EMBRYONIC THERMOSENSITIVITY OF THE ASCIDIAN, CIONA-SAVIGNYI

Embryonic temperature sensitivity of the solitary ascidian, Ciona savi gnyi, was examined with special reference to acclimatization to season al 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 f or development from early cleavage stage to metamorphosis in embryos p roduced by individuals raised in warmer seasons differed significantly from that of individuals raised in colder seasons. Within the common optima! temperature range, developmental times at any given temperatur e were the same for both groups of embryos. The thermal acclimation of ascidian embryos is discussed and compared with that of echinoid embr yos.