- Believed to be amongst earliest multicellular animals on eart. Oldests fossil = 600 million years old.
- found in seas all over the world, few species live in fresh water.
- Sponges are animals as they have cells with no cell walls.
- Some have flagella, beating rhythmically, creating a water current that flows through sponge's body where they can extract food material.
- Flagella cells also have microvilli - increase surface area, therefore making food absorption more efficient.
- Other cells are tubula, providing pores where the water current can circulate. Others secrete collagen, others secrete little spicules of calcium carbonate (silica) which provide a skeleton for the sponge.
- Like most multicellular organisms, have specialised cells.
- However, they don't posses true tissues…