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 “Pseudocoelomates” Examples: 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”. Blastopore: the first opening into embryo, it will become mouth in protosomes and the anus in deuterosomes. Protostome- Coelom originates from a cell mass. Deuterostome- Coelom originates from a digestive tube. The next several Phyla are all protostomes…..

First Protostome: Phylum: Mollusca A 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: Echinodermata Sea 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)

Terms Zygote – fertilized egg Cleavage Blastula (hollow ball of cells) pinches inward to form three GERM LAYERS: Ectoderm Mesoderm Endoderm Blastopore: opening into gastrula, it will become mouth in protosomes and the anus in deuterosomes