Developmental rate as a functionof depth in the bathyal echinoid Linopneustes longispinus

In the Bahamas, adults of the spatangoid sea urchin Linopneustes longispinus live on sandy bottoms between600 and 700 m depths, where water temperature remains nearly constant at 7.5-8.5°C. Ripe individualswere obtained by submersible during October and November, and gametes were fertilized aboard ship.Embryonic development was similar to that of most shallow-water echinoids; small (109 µm diameter) eggsproduced planktotrophic echinopluteus larvae. Early embryos were transplanted to 4 depths (879 m, 595m, 294 m, 4 m) and incubated in situ for 24 h. These were compared with control cultures held in thelaboratory at comparable temperatures (5, 10, 15, 25 ͦC), Embryonic development proceeded normally tothe blastula stage at the three greatest depths (corresponding to temperatures of 5,10, and 15°C), but embryosdied at higher temperatures, both in the field and the laboratory.