Spectral sensitivity of the common prawn, Palaemonetes vulgaris.

The vision of Palaemonetes is of particular interest in view of extensive studies of the responses of its chromatophore systems and eye pigments to light. The spectral sensitivity is here examined under conditions of dark adaptation and adaptation to bright colored lights. In each case the relative number of photons per one-fiftieth sec flash needed to evoke a constant peak amplitude (usually 25 or 50 microv) in the electroretinogram (ERG) was measured at various wavelengths throughout the spectrum. The sensitivity is the reciprocal of this number. In dark-adapted animals the spectral sensitivity curve consists of a broad, almost symmetrical band, maximal at about 540 mmicro, with a shoulder near 390 mmicro. Adaptation to bright red or blue light, left on continuously throughout the measurements, depresses the 540 mmicro peak without notably changing its shape or position, implying that only one visual pigment operates in this region. Adaptation to red light, however, spares a violet-sensitive system, so that a high, narrow peak at 390 mmicro now dominates the spectral sensitivity function. The 540 and 390 mmicro peaks are apparently associated with different visual pigments; and these seem to be segregated in different receptor systems, since the associated ERG's have markedly different time constants. It is suggested that these two sensitivity bands may represent the red- and violet-sensitive components of an apparatus for color differentiation.