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Why do sea urchins have external fertilization?
Fertilization is external. To prevent the sperm and eggs from being washed away and diluted, sea urchins have evolved mechanisms to bring the gametes together, including synchronizing spawning and chemotaxis of the sperm towards the egg (Gilbert, 6th edition, Figure 7.9).
How many eggs are produced by sea urchins?
Fertilization. Sea urchins typically spawn near the surface. Males release sperm into floating plankton, then female urchins release between eight and 20 million eggs in the same area.
Why do sea urchins reproduce sexually?
Although Purple Sea Urchins are dioecious, meaning they have separate male and female sexes, it is hard to distinguish the two because they are very similar. Instead, they spawn, meaning that they release their eggs and sperm into the water, reproducing sexually. …
How is fertilization achieved in sea urchins?
Comparative Reproduction Male and female sea urchins are easily induced to shed massive numbers of eggs or sperm. The eggs are mature at release and are fertilized externally simply by mixing egg and sperm. The resulting embryos are optically transparent and develop synchronously in nothing more than sea water.
How are sea urchins able to reproduce on their own?
Instead, they spawn, meaning that they release their eggs and sperm into the water, reproducing sexually. In particular, Sea Urchins leave reproduction to chance. They do not select a mate, but rather release their gametes and leave it to chance that they will mix and get fertilized. Only 10% to 40% of eggs get fertilized.
What to do with the eggs of a sea urchin?
The eggs will then be shed into the sea water and settle down to the bottom of the beaker. Store the eggs at the same temperature as would be best for development in this urchin. Use a fairly high concentration of sperm to maximise viewing of living sperm under a microscope, 40x objective is best.
When does a purple sea urchin reach sexual maturity?
Purple Sea Urchins reach sexual maturity after about two to three years. They do not show courtship or special behavior towards their mate. Instead, they spawn, meaning that they release their eggs and sperm into the water, reproducing sexually. In particular, Sea Urchins leave reproduction to chance.
How many chromosomes do sea urchins have?
A Sea Urchin haploid cell contains 21 or 22 chromosomes, which contain the genetic information that is passed on to offspring. They use external fertilization in reproduction. The male releases sperm and the female releases eggs.