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|Blase Christopher Billack
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|TOPIC OF THE MONTH (8/15/99-9/15/99): SEA URCHIN DEVELOPMENT|
|The sea urchin is an animal that belongs to the Echinodermata family. It is related to other marine species such as the starfish and the sea cucumber. The sea urchin has been used for at least 100 years in the study of embryo development. The eggs of the sea urchin are readily obtainable in large numbers AND can be easily visualized with the light microscope. (Sea urchin spermatozoa are also easily obtained in large numbers and though much much smaller than the egg, can also be seen with the light microscope). The fact that these reproductive cells can be easily isolated and visualized has predisposed the sea urchin to be a model for the study of animal embryo development. The above figure depicts the series of developmental changes that occur in the egg following fertilization. Within 1-2 minutes after fertilization, the egg expands a membrane called the fertilization membrane, the purpose of which is to prevent polyspermy (fertilization by more than one sperm cell). Within 1 hour of fertilization, the egg divides into 2 cells (two cell stage). By the second hour after fertilization, the two cells have divided into four cells (four cell stage) .... and so on and so forth. The embryo develops into pluteus stage approximately 36 to 48 hours following fertilization. The pluteus can be considered a "baby" urchin. It is able to swim (powered by cilia) and eat plankton. Sea urchin development beyond the pluteus stage is often difficult to observe in the laboratory setting.
Giudice, G. (1986). The Sea Urchin Embryo: A Developmental Biological System.
New York: Springer-Verlag.
Stearns, L.W. (1974). Sea Urchin Development. Dowden, Hutchinson & Ross, Inc.
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|PICTURE OF ADULT SEA URCHIN