Embryonic Thermosensitivity of the Ascidian, Ciona savignyi

Embryonic temperature sensitivity of the solitary ascidian, Ciona savignyi, was examined with special reference to acclimatization to seasonal change in seawater temperature. This ascidian spawns throughout the year; its life span is completed within six months and depends on the cumulative environmental temperature. The optimal temperature range for development from early cleavage stage to metamorphosis in embryos produced by individuals raised in warmer seasons differed significantly from that of individuals raised in colder seasons. Within the common optimal temperature range, developmental times at any given temperature were the same for both groups of embryos. The thermal acclimation of ascidian embryos is discussed and compared with that of echinoid embryos.