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