1. Animals!
Introduction

2. What is an animal? Structure, nutrition and life history
define animals…
While there are exceptions to nearly every criterion for distinguishing an animal from other life forms, five criteria, when taken together, create a reasonable definition.
Multicellular, heterotrophic eukaryotes
No cell wall
Nervous and muscle tissue
Sexual reproduction, diploid dominant
Unique regulatory gene for development

3. 1. Multicellular, heterotrophic eukaryotes
They must take in preformed organic molecules through ingestion, eating other organisms or organic material that is decomposing.
They gotta eat!

4. 2. No cell wall
Animal cells lack the cell walls that provide strong support in the bodies of plants and fungi.
The multicellular bodies of animals are held together with the extracellular proteins, especially collagen.

5. 3. Nerves and Muscles Animals have two unique types of tissues:
nervous tissue for impulse conduction
muscle tissue for movement

6. 4. Sexual reproduction, diploid stage dominates life cycle
small flagellated sperm fertilizes a nonmotile egg
zygote undergoes cleavage, a succession mitotic cell divisions, leading to the formation of a multicellular, hollow ball of cells called the blastula.
During gastrulation, part of the embryo folds inward, forming the blind pouch characteristic of the gastrula
This produces two tissue layers: the endoderm as the inner layer and the ectoderm as the outer layer.

7. 5. Regulatory genes: Hox genes
Hox genes: Regulatory genes that act in the developing embryo to control the transformation of a zygote to an animal of specific form
regulate the expression of other genes
contain common DNA sequences,
called homeoboxes
All animals, from sponges to the most
complex insects and vertebrates have
Hox genes
the number of Hox genes correlated
with complexity of the animal’s anatomy.
variation in when and where the Hox genes are expressed in a developing embryo provides the genetic basis for the great diversity of animal forms that have evolved from a common ancestor

8. Animal evolution
The animal kingdom probably evolved from a colonial, flagellated protist
Ancestor lived over 700 million years ago in the Precambrian era.
probably related to choanoflagellates
Modern choanoflagellates are tiny, stalked organisms inhabiting shallow ponds, lakes, and marine environments

9. Phylogenetic Tree of Animals
Phylogeny is changing due discoveries in molecular biology
The traditional view of relationships among animal phyla are based mainly on key characteristics of body plans and embryonic development.
There are four main branches…

10. 1. Parazoa vs. Eumetazoa Parazoa: lack true tissues
Phylum Pofifera: sponges – unique development and structural simplicity
Eumetazoa: have true tissues
Tissues are a basic feature of all other animal phyla

11. Radiata: Radial Symmetry
2. Radial vs. Bilateral Symmetry Eumetazoans divided based on body symmetry
Radiata: Radial Symmetry
phylum Cnidaria (hydras, jellies, sea anemones and their relatives) and phylum Ctenophora (comb jellies)
Diploblastic: two germ layers - ectoderm, covers surface of the embryo, endoderm, the innermost layer, lines the developing digestive tube

12. Bilateria: Bilateral Symmetry
Have a dorsal and ventral side, an anterior and posterior end, and a left and right side.
Cephalization: concentration of sensory equipment on the anterior end (a brain!)
Triploblastic: third germ layer, mesoderm lies between the endoderm and ectoderm
develops into the muscles and organs

13. 3. Body Cavity Acoelomates: triploblastic animals with solid bodies
Do not have a cavity between the digestive tract and outer body wall
phylum Platyhelminthes

14. Pseudocoelom: there is a body cavity, but it is not completely lined with tissue derived from the mesoderm.
include the rotifers (phylum Rotifera) and the roundworms (phylum Nematoda)

15. Coelomates: organisms with a true coelom, a fluid-filled body cavity completely lined by tissue derived from the mesoderm.
The inner and outer layers of tissue that surround the cavity connect dorsally and ventrally to form mesenteries, which suspend the internal organs.
Functions:
cushions the suspended organs
hydrostatic skeleton in some animals
enables the internal organs to grow and move independently to the outer body wall

16. 4. Protostomes vs. Deuterostomes Coelomate phyla are divided based on differences in their development.
Protostomes
spiral cleavage: planes of cell division are diagonal to the vertical axis of the embryo
Coelom formation begins in the gastrula
Blastopore forms the mouth
The mollusks, annelids, arthropods

17. Deuterostomes
radial cleavage: the cleavage planes are parallel or perpendicular to the vertical egg axis
Coelom forms from the mesodermal outpocketings
Blastopore forms the anus
echinoderms, chordates (you!)