21. After fertilisation, each embryo develops within a day or so into a free-swimming planula larva. 22. The released eggs are fertilized, and the resulting zygote develops quickly into a multicellular " planula ". 23. After 3 days the egg develops in a planula ; at this stage movement is only done by ciliary action. 24. The free-swimming planula larvae eventually settle on the seabed and develop into juvenile polyps which found new colonies. 25. The fertilised egg develops into a planula , which settles after fifteen to twenty days and grows into a new individual. 26. The fertilized egg develops into a planula larva which drifts with the plankton before settling and developing directly into another polyp. 27. The egg hatches into a free-swimming planula larva that settles on the seabed when it has completed its development. 28. Reproduction involves the release of planula larvae which spend somewhere between a few hours and several days in the open sea. 29. Planula larvae that develop from fertilised eggs sink to the seabed five days later and undergo metamorphosis to found new colonies.30. As a planula settles down, it gives rise to a colony of polyps that are attached to the sea-floor.
