Invertebrate Zoology Sea Urchin Embryology Lab


Species:  Eucidaris tribuloides



  1. Add 10 ml of filtered seawater to one the “gamete shedding” cups.


  1. Invert an urchin over the cup so its mouth (oral side) is up.  (The five gonopores are on the aboral surface, so in this position the gametes will be shed into the cup.


  1. To induce the release of the gametes, use about 0.5 to 1.5 ml of 0.5 M solution of potassium chloride (the amount to use depends on the size of the sea urchin).


  1. Carefully insert the hypodermic needle through the soft tissue surrounding the mouth and inject the solution into the central cavity.  Gametes should begin to be released within 2 to 5 minutes following the injection.


  1. The eggs appear yellowish while the sperm are white and milky.  The eggs should be washed several time with filtered seawater by allowing them to settle to the bottom of the cup, decanting the old water, and adding fresh seawater.  (The eggs can be held at room temperature for several hours before use, while the sperm are viable in dilute condition for a shorter time.)


Observing fertilization and development of fertilization membranes

 To prevent fertilization from occurring in the cup, make sure you use a different pipette for each suspension.


1.      To observe fertilization and development of the fertilization membrane, place a drop containing eggs on a slide and cover with a cover slip (you can also try a depression slide). 


2.      Add a drop of sperm suspension to the edge of the cover glass so it comes in contact with the water in the egg suspension.  The sperm will diffuse under the cover slip and the events of early fertilization can be observed.  The sperm should be added to the slide after it is positioned on the microscope stage, as fertilization can occur within 30 seconds of sperm contact.


The first division should begin about 80 minutes after adding the sperm suspension.  Development of the eggs will continue through a series of divisions.  The blastula stage can usually be observed in 18 to 24 hours, early gastrula in 30 to 36 hours, and early pluteus (larvae) in 72 to 80 hours.  Development time can vary slightly because of difference in conditions in the laboratory.