Animal Origins and the Evolution of Body Plans

Animals

• 1. multicellular heterotrophs

• 2. structural proteins

• 3. unique tissues

Animals

• 4. diploid with development proceeding via a blastula

zygote blastula gastrulacleavage gastrulation

Evolutionary Relationships

• monophyletic group

• differences lie in body plans and developmental patterns

Body Plans

• based on symmetry– asymmetric– radial – bilateral

• cephalization is correlated with bilateral symmetry

Body Plans

• Hox cluster– found in all bilaterally symmetrical

animals– determines morphological development

• e.g. genes that determine head development are the same in flatworms and humans

Developmental Differences

• germ layers– endoderm

– mesoderm

– ectoderm

• diploblastic vs. triploblastic

Developmental Differences

• body cavities– acoelomate– pseudocoelomate– coelomate

• protostome• deuterostome

Protostome/Deuterostome Characteristics

Characteristic Protostome Deuterostome

Cleavage Pattern

spiral, determinate

radial, indeterminate

Coelom Formation

schizocoelous enterocoelous

Fate of blastopore

mouth anus

Phylum Porifera

• sessile

• no true tissues

• marine and freshwater

Phylum Porifera

• body plan– two layers separated by

mesohyl• amoebocytes• spicules

– spongocoel– osculum– choanocytes– hermaphrodites

Phylum Cnidaria

• blind gut (gastrovascular cavity)

• sessile polyp, floating medusa

• tentacles with cnidocytes– nematocysts

Phylum Cnidaria

• diploblastic (2 germ layers)– mesoglea

• nerve net

• sexual and asexual reproduction

Phylum Ctenophora

• all marine• 8 rows of comb-like

plates • tentacles with

colloblasts• complete gut

Protostomia vs. Deuterostomia

• bilaterally symmetrical

• protostomes– CNS with brain surrounding entrance to a

digestive tract– ventral nervous system– free floating larva

Protostomia vs. Deuterostomia

• deuterostomes– dorsal nerve system

Phylum Platyhelminthes

• bilateral symmetry• no body cavity• triploblastic• marine and freshwater• free-living and symbiotic

Platyhelminthes

• dorsoventrally flattened– surface area to volume

• gastrovascular cavity

• sexual and asexual reproduction

Class Turbellaria

• majority are free-living– e.g. planarian

• move using cilia • flame cells for water

balance• regeneration• hermaphrodites

Classes Monogenea and Trematoda

• called flukes

• filled with reproductive organs

• mostly parasitic

Class Cestodea

• tapeworms

• all parasitic

• proglottids

Phylum Annelida

• protostome coelomate• segmentation• closed circulatory system• metanephridia• hermaphrodites

– cross fertilize

Class Polychaeta

• mostly marine

• parapodia with setae

Class Oligochaeta

• terrestrial and freshwater

• few setae

• no parapodia

• cutaneous gas exchange

Class Hirudinea

• leeches• freshwater or moist

areas• parasitic or

carnivorous• no setae

Phylum Mollusca

• protostome coelomate• marine and freshwater• open circulatory system• hermaphroditic and dioecious• 3 part body plan

– foot– visceral mass– mantle

Class Polyplacophora

• termed chitons

• 8 dorsal plates

• most are marine herbivores

Class Gastropoda

• marine, freshwater, and terrestrial

• may possess shells

• gills or primitive lung

Class Bivalvia

• divided shells hinged

• gills for feeding and gas exchange

Class Cephalopoda

• carnivorous, marine• modified foot

– tentacles and part of head

• move via propulsion of water from mantle• closed circulatory system• complex brain