Introduction To Animal Evolution

Chapter 32

• Animals 1st appeared in Precambrian in waters, spread to land.

• 5 criteria that define animal:• 1Animals multicellular, must get

food through ingesting other organisms or organic material.

http://www.biology.wustl.edu/plant/simplealgalsystems1.jpg

• 2Animals do not have cell walls.• 3Animals have nervous tissue to

conduct impulses and muscle tissue for movement.

• 4Most animals reproduce sexually with diploid stage being dominant.

• 5Animals have special regulatory genes (Hox genes) help zygote form into animal.

Branching of evolutionary tree

• 1st branch point splits Parazoa (lack true tissues) from Eumetazoa (true tissues).

• Parazoa include sponges.• Eumetazoans divided into 2

major branches, partly based on body symmetry.

http://www.sciencedaily.com/images/2007/07/070705153000.jpg

• Radial symmetry - phylum Cnidaria and phylum Ctenophora.

• Bilateral symmetry (left and right side) - rest of phyla.

• Bilateral symmetry - cephalization, - concentration of sensory equipment towards head.

• Difference between 2 groups - presence of germ layers - layers of embryonic tissue that form various tissues and organs.

http://www.guam.net/pub/sshs/depart/science/mancuso/apbiolecture/27_Animalia/Annelida/Image11.gif

• Bilaterally symmetric animals - 3 germ endoderm (innermost), mesoderm (middle) ectoderm (outermost).

• Bilateral animals split according to presence of body cavity (fluid-filled space separating digestive tract from outer body wall) and what cavity looks like.

http://universe-review.ca/I10-13-layers.jpg

• Acoelomates (phylum Platyhelminthes) have solid body, lack body cavity.

• Some organisms - body cavity - not completely lined by mesoderm.

• Pseudocoelomates include rotifers (phylum Rotifera), roundworms (phylum Nematoda).

• Coelomates organisms with true coelom, (fluid-filled body cavity completely lined by mesoderm).

• Body cavity has many purposes including cushioning organs, allowing them more room to grow.

• Coelomate phyla divided based on differences in development.

• Many protostomes (mollusks, annelids, arthropods) undergo spiral cleavage.

• In many protosomes, blastopore develops into mouth; 2nd opening at opposite end of gastrula develops into anus.

http://chsweb.lr.k12.nj.us/mstanley/outlines/animals/antax/image51.gif

• Zygotes of many deuterostomes undergo radial cleavage.

• Deuterostomes - blastopore usually develops into anus, mouth derived from 2nd opening.