Phototaxis and Thermotaxis in Some Species of Amphistegina (Foraminifera)

Positive phototaxis was demonstrated in specimens of Amphistegina radiata within the range of photonic fluxes of 10¹¹ to 10¹⁵ photons × cm^‐2× sec^‐1. No response was found at lower intensities. Amphistegina radiata has a Dartnall nomogram‐shaped action spectrum with a peak at ∼500 nm. In addition, A. radiata and A. madagascariensis, which had been maintained at 18 C, moved toward higher temperatures in a horizontal temperature gradient in total darkness. Amphistegina radiata and A. madagascariensis did not move at temperatures ≤ 12 C and ≤ 16 C respectively. An equal number of specimens moved toward the higher and lower temperatures in the gradient when A. radiata was placed at ∼29 C and A. madagascariensis at ∼22 C. The roles of light and temperature in the distribution of the genus Amphistegina in nature are discussed.