chemical receptors, etc.)


• Centralization and CephalizationCentralization and Cephalization

• Cephalization is the concentration of nerve tissue and organs in one end of the body.


• SpecializationSpecialization

• The more complex an animal’s nervous system is, the more developed its sense organs tend to be.

• Complex animals may have a variety of specialized sense organs that detect light, sound, chemicals, movement, and electricity.


Cnidarians have nerve nets which consist of individual nerve cells that form a netlike arrangement throughout the animal’s body.

Nerve cells

Cnidarian


In flatworms and roundworms, the nerve cells are more centralized.

There are a few clumps of nerve tissue, or ganglia, in the head.

Ganglia

Flatworm


In cephalopod mollusks and arthropods, ganglia are organized into a brain.

Brain

Mollusk

ArthropodGanglia

Brain


Most animals use muscles to move, breathe, pump blood, and perform other life functions.

In most animals, muscles work together with some sort of skeletal system that provides firm support.

Movement and SupportMovement and Support


Movement and SupportMovement and Support

Hydrostatic skeleton:Hydrostatic skeleton: muscles surround muscles surround a fluid-filled body cavity. a fluid-filled body cavity.

Exoskeleton:Exoskeleton: Arthropods: Hard body Arthropods: Hard body covering made of chitin.covering made of chitin.

Endoskeleton:Endoskeleton: Echinoderms: internal Echinoderms: internal structural support.structural support.


Movement and Support

Water

Water

Circular muscles contracted

Longitudinal muscles contracted

• Hydrostatic Hydrostatic SkeletonSkeleton


Extended joint

Flexed joint • ExoskeletonExoskeleton



• EndoskeletonEndoskeleton

Tube foot

Skeletal plates



Sexual reproductionSexual reproduction maintains genetic diversity in a population.

Asexual reproductionAsexual reproduction allows animals to reproduce rapidly and take advantage of favorable conditions in the environment.

Sexual & Asexual ReproductionSexual & Asexual Reproduction


Sexual reproduction is the production of offspring from the fusion of gametes.

Male and female gametes join to create a zygote.

The zygote grows through mitosis and develops into a multicellular animal.



In most animals, each individual is a single sex. (male of female)

The individual produces either sperm or eggs.

Some animals are hermaphrodites—individuals that produce both sperm and eggs.



In external fertilization, eggs are fertilized outside the female’s body.

In internal fertilization, eggs are fertilized inside the female’s body.



The offspring of asexual reproduction grow into multicellular organisms by mitosis of diploid cells.

Some animals reproduce asexually through budding or by dividing in two.



ReproductionReproduction

Most invertebrate reproduce sexually Most invertebrate reproduce sexually to increase genetic diversity.to increase genetic diversity.

BUT….in certain conditions they will BUT….in certain conditions they will reproduce asexually in order to reproduce asexually in order to ensure continuation of species.ensure continuation of species.


Documents

Comparing Invertebrates Chapter 29. Invertebrate Evolution Chapter 29-1