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 dominate. 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 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.