Reflections: Sea Urchins

Today in lab we studied the development of sea urchins. In order to understand how sea urchins are developed, we need to understand the stages of animal development. The first stage in development is fertilization. Fertilization is the process in which the sperm and egg fuse together. The next stage is cleavage. This is where the cell will begin to have rapid miotic divisions which will form into a sphere called the bastula. Gastrulation is the next stage of animal development. This is the stage where the three germ layers, ectoderm, mesoderm and endoderm are formed. Each layer is specific to which part of the body will arise. The ectoderm will give rise to the epidermis, the mesoderm will give rise to the muscles and the endoderm will give rise to the dermis. The second to last stage of development is organogensis. This is the process in which organs are formed. The last stage is gametogenesis. Gametogenesis is the formation of gametes.

Within the lab today, we observed the first stage of animal development, fertilization. We first started off the process of fertilization by taking the sea urchins out of the tank and placing them into a basin of sea water for about a minute. Next we placed the  sea urchins upside down within the petri dish and took 2 mL of potassium chloride (KCl) and injected it into the bottom of the sea urchin. We then poured the sea water into a container and turne dthe sea urchins over to observe whether it was a male or a female sea urchin. The male sea urchins gametes were white and the female sea urchin's gametes were yellow. After this was done, we looked at the egg under the microscope and the sperm under the microscope. Next we took the slide with the egg and placed a drop of sperm onto the slide and watched the fertilization process begin. At first the egg sat there for a few seconds then out of no where, the many many sperm came out of no where and quickly rushed to the egg. Within a matter of seconds the fertilization envelope was formed such that there will be a block of any more sperm from fertilizing the egg and creating polyspermy. Here is a picture of the sperm trying to enter through the fertilization envelope that has formed.

I really enjoyed this lab. It was the first time I was able to see fertilization done within that amount of time. Although I was not able to observe the rest of the stages, one day I hope to see the cleavage stage within the gametes of the sea urchins. I think it would be amazing if I was able to see the cell divide into many cells and begin to differentiate. Overall I really enjoyed this lab, I just wish we were able to view the sea urchins through the clevagage and gastrulation stage.