Effect of microgravity on the development of embryos/larvae and the larvalesophageal musculature of the purple starfish, Pisaster ochraceus

Early gastrula stage embryos of the purple starfish, Pisaster ochraceus, we re raised for 10 days in microgravity (mu G) in an Aquatic Research Facilit y aboard the space shuttle Endeavour (STS 77). Controls consisted of embryo s raised at 1 x g (1G) in flight and embryos raised at 1G on the ground. Ex perimental organisms and controls were fixed on mission days (MD) 3, 4, 5, 6, and 7 and one sample was returned alive. Comparison of the mu G embryos with the 1G in-flight controls and ground controls suggests that there is l ittle difference in size and overall development. Scanning electron microsc opic examination of the development of the esophageal musculature showed th at the pattern of development and differentiation was normal and was the sa me in both the in-flight and ground controls. The esophageal muscle cells o f specimens returned alive after 10 days in mu G contracted normally. Detai led transmission electron microscopic examination of MD 7 embryos revealed a decreased amount of sarcoplasmic reticulum in the mu G embryos compared w ith both MD 7 1G in-flight and ground controls. These results suggest that while exposure to mu G may slow muscle differentiation slightly, it has lit tle overall effect on embryos/larvae of up to 7-8 days of development.