biology 320 invertebrate zoology fall 2005 highlights from chapter 4 – introduction to metazoa
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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