PARTIAL EMERGENCE OF THE BIVALVE DONAX-VITTATUS IN RESPONSE TO ABRUPTCHANGES IN LIGHT-INTENSITY AND BEFORE SPAWNING

Buried individuals of the bivalve Donax vittatus (Bivalvia: Donacidae) respond to change in incident light intensity by adjusting their posi tion in the sediment. Video recordings of activity in aquarium tanks i n natural daylight revealed that individuals responded to shading by m oving upwards, causing some to partially emerge from the sand. Subsequ ent removal of the shading stimulated reburial to the normal position. Recordings in laboratory aquaria show similar upward movement and par tial emergence occurring when illumination in the visible range is swi tched off. Upward movement and partial emergence of D. vittatus has al so been observed to take place prior to spawning.