Leftover Sea Urchins

  1. Probably the best solution is to return them to their homes, the sea. (Remember to return to them to the same place they were collected so their chances of survival are the greatest.)
  2. Pets. If you purchased your urchins and you do not live near the ocean, but you do have a saltwater aquarium going in your class, you could keep them around for the rest of the year. Some species will even produce more gametes in "captivity". We routinely recycle L. pictus for our work this way.
  3. Taxidermy. There is a limit to how many you might want to use for this process.
    1. With a pair of forceps remove the mouth and all internal organs. (dispose of organs)
    2. Place the shell with spines intact into 95% alcohol for 24 hours. (pure denatured alcohol)
    3. Remove from alcohol and allow to air dry.
    4. The urchin will be relatively smell free at this point and can be used for discussions, displays, props for science fair projects, etc. Should keep for years and years.

Leftover Embryos

Life being what it is, it is not always possible that the urchins will spawn every time, every year. By preparing ahead for the "lean" years, you can still put on a pretty good lesson.

Fixing Gametes And Embryos

Warning: all operations should be done in a fume hood. Gloves and safety glasses should be worn.
It must ony be done by the teacher; it's toxic and cancerous!
  1. Take a commercial solution of formaldehyde, 37% and mix one part with 9 parts seawater.
  2. Let the embryos settle or spin them down gently in a low speed centrifuge. Pour off the seawater and add the Fixing Solution. Place in a refrigerator for at least 24 hours.
  3. The fixed embryos will no longer be osmotically sensitive. Gently pour off the fixative (hazardous waste) and without letting them dry add distilled or deionized water.
  4. Do one more rinse in distilled or deionized water (10 minutes in each rinse).
  5. At 10 minutes each, gradually go through a graded alcohol series. 30%, 40, 50, 60, 70.
  6. Embryos may be stored for some time in 70% alcohol (months, if not years?). They can be used in this state or proceed to making permanent slides.

Safer Alternative: (OK, not as good as above, but definitely safer.)

  1. Rinse embryos in 10% glycerol (90% distilled or deionized water) three times, either using gentle centrifugation or settling to get eggs to bottom.
  2. Place concentrated embryos into 70% ethanol. There will be some distortion, but not too bad.

Making Slides, Temporary:

To either of above methods, let embryos settle (usual case if they have been sitting in a refrigerator for a year). Then add a few drops of concentrated embryos to a 10% glycerol solution. Mix gently. They are now safe for students to handle and observe under a microscope.

Permanent Slides:

Method 1 (safer): add concentrated embryos to 100% glycerol. Add drop to microscope slide and a cover glass. Seal edges of cover glass with finger nail polish. This will be hard to do if there is glycerol coming out from under the cover glass.

Method 2 (dangerous solvents used): continue alcohol series with 80%, 90%, 95%, 100%, 100%. Then add 50% pure alcohol with 50% toluene or xylene. Next 100% toluene or xylene. Finally place a drop on a slide and cover with a few drops of Canada balsam dissolved in toluene or xylene. Add a cover glass. The slide will harden in a few days and be very permanent. Once the slide is dry it is non-toxic.

Also see Carnoy's Fixative in the Extended Research Ideas section.