Biology 320Biology 320Invertebrate ZoologyInvertebrate Zoology

Fall 2005Fall 2005

Highlights from Chapter 4 –Highlights from Chapter 4 –

Introduction to MetazoaIntroduction to Metazoa

MetazoansMetazoans

Multicellular organismsMulticellular organisms

Really we are referring Really we are referring to members of to members of Kingdom Animalia, or Kingdom Animalia, or animalsanimals

Believed to have Believed to have evolved from evolved from protozoans; specifically protozoans; specifically choanoflagellateschoanoflagellates

Basic PropertiesBasic Properties EukaryoticEukaryotic

Typically large Typically large Many costs / benefits associated with increased Many costs / benefits associated with increased

size size

MotileMotile Usually even to some degree in sessile animalsUsually even to some degree in sessile animals Many have dual life stages – motile larvae and Many have dual life stages – motile larvae and

sessile adultssessile adults

PolarityPolarity Anterior – posteriorAnterior – posterior Oral - aboralOral - aboral

OntogenyOntogeny

Means “origin of being”Means “origin of being”

Fancy way of saying developmentFancy way of saying development

Zygote formed by union of egg and sperm nucleiZygote formed by union of egg and sperm nuclei

Soon after multicellular embryo is formed in Soon after multicellular embryo is formed in process known as cleavage (division)process known as cleavage (division)

One important, early stage is known as a blastulaOne important, early stage is known as a blastula Hollow ball of cellsHollow ball of cells

Cleavage in a Sea Urchin EmbryoCleavage in a Sea Urchin Embryo

Soon after, one wall of the Soon after, one wall of the blastula invaginatesblastula invaginates Process known as gastrulationProcess known as gastrulation Altered embryo is referred to as a Altered embryo is referred to as a

gastrulagastrula

In most individuals, primary In most individuals, primary germ layers are established germ layers are established by grastrulationby grastrulation Ectoderm – outer layerEctoderm – outer layer Endoderm – inner layerEndoderm – inner layer Mesoderm – middle layerMesoderm – middle layer

Organisms possessing Organisms possessing ectoderm and endoderm are ectoderm and endoderm are said to be diploblasticsaid to be diploblastic

Organisms possessing all Organisms possessing all three germ layers are three germ layers are triploblastictriploblastic

If there is indirect If there is indirect development, a larva development, a larva formsforms Lives independently of Lives independently of

adultadult Very different from Very different from

adultadult Occupies different Occupies different

ecological nicheecological niche

Producing larvae that Producing larvae that occupy a different occupy a different niche allows for niche allows for resource partitioningresource partitioning Example: caterpillar to Example: caterpillar to

butterflybutterfly

Eventually undergoes Eventually undergoes metamorphosis to metamorphosis to become a juvenilebecome a juvenile

Some undergo direct Some undergo direct developmentdevelopment No larval phaseNo larval phase

Juvenile looks just like a Juvenile looks just like a miniature adultminiature adult Example: GrasshoppersExample: Grasshoppers

Believed to be a derived Believed to be a derived trait rather than trait rather than primitiveprimitive

Cells, Tissues, and Cells, Tissues, and SkeletonsSkeletons

Remember, protozoans posses very little cellular Remember, protozoans posses very little cellular specializationspecialization

Most protozoans rely on organelles to carry out all Most protozoans rely on organelles to carry out all cellular functionscellular functions

Different tissue types allow for a partitioning of Different tissue types allow for a partitioning of laborlabor

Damaged or destroyed cells can be regenerated, Damaged or destroyed cells can be regenerated, however if a however if a ParameciumParamecium is badly damaged, the is badly damaged, the whole organism dieswhole organism dies

Some metazoans lack true tissuesSome metazoans lack true tissues

Main tissue types present in early metazoans are Main tissue types present in early metazoans are derived from ectoderm and endodermderived from ectoderm and endoderm Epithelial tissue – line and cover body surfaces and organsEpithelial tissue – line and cover body surfaces and organs Connective tissue – most common and widely distributed Connective tissue – most common and widely distributed

primary tissue type. Consists of cells in an extracellular primary tissue type. Consists of cells in an extracellular matrix (almost always containing collagen fibers)matrix (almost always containing collagen fibers)

Functional Consequences of Body Functional Consequences of Body SizeSize

On average, metazoans range in size from 0.5mm On average, metazoans range in size from 0.5mm to approximately one meterto approximately one meter

Surface area to volume ratio (SA:vol) is drastically Surface area to volume ratio (SA:vol) is drastically affected by an increase in body sizeaffected by an increase in body size Area is squaredArea is squared Volume is cubedVolume is cubed

Body size is negatively correlated with SA:volBody size is negatively correlated with SA:vol

This effects the exchange of substance such as This effects the exchange of substance such as gases, nutrients and wastesgases, nutrients and wastes

However, some However, some metazoans have metazoans have structural adaptations structural adaptations to increase SA:volto increase SA:vol

MicrovilliMicrovilli

PseudopodiaPseudopodia

Tissues arranged in Tissues arranged in sheets with sheets with metabolically inert ECM metabolically inert ECM betweenbetween

Vermiform or flat body Vermiform or flat body planplan

Body plans with fractal Body plans with fractal relationships – example: relationships – example: tubes in sponges tubes in sponges

Rates of diffusion slow Rates of diffusion slow drastically over great drastically over great distancesdistances

Effective diffusion distance Effective diffusion distance is approximately 0.5mm is approximately 0.5mm for most animalsfor most animals

Body diameters of greater Body diameters of greater than 1.0mm may be than 1.0mm may be diffusion-limiteddiffusion-limited

Some animals such as Some animals such as flatworms carry out all gas flatworms carry out all gas exchange via simple exchange via simple diffusion, but others diffusion, but others require a circulatory require a circulatory systemsystem

Generally, metabolic rates are positively Generally, metabolic rates are positively correlated with body sizecorrelated with body size

However, 1g of shrew tissue consumes more However, 1g of shrew tissue consumes more power than 1g of elephant tissuepower than 1g of elephant tissue

Poikilotherms (cold blooded animals) consume 8 Poikilotherms (cold blooded animals) consume 8 times more mass-specific energy than protozoanstimes more mass-specific energy than protozoans

Homeotherms (mammals and birds) consume 29 Homeotherms (mammals and birds) consume 29 times the power of a poikilotherm of equal masstimes the power of a poikilotherm of equal mass

Possessing a circulatory system, and maintaining Possessing a circulatory system, and maintaining a constant body temperature are both a constant body temperature are both metabolically expensivemetabolically expensive

Possible Advantages of Larger Body Possible Advantages of Larger Body SizeSize

Mass-specific decrease in Mass-specific decrease in metabolic ratemetabolic rate

Less danger of predation Less danger of predation by protozoaby protozoa

Predation upon protozoans Predation upon protozoans by metazoansby metazoans

Motile metazoans move at Motile metazoans move at greater speeds that greater speeds that protozoansprotozoans

Multicellularity provides Multicellularity provides the ability to regeneratethe ability to regenerate

Origins of MetazoansOrigins of Metazoans

Colonial theoryColonial theory Metazoa is derived from colonial flagellated protozoansMetazoa is derived from colonial flagellated protozoans Supported by morphological and molecular dataSupported by morphological and molecular data Accepted by the authors of your textAccepted by the authors of your text

rRNA data indicated that Volvox evolved 50 to rRNA data indicated that Volvox evolved 50 to 75mya and is not an ancestor to metazoans 75mya and is not an ancestor to metazoans (believed to have evolved 600mya)(believed to have evolved 600mya)

Choanoflagellates are believed to be the sister Choanoflagellates are believed to be the sister taxontaxon