L5 The origins of the metazoans Flashcards
What is the hypothesised origin of the metazoans?
Colonial theory - From a colonial flagellate, Thought that differentiation among the colony gave rise to the earliest animal, and each having different roles many they had to stay together to function
What is a colonial flagellate?
A unicellular organism characterised by by the presence of flagella
What is the evidence for colonial theory?
Flagellated cells found in metazoans
Flagellates often form colonies
Molecular evidence in similarities of differential gene expression
What are choanoflagellates?
Are essentially collard cells held in a matrix, funnel shaped collars,
What is the phylum Porifera?
The sponges
Which branch of the metazoans are sponges on?
Parazoa, meaning ‘besides the animals’
What symmetry do sponges display?
No symmetry, meaning they can grow in many forms
How long have they been around?
Suggested are the oldest animals, have been highly successful and widespread for millions of years
Describe the cellular organisation in sponges
No organs or tissues, cells restock together in a matrix, with groups performing different functions
Where do sponges live?
Mostly marine, some freshwater
What is the mode of life of sponges?
Are sessile, but some have relationships with other animals, like crabs, so can move around
What forms do sponges take in high currents?
Flatter
What forms do sponges take in low food source areas?
Less current in deep waters means there is less food, so sponges grow big and branched
What is a choanocyte?
Collar cells which generate a water current in the sponge by wafting their flagella
What is the osculum?
There the water is expelled, through the top of the sponge
