Animal Phyla

It all started with the tiny little ancestral protist.

First evolutionary milestone:

Multicellularity!! First multicellular animal

was probably the…..

Phylum: Porifera

Multicellular

Lack “true” tissues

Sponges

Phylum: Cnidarians Next evolutionary milestone:

– TRUE TISSUES!!! Diploblastic (2 tissue layers):

– Ectoderm & Endoderm Polyps (sea anemones) or

medusas (jellyfish) Radial Symmetry: symmetry

around a central axis Examples: hydras, jellyfish,

coral

Phylum: Platyhelminthes Evolutionary Milestone: Triploblastic (3 tissue layers):

– Ectoderm– Mesoderm– Endoderm

Bilateral Symmetry Acoelomate – without body

cavity Cephalization: sense organs at

the anterior end Examples: flatworms - planaria,

tapeworms, flukes

Phylum: Nematoda

Evolutionary Milestone: A space between the tissues

called a: “Coelum” but….. Nematodes are acually:

“Pseudocoelomates”– Cavity is just between the 2

tissue layers.

Examples: – roundworms – pinworms, hookworms

Protostome vs Deuterostome?This next step isn’t really a “milestone,

… it’s more like a “fork in the river”.

The next several Phyla are all protostomes…..

Protostome- Coelom originates from a cell mass.

Deuterostome- Coelom originates from a digestive tube.

Blastopore: the first opening into embryo, it will become mouth in protosomes and the anus in deuterosomes.

First Protostome: Phylum: MolluscaA true coelom!

(albeit reduced)

Soft bodied animals (slugs, clams, snails, squids, octopuses

3 main body parts – muscular foot, visceral mass, mantle

Hard shells made of calcium carbonate

Organs not really compartmentalized.

Phylum: Annelids Evolutionary milestones: Segmentation!

– Allows for more compartmentalization and specialization

Also a true coelom! – A split within the mesoderm

provides “mesentaries” from which organs can suspend.

Segmented worms (earthworms, leeches)

(also have a closed circulatory system…. More about that to come…)

Phylum:Arthropods Evolutionary Milestone: Jointed Appendages!! Insects, arachnids,

millipedes, centipedes, crustaceans

Reminders:– Arthropods (as well as

annalids) are segmented.– We are still on the branch of

protostomes.

…but now let’s go back to the dueterostome branch:

First Deuterostome:

Phylum: EchinodermataSea stars and sea urchins

Coelomates with secondary radial anatomy– Larvae: bilateral– Adults: radial

Water vascular system used for moving, feeding, and gas exchange

Actually have a type of internal skeleton.

This leads us to our last Phylum:

Phylum: Chordata Lancelets, tunicates,

vertebrates Coelomates with

notochord Dorsal, hollow nerve cord Hagfish Chondrichthyes (Sharks/Rays) Osteichthyes (Bony Fish) Amphibians (Frogs, Salamanders) Reptiles (Snakes, Turtles, Crocs) Aves (Birds) Mammals

– (Mice, dogs, cats, chimps, you, me)

Body plans

Asymmetry

Radial symmetry – central axis

Bilateral symmetry – distinct left and right sides

dorsal (back side) ventral (belly side) anterior (head) posterior (tail)

TermsZygote – fertilized egg CleavageBlastula (hollow ball of

cells) pinches inward to form three GERM LAYERS:

EctodermMesodermEndoderm

Blastopore: opening into gastrula, it will become mouth in protosomes and the anus in deuterosomes