Modulatory effects of some amino acids and neuropeptides on luminescence in the brittlestar amphipholis squamata   Amphipholis squamata is a polychromatic luminescent ophiuroid. The effects of amino acids ( &ggr; -aminobutyric acid, GABA, taurine, glycine and glutamate), N-methyl-d-aspartate (NMDA) and the invertebrate neuropeptides Antho-RFamide, FMRFamide and SALMFamides S1 and S2 were tested on acetylcholine-induced luminescence from isolated arms of clear and black specimens of Amphipholis squamata. The results showed that GABA, glycine and Antho-RFamide inhibited ACh-induced luminescence of clear specimens and had no significant effect on black specimens. Glutamic acid had no significant effect on ACh-induced luminescence, but triggered luminescence in the absence of ACh in both types of specimen. Taurine, NMDA and FMRFamide showed no significant effects on either clear or black specimens. S1 potentiated ACh-induced luminescence of clear and black specimens, while S2 had no clear modulatory effect on luminescence. These results suggest that, in addition to the previously described cholinergic system in Amphipholis squamata, there is also a modulatory component to luminescence control. Moreover, we observed a difference in modulation of luminescence between clear and black specimens.