4.1- Features of the Animal Kingdom

Animals common ancestor

• similar to choanoflagellate protist

Features used to classify animals

• true tissues

• body plan: symmetry

• developmental pathway:

• 1. number of tissue layers

• 2. Origin of mouth and anus

• 3. Presence of a body cavity

Complex Tissue structure

• lack cell walls

• unique intracellular communication-gap junctions

• differentiation/ specialization of tissues

Specialization tissues

• connective tissues

• epithelial tissues

• nervous tissue

• muscle tissue

Asymetrial

• no symmetry (sponges)

Radial symmetry

• arranged around central axis with parts radiating outward

• can encounter environment from any direction

• jellyfish, comb jellies

Bilateral symmetry

• divides body along right and left halfs

• allows for cephalization, (anterior vs. posterior)

• suited for moving forward

Embryonic Development- 1. Cleavage

• series of mitotic cells with no cell growth

• after three divisions→

• cell continues to divides and or rearrange

Embryonic Development- 2. Blastulation

• forms blastula

• migration of cells

Embryonic development 3. gastrulation

• forms gastrula

• forms blastopore and archenteron

• sets up formation of outer and inner germ layers

• organogenesis gives rise to tissue, organs and organ systems

Diplolasts

• two germ layers: ectoderm and endoderm

• radial symmetry

• Cnidarians

• Ctenophores

Triploblasts

• three germ layers: ectoderm, mesoderm, endoderm

• bilateral symmetry

• all other animals

Coelom

• body cavity

• derived mesoderm germ layer

• lies between body wall and visceral organs

• fluid filled

• improved mobility

• organs can move within

• aceolomates

• pseudocoelomate 

• coelomates

Acoelomates- coelom

• mesoderm filled with tissue

• plathyhelminthes (flatworms)

Pseudocolelomates- coelom

• false body cavity

• derived from both

• still functional

• nematodes

Coelomates- coelom

• body cavity and internal organs lines with epithelial membrane

• tissue holds organs in place, allowing motion

• most other animals

Protostomes

• blastopore becomes the mouth, anus second opening

Deuterostomes

• blastopore becomes anus, mouth forms a second opening

Cleavage patterns- protostomes

• spiral cleavage

• determinate cleavage: fate of cells determined

Cleavage patterns- Deuterostomes

• radial cleavage

• indeterminate cleavage: fate of cells determined somewhat

Digestive system: incomplete

sac like cavity with one opening that serves as both mouth and anus (gastrovascular cavity)

Complete digestive system

• separate mouth and anus

Nervous System- Cephalization

• concentration of nerves and sense organs at anterior end of body, forming a head a brain

Body Patterns- segmentation

• organism is divided into a linear series of repeating, similar units along its anterior-posterior (head-to-tail) axis

Animal Reproduction

• most animals diploids

• reproduce sexually

Direct Development

• grows without larvae stage

Indirect Development

• larvae stage

Incomplete metamorphosis

• young resemble small adult

Complete metamorphosis

• organism looks different in each stage

Hox Genes

• master regulatory genes that control embryonic development (code for transcription factors)

• determines body plant, segmentation, number and placement of appendages, embryonic polarity

Cambrian period

• 542-488 MYA

• most of todays phyla originated'

• explosion of animal life

Post Cambrian 

• global and regional climate change

• lead to mass extinctions

• loss of diversity

Permian Triassic Boundary

• greatest extinction event due to climate change from impact events and/or volcanic activity

• extinction of 95% species