ACOELOMATE ANIMALS
PHYLUM PORIFERA
Poorly-defined tissue layers
Lack basal lamina
Silica spicules
Choanocyte collar cells
Protospongia hicksi 520 MYA (Early/Middle Cambrian)
Proterospongia?
Colonial choanoflagellate
Colonial organisms?
Local example: Spongilla lactustris
Cosmopolitan or encrusting
Chlorella symbiont
Gemmules
Chitinous & filled with archaeocytes!
The common ancestor was probably a colonial flagellated protist;
Similar to existing colonial choanoflagellates and sponges.
Cells in the colony began to specialize for different functions.
Distinct layers of cells form in early (embryonic) development:
Diploblastic animals have 2 cell layersectoderm and endoderm.
Triploblastic have 3 cell layersecto-, endo-, and mesoderm
Evolution of a body cavity:
Acoelomate
Pseudocoelomate
Coelomate
PHYLUM CNIDARIA
Diploblasts two true dermal layers!
Separates body compartments of different chemical compositions
Independent internal regulation
Cnidae
Nematocysts
Chemical & mechanical stimuli
Cnidocil trigger
HYDRA
Freshwater, individuals
Polyp = mature morphology
Reduction in water temperature slows growth, but increases size
H. viridis high carotenoids due to prey
PHYLUM PLATYHELMINTHES
Flatworms!
One-way digestive tract
Bilaterally symmetric
Mating
PLANARIANS
Dugesia tigrina
Eyespots & vision
Regenerative biology
ROTIFERA / GASTROTRICHA
Acoelomate animalsSlide Number 2Phylum poriferaSlide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Phylum cnidariaSlide Number 12HydraSlide Number 14Slide Number 15Phylum platyhelminthesPlanariansRotifera / gastrotricha