Invertebrates

A. Symmetry: radial -> bilateral

1. mouth and anus separate
2. hierarchical nervous system with frontal dominance, i.e. "brain"

B. Tissue types: diploplastic -> triploplastic - addition of a mesoderm between endoderm and ectoderm

C. Development of the body cavity

1. acoelomate - no cavity, solid mesoderm
2. pseudocoelomate - cavity with mesoderm on one side
3. coelomate - cavity within mesoderm - permits more complicated internal organ structure

II. Protostome - Deuterostome differences

A. oral development

1. protostome - blastopore becomes mouth
2. deuterostome - blastopore becomes anus

B. embryonic cell fate

1. protostome cells have determinate fates, i.e. cannot form complete organism
2. deuterostome cells have indeterminate fates, i.e. can form complete organisms

C. embryonic cell cleavage pattern

1. protostome exhibits spiral cleavage
2. deuterostome exhibits radial cleavage

D. origin of mesoderm

1. single cell near blastopore
2. pair of pouches from endodermal wall of archenteron

II. Protostomes without true coelom

A. Acoelomate: Phylum Platyhelminthes - flatworms

1. Class Turbellaria - free-living flatworms - Planaria
2. Class Trematoda - flukes

a. Schistosomes have 2 alternate hosts, mammals and snails
b. other flukes have 3 hosts

3. Class Cestoda - tapeworms

a. have 1 or 2 hosts
b. segmented, with each segment a complete reproductive unit

B. Pseudocoelomate: Aschelminthian Phyla

1. Phylum Rotifera
2. Phylum Nemata - Nematodes - extremely abundant, some parasitic

III Coelomate Protostomes

A. Phylum Lophophores - bryozoans and brachiopods
B. Phylum Mollusca

1. Class Gastropoda - snails and slugs
2. Class Bivalvia - clams, mussels, oysters, scallops
3. Class Cephalopods - squid and octopus

C. Phylum Annelida

1. Class Polychaeta - marine worms
2. Class Oligochaeta - earthworms
3. Class Hirudinoidea - leeches

D. Phylum Onychophora

1. velvet worms (Peripatus) do not have exoskeleton
2. have segmented body, with nephridia (water regulatory organ) in each segment
3. but have open circulation like an arthropod
4. and tracheae for gas exchange

E. Phylum Arthropoda

1. Innovations

1. reduction of segments into head, thorax and abdomen
2. jointed and specialized appendages
3. increased cephalization

2. Subphylum Trilobita - dominant in Paleozoic, now extinct

3. Subphylum Chelicerata

a. Class Arachnida - spiders, scorpions, whipscorpions, mites
b. Class Merostomata - horshoe crabs

4. Subphylum Crustacea

a. barnacles
c. crabs, shrimp, crayfish, lobsters
d. copepods, amphipods, isopods - "pillbugs"

5. Subphylum Uniramia

a. Class Chilopoda - centipedes
b. Class Diplopoda - millipedes
c. Class Insecta

IV Deuterostomes

A. Phylum Echinodermata

1. Key features

a. Radially symmetric (secondarily acquired)
b. Internal skeleton
c. No brain, radial nerve network

2. Class Stelleroidea - starfish and sea stars

3. Class Echinoidea - sea urchins, sand dollar

4. Class Holothuroidea - sea cucumbers

B. Phylum Hemichordata - acorn worms

C. Phylum Chordata

1. Subphylum Tunicata - sea squirts

a. have notochord in larval form
b. adults are sessile with pharyngeal pouch

2. Subphylum Cephalochordata - lancelets, Amphioxis

3. Subphylum Vertebrata- next lecture!