Fertilization and Embryology of Sand Dollars

ROBERT W. WRIGHT, Garfield High School, Seattle, Washington 98122 Downloaded from http://online.ucpress.edu/abt/article-pdf/31/3/184/25077/4442465.pdf by guest on 23 September 2021

O bserving the actual process of fertilization is for 500 students' use. When collecting the sand a highly motivating student activity. The phylum dollars, rinse them free of sand and place them Echinodermata provides many species which serve oral side down in a two-gallon plastic bucket, or as ready sources of easily used gametes. Biology other large, non-metal container, filled with clean teachers having access to marine habitats should be sea water. Additional clean sea water should be aware of the ease of collection, maintenance and collected for culture of the sand dollars upon return use of Echinoderms since these organisms may be to the classroom. transported and kept alive far from their normal environments. Maintenance of Sand Dollars Although sea urchins (Strongylocentrotus pur- Immediately on return to the classroom remove puratus, and S. drobachiensis) have received the the sand dollars from the collecting bucket and place distinction of being reliable gamete sources, other them singly into culture dishes. Add about 200 cc of species of Echinoderms might be used with equal unfiltered sea water to each dish and refrigerate at success. The sand dollar, Dendraster excentricus, approximately 6?C. We have found that the orga- has provided the author with a very dependable nisms will remain alive in this condition for at least source of material for fertilization experiments. 40 days without feeding or water change. We have also found that sand dollars will remain alive for four Collection of Sand Dollars days at 24?C and, if cooled to 12?C, remain alive Dendraster excentricus usually inhabits the low thirty days. This additional information may be use- tide horizon of sand beaches. They lie just under ful for persons intending to transport the sand dollars the sand and can be so numerous that the collector long distances. feels at ease to take more than are actually re- D. excentricus also has been stored in plastic dish quired. pans in our classrooms. Place about ten animals to In the Puget Sound region of Washington, the each pan with enough sea water added to cover the sand dollars are collected for use about the third topmost animal. Place the pan or other container week of April. It has been our experience that in the refrigerator at about 6?C. When kept in this D. excentricus is sexually mature from March manner, daily checking is required, and the length through September, although the largest proportion of time the animals can be maintained is shortened of sand dollars collected shed gametes about April to ten days. 20th. Avoid placing the sea water or the sand dollars Collect four or five animals for each class if in- in metallic containers as excess metallic ions have ducing the organism to shed gametes is to be done deleterious effects on marine invertebrate animals. as a class-room demonstration. If only the gametes are to be used for fertilization demonstration and Obtaining the Gametes experimentation, 10 sand dollars will provide gametes Gametes of the sand dollars are collected by

184 THE AMERICANBIOLOGY TEACHER, MARCH, 1969 injecting the animals with aqueous 0.5M potassium by the development of a fertilization membrane. chloride solution (Tyler, 1949). Using a syringe In many cases, the fertilization membrane will equipped with a 25 or 27 gauge, ?3 inch needle, be fully formed 6 minutes after mixing the gametes inserted through the organism's mouth, inject about and the first cleavage division of the egg will 0.5 cc of the potassium chloride solution. Hold the occur within 40 minutes if the eggs are kept at syringe so that the needle is as nearly parallel to the room temperature. The developing embryos can animal's oral surface as possible. After injection, be maintained in clean sea water at 15?C for 72 hours place the sand dollar in a culture dish with enough at which time many echinopluteus larva will be clean sea water to cover it. Gamete shedding will seen swimming throughout the container. Those occur in 2-3 minutes. The gametes are shed from investigations considering the effects of temperature five gonopores located at the base of the familiar or salinity on the developing sand dollar embryos star design on the animal's aboral surface. As the are among the most easily attempted student ex- sand dollar shows no sexual dimorphism, the ex- periments. perimenter is forced to wait for the gametes to as- certain the sex of the animal. The gametes, once released, can be pipetted into *REFERENCES

culture dishes containing cool (150 to 20?C) sea BEVELANDER, GERRIT, and NAKAHARA, HIRoSHI, 1962. The de- Downloaded from http://online.ucpress.edu/abt/article-pdf/31/3/184/25077/4442465.pdf by guest on 23 September 2021 water. These gametes can be stored at 6?C for up to velopment of the embryo of the sand-dollar Echinara- 36 hours before using. Take care to avoid mixing the chnius parma. Turtox News. 40:131-132. COSTELLO, D. P. et al., 1957, Methods for obtaining and han- eggs and sperms before you are organized to watch dling marine eggs and embryos, Marine Biological Labora- the fertilization process. tory, Woods Hole, Massachusetts, 247 p. Students usually study the process of fertilization GRAVE, C., 1902, A method for rearing marine larvae. Sci- by observing separate drops of egg and sperm sus- ence. 15:579-580. TYLER, A., 1949, A simple, non-injurious method for inducing pensions, then combining the drops to note the fer- repeated spawning of sea urchins and sand dollars. Col- tilization process. Upon mixing, fertilization is noted lecting Net. 19:19-20.

ment, newsreel film clips and interviews with his two D~~ ~~~~~------Wl , '1:! sons and Lord Richard Calder, friend and colleague of Wells. The accuracy of the predictions made in his many novels is reviewed along with testimony to / Editedby George Vuke Wells' frustration at being recognized as an author Audio-Visual Center,Indiana University but not as a scientist. This is one of eight films in The Creative Person series. Films The Beginnings, 16 mm, 24 min., color, 1968, Graphic Five super or standard 8mm films on flagellates, Curriculum Inc., Box 565, Lennox Hill Station, ciliates, and amebas are available at $18.50 per car- New York, New York 10021. tridge from Thorne Films, 1229 University Avenue, This is one of nine films in the Animal Secrets Boulder, Colorado 80302. Flagellates, Part I shows series shown on NBC television in 1968. After spec- movements of Euglena, Chilomonas, and Peranema; tacular scenes of volcanic eruptions, the film settles Flagellates, Part II, interesting scenes of the removal down to the less visually spectacular but nonetheless and puncture of the gut of a termite and examination interesting comments of Dr. Loren Eiseley on the of Triconympha; Citiates Part I, Paramecium, Spiros- origin of life, scenes of DNA models and new dis- tomum and Stentor; Ciliates Part II, Vorticella, Hal- coveries in the laboratories of Dr. Cyril Ponnam- teria and Stylonchia. The Ameba cartridge includes peruma, Dr. Sidney Fox, and others. The film will Ameba, Vehikampfia and Arcella. In general, the probably maintain interest for most viewers even contrast, sharpness and magnification of the speci- through the few visually weak sequences because the mens are adequate for showing gross movements and main topic of the film, "How Did Life Begin?" is the shapes but mediocre for internal structures. The films center of much research and excitement. Dr. Eiseley begin with a brief scene of a simple slide preparation concludes with the familiar quotation from Tenny- or collection and end with crudely drawn sketches son's "Flower in a Crannied Wall." of the specimens shown by photomicrography. The films are 3-4 minutes long and 1967 releases. H. G. Wells, Mall of Science, 30 min. B/W rental $5.40, National Educational Television, Audio- N otes Visual Center, Indiana University, Bloomington, A series of photomicrographs of specimens com- Indiana 47401. monly studied in introductory biology is available This film presents the biography of H. G. Wells with from Educational Methods Inc., 20 Huron Street, Chi- an emphasis on his scientific training. The highlights cago, Illinois 60611. These photographs, with lines in- of his life are portrayed with still photographs, enact- dicating structures, are on 81/2 x 11 sheets and cost

FERTILIZATIONAND EMBRYOLOGYOF SAND DOLLARS 185