At first sight, this echinoderm doesn't have an attractive appearance and it seems not to have interesting microscopic features. I hope that this article, which doesn't want to be an exhaustive lesson on its family, will permit me to introduce some amazing and lesser known aspects on its anatomy and mainly to illustrate them. Sea urchins appeared on earth around 500 millions years ago . Nowadays they are often used as models for exploration of the development process in living organisms. A classical biology course will cover in vitro fertilisation of urchin eggs and their observation.
Eggs are orange-coloured and sperm is white.
Eggs can be diluted immediately with sea water, but sperm must be aspirated from the pore and stored like this. The two samples can be cooled separately and used until two or three days later for fertilisation by mixing eggs and sperm very diluted in sea water. Like many marine animals, sea urchins produce a great number of eggs, which are carried away by currents and only few of them become adults. When an egg is fertilised by sperm, its envelope increases in size, divides itself in two, then four, then eight cells and so on. This process occurs freely in sea water.