The Wonderful World of Animals!

What is true about ALL animals?

• They are eukaryotic• They are multicellular• They are heterotrophs (If they make their own

food, they are not animals)• They lack cell walls• They possess nervous tissue and muscle (at

least myosin and actin in some form)• Generally, they reproduce sexually

How do we begin to classify animals?

• 1. How many “layers” do they have?• Uniblastic

• Diploblastic: only an endoderm and ectoderm

• Triploblastic: endoderm, mesoderm, ectoderm– Vast majority of animal phyla are triploblastic

How do we begin to classify animals?

• 2. What type of “symmetry” do they have?• Radial symmetry: best for animals that don’t

have to move much…

How do we begin to classify animals?

• Bilateral symmetry: great for animals that need to move fast

• With bilateral symmetry came “cephalization”– The movement of sensory organs and nervous

tissues in a head at the anterior of the animal– Good to have this all up front…it’s what

encounters a new environment 1st

How do we begin to classify animals?

• With bilateral symmetry also came “segmentation”

• Developing a series of ‘body units’ (like an earthworm)

• Allowed animals to develop specialized parts…legs, wings, antennae

How do we begin to classify animals?• 3. What do their body cavities look like?• Coelom: “body cavity”• A. Acoelomate: no body cavity; everything

between body wall and internal organs is filled with mesenchyme

Flatworm

Body Cavities

• B. Pseudocoelomate: mesoderm lines the inside of the body wall but NOT the internal organs

Ascaris: A Parasitic Roundworm

Body Cavities

• C. Coelomate: Both inside body wall and internal organs are lined by mesoderm

• “peritoneum”

Phylum Porifera

• Sponges!– Uniblastic– If any symmetry at all, it is radial– Sessile

Phylum Cnideria• Usually radial symmetry• Diploblastic: Has 2 cell layers: endoderm and

ectoderm• Blind gut: mouth and anus are the same opening• All are carnivores; possess nematocysts• Jellyfish, sea anemones, corals

Ctenophores (Comb Jellies)• Complete guts (separate mouth and anus)• Usually radial symmetry• Diploblastic: Has 2 cell layers: endoderm and

ectoderm• Sticky tentacles, not nematocysts

Protostomes vs. Deuterostomes

• Stome: Mouth• Proto: First• Deutero: Second• Protostome: Mouth forms 1st from

blastopore• Deuterostome: Anus forms 1st from

blastopore, mouth arises elsewhere 2nd

What is a blastopore anyway?

• Spot in the embryo where vegetal pole folds inward

This is a sea urchin embryo…Is it a protosome or a deuterostome?

Comparison/Contrast

Protostomes• Triploblastic• Bilateral symmetry• Cephalized (anterior

brain)• Blastopore becomes

the MOUTH• VENTRAL nervous

system

Deuterostomes• Triploblastic• Bilateral symmetry• Cephalized (anterior

brain)• Blastopore becomes

the ANUS• DORSAL nervous

system

Protostomes (many phyla)

Lophotrochozoans• Grow by adding size• Flatworms

(Platyhelminthes)• Rotifera• Annelids

(Segmented worms)• Mollusks

Ecdysozoans• Grow by molting• Nematodes (cuticles)• Arthropods

(segmented external skeleton)– Crustaceans– Insects– Arachnids

Those who grow by adding size

• Platyhelminths (flatworms)

Those who grow by adding size

• Rotifers

Those who grow by adding size

• Annelids (includes the earthworm)

Circulatory System of an Annelid

• The circulatory system is CLOSED

Blood is enclosed within vessels and does not mix with other body fluids

As you might expect, this is also characteristic of all vertebrates

Those who grow by adding size

• Mollusks• From snails to clams to octopus to giant squid

Body plan of a mollusk

• Visceral mass, mantle, & foot

Circulatory System of a Mollusk

• The circulatory system is OPENArthropods will be like this too.

Blood mixes with other body fluids

Those who grow by molting

• These animals have an “exoskeleton”

• Nematodes (Roundworms)– External cuticle: flexible but unsegmented

• Arthropods: Segmented external skeleton– “Jointed foot”

Arthropods

• Crustaceans• Insects• Arachnids

Crustaceans

• Marine animals• 3 body segments• Head, thorax, and abdomen

Insects

1.4 MILLION species

Arachnids

• Scorpions and spiders

On to Deuterostomes

• Two major classifications• 1. Echinoderms• 2. Chordates

– Characterized by dorsal notochord which becomes the vertebrae in Vertebrates

Echinoderms• Starfish, sand dollars, sea urchines

Chordates

• Features at some point during development– Pharyngeal slits– A dorsal hollow nerve cord– A dorsal supporting rod (notochord)– A tail extending past the anus– A ventral heart

Relationship of Chordates

• We’ll draw a picture here!

How the Circulatory Systems Differ Among the Chordates

Fish

Lungfish

Amphibians

Crocodile

Reptiles

Birds and Mammals