An Introduction to Animal Diversity

Chapter 32

Characteristics of Animals

• 1. Multicellular eukaryotes• 2. Heterotrophs • 3. No cell walls • 4. Specialization • 5. Locomotion• 6. Sense organs • 7. Sexual reproduction

Animals are multicellular eukaryotes that primarily reproduce sexually.

After fertilization the zygote undergoes cleavage - rapid cell division

Animals are multicellular eukaryotes that primarily reproduce sexually.

Leading to the formation of a blastula

Animals are multicellular eukaryotes that primarily reproduce sexually.

Forming the different layers of embryonic tissues through gastrulation.

Hox genes• Regulatory genes• Regulate

development of embryo

• Similar among many animal species

• Homeoboxes– Common set of DNA

sequences– Hox genes are one

type of homeobox

Cambrian explosion (535 to 525 MYA) earliest fossil appearance of many major groups of living animals.

Cambrian explosion (535 to 525 MYA) earliest fossil appearance of many major groups of living animals.

Diversity increases through Paleozoic but punctuated by mass extinctions

Cambrian explosion (535 to 525 MYA) earliest fossil appearance of many major groups of living animals.

Animals begin to make impact on land – 460 MYAVertebrates transition to land – 360 MYA

During Mesozoic (251-65.5 MYA) coral reefs emerge and dinosaurs dominant.

65.5 MYA the start of the Cenozoic era followed mass extinction and modern mammal orders diversify.

Body Plans of Animals• Body plan

– Set of morphological and developmental traits

• Asymmetrical – absence of symmetry

• Radial – top and bottom, no front or

back, no left or right• Bilateral

– Two axes of orientation: front – back, top - bottom

Dorsal - topVentral - bottomAnterior – front (head)Posterior – backMedial - middleLateral – toward outside

Tissues• No true tissue – Parazoa

(Sponges)• True Tissues – Eumetazoa

– Groups of cells with a specialized function

– Germ layers• Diploblastic

– 2 germ layers• Triploblastic

– 3 germ layers• Ectoderm• Endoderm• Mesoderm

Body Plans of Triploblastic Animals• Coelom

– Fluid or air filled cavity

– Separates digestive tract from outer body wall

– Coelomates• Pseudocoelomates

– Functioning body cavity supported by presssure

• Acoelomates– No body cavities

Protostomes vs. Deuterostomes• Protostomes

– Spiral cleavage –– Determinate

• Determines fate of cells early on

– Blastopore becomes mouth

• Deuterostomes– Radial cleavage – Indeterminate

• Fate of cell not determine; leads to stem cells

– Blastopore becomes anus

Major Features of Animal Phylogeny – about 3 dozen phyla exist

Based on Morphology Data Based on Molecular Data