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
What is a porocyte?
Pores
What is the mesophyll?
Gel like matrix
What are pinacocytes?
A covering over the outside
What are incurrent pores?
Holes into the sponge, that water is drawn through
What are spicules?
Calcareous/silicious sponge fibres, like the skeleton of the animal, keeping the pores open.
What is the spongeocoel?
Cavity where water is drawn up
What are amebocytes?
Where digestion takes place. They secret spicules, and are totipotent
What drives the flow of water through the sponge?
Beating flagella, ensures water flow in one direction
What are the venus flower baskets?
Sponge made of silicates, 75% synticial tissues, which means have no cell boundaries, meaning electrical impulses can travel through the structure
How do sponges feed?
Most are filter feeders, taking organic material out of the water. Food is engulfed by the amebocytes. In some deep sea species, sponges have become carnivorous e.g. the harp sponge
Why are sponges crucial to life on coral reefs?
The in carbon and deposit it back in the environment in a form which other organisms can utilise
How do sponges reproduce?
Asexually by budding or gemmules, or sexually, when sperm is expelled though the osculum and engulfed by the choanocytes of other sponges. Eggs form, and larvae are retained until the blastula stage - usually hermaphrodites
What are gemmules?
In freshwater sponges, a cluster of cells is released, surrounded by spicules and filled with amebocytes, which emerge and form a new sponge when conditions are right
What did Wilson discover about sponges in the 1800s?
Sponges can regenerate, if put through a sieve, will reform. When two different sponges served and mixed, could reform into their original sponges, shows some level of immunoregulation
Why do some sponges produce biotoxins?
To get rid of competitors - creates a dead zone around the sponge, or to avoid predators
