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