25.1 Animal Origins

What is an animal?• Multicelled,

heterotroph

• Most motile

• Reproduce sexually

• Unwalled

• Most have tissue and organs

Evolutionary Tree

Tissues

Key innovation in complexity:• Ability to interact in

functional units Epithelium

• Sheet like array

• Functions: absorption, secretion, sensory

• 1st epidermis

• 2nd gastrodermis

cont.

Connective tissue• All contain

• Most have a matrix in which living cells and protein fibers (collagen) exist

Embryo forming – 2 primary tissue layers• Outer ectoderm

• Inner endoderm

• mesoderm

Body Size

How to deal with increasing constraints of SA-V ratios of cells?• Pseudopds and microvilli in single cell species

• Simple animals are sheets/ribbons

• circulatory system in large animals

Where did it all start?

Colonial Theory • 1st animals evolved

from tiny colony of flagellated, amoeba like cells

• Choanoflagellates Share common

ancestor with sponges

25.2 Basic Body Plans

Body Symmetry• Polarity – front to

back axis, with anterior and posterior ends

• Radial – organized around main axis, water

• Bilateral – right and left halves along a main axis Cephalization –

distinct head region

Gut and Body Cavity

Incomplete gut• Sac-like

• One opening

• 1st to evolve

Complete gut• Tubular

• 2 openings

• Mouth (specialized feeding structures) to anus

Formation of Complete Gut

Protostomes• 1st opening

becomes mouth

• Flatworms, mollusks, annelids, roundworms, arthropods

Deuterostomes• 1st opening

becomes anus

• Echinoderms, chordates

epidermis gutcavity

organs packed betweengut and body wall

No coelom(acoelomateanimals)

Fig. 25-6a, p.406

None – flatworms, few invertebrates• Tissue and organs fill

region between gut and body wall

epidermis

gutcavity

unlined body cavity around gut

Pseudocoel(pseudocoelomateanimals)

Fig. 25-6b, p.406

Pseudocoel – roundworms• In some protostomes coelom is reduced/lost

epidermis

gutcavity

peritoneumbody cavity with lining thatholds internal organs in place

Coelom(coelomateanimals)

Fig. 25-6c, p.406

Repeating Units

Favors regional specialization in structure and function

Segmentation – annelids, arthropods, vertebrates• Divide into a series of functionally connected units

along main body axis

Phylum Examples Evolutionary Milestone

Porifera sponges multicellularity

Cnidaria jellyfish, hydra, coral tissues

Platyhelminthes flatworms bilateral symmetry

Nematoda roundworms pseudocoelom

Mollusca clams, squids, snails coelom

Annalida earthworms, leeches segmentation

Arthropoda insects, spiders, crustaceans jointed appendages

Echinodermata starfish deuterostomes

Chordata vertebrates notochord