Post on 11-May-2015
Introduction to Animal Evolution
Chapter 32
General Features of Animals
Heterotrophs MobilityMulticellularityDiploidySexual ReproductionAbsence of cell wallBlastula FormationTissues
Animals probably evolved from colonial protists: A choanoflagellate colony
One hypothesis for the origin of animals from a flagellated protist
Heterotrophs
Animals cannot make their own food
Mobility
Animals can perform rapid, complex movements
Multicellularity
All animals are multicellular
Diploidy
Most animals are diploid.
Sexual Reproduction
Most animals reproduce sexually by producing gametes.
Absence of a Cell Wall
Animals lack rigid cell walls.
Blastula Formation
The zygote divides and forms a hollow ball of cells.
Early Embryonic Development
Protostomes & Deuterostomes
Body Cavity
Three types of bodyplans:
Acoelomate – no body cavity
Pseudocoelomate – partial body cavity
Coelomate – body cavity
Body Symmetry
Radial Symmetry – Parts arranged around a central axis.
Bilateral – Right and left half.
Asymmetrical – No symmetry
Tissues & Organs
Cells are organized by structure and function into:
Tissues – groups of cellsMuscle tissue, blood, connective tissue
Organs – groups of tissuesHeart, Lungs, Liver
Origin of Tissues
Segmentation
Advanced animals are segmented.
A traditional view of animal diversity based on body-plan grades
Animal phylogeny based on sequencing of SSU-rRNA
Comparing the molecular based and grade-based trees of animal phylogeny
Cambrian Explosion
Many phyla evolved rapidly over a 40 million year period
Produced high diversity
Makes sorting out phylogenetic tree difficult
Burgess Shale fossils
“Evo-Devo”: Reasons for Cambrian Diversification
Ecological Emergence of predator-prey relationshipsEvolution of protective outer covering & other
adaptationsGeological
Enough atmospheric oxygen to support metabolism
GeneticHox genes- spatial and temporal expression in
developing embryos
InvertebratesChapter 33
Review of animal phylogeny
Phylum Porifera: Sponges
Phylum Porifera
Phylum Cnidaria
Radial symmetry
Gastrovascular cavity
Cnidocytes
A cnidocyte of a hydra
Polyp & Medusa Forms
The life cycle of the hydrozoan Obelia
Classes of Phylum Cnidaria
Cnidarians: Hydrozoans (top left), jelly (top right), sea anemone (bottom left), coral polyps (bottom right)
Phylum Cnetophora
“Comb jellies”
8 rows of cilia
Retractable tentaclesCapture food
Platyhelminthes
Bilateral symmetry
Acoelomate
Organs
Three groups:Turbellaria - flatwormsCestoda - tapewormsTrematoda - flukes
Flatworms•Planarians•Marine flatworms
Marine flatworm
Planarian
Anatomy of a planarian
Tapeworms: absorb nutrients from host
• Flukes - parasitic flatworms
Phylum Rotifera
Pseudocoelomates
Jaws
Crowns of cilia
Complete digestive tract
Lophophorate Phyla Coelomates with ciliated tentacles around their mouths Lophophore: horseshoe or round shaped fold of the body wall
bearing ciliated tentacles
Bryozoans Brachiopods
Phylum Mollusca
3 Body parts:Visceral massMantleFoot
CoelomBilateral symmetryWell-developed
organsRadula – for feedingExoskeleton - shell
Gastropods
Bivalves
Cephalopods
Basic body plan of mollusks
Phylum Annelida
SegmentedMetanephridiaCoelomateRespire through skinClosed circulatory
system3 Classes
OligochaetaPolychaetaHirudinea
PseudoceolomateNon-segmentedCovered by cuticleOne-way gutSimple circulatory &
gas-exchange systems
Parasitic
Phylum Nematoda - Roundworms
Arthropods Jointed appendages Coelomate Segmented Exoskeleton
Classes Arachnida
Spiders, scorpions, mites Diplopoda
Millipedes Chilopoda
centipedes Insecta
insects Crustacea
Crabs, lobsters, crayfish, shrimp
Most diverse animal group
External anatomy of an arthropod
Anatomy of a grasshopper, an insect
Three hypotheses for the origin of segmentation
Purple bars – origins of segmentationOrange bars – loss of segmentation
Phylum Echinodermata
DeuterostomesLack head or brainRadial symmetryCoelomeEndoskeletonWater vascular
system
Ophiuroidea: Brittle Star
Asteroidea: Sea Star
Echinoidea: Sea Urchin
Echinoidea: Sand dollar
Holothuroidea: Sea cucumber
Anatomy of a sea star
Invertebrate Chordates
4 Characteristics of Chordates:NotochordDorsal nerve chordPharangeal slitsPostanal tail
Invertebrate ChordatesUrochordata - tunicatesCephalochordata - lancelets
Tunicates
Lancelets