Figure 2. Physical characteristics of shark luminescence.

(a) Photophore density maps from the dalatiid S. aliae and the etmopterid E. splendidus (horizontal dashed lines indicate anterior and posterior wholemount connections with adjacent low-density artefact) with associated in vivo luminescence and transverse angular distribution (blue vectors indicate the intensity of luminescence in selected directions). Bs, body section at 0.5 prepelvic length. Luminous zone abbreviations same as in Fig. 1. Scale bars, 2 cm. (b) Dalatiid and etmopterid emission spectra (new data combined with published spectra¹⁸,³¹) compared to published peak emission wavelength of mesopelagic coastal¹⁸ and oceanic³² waters: 1, I. brasiliensis (λ_max = 455 nm); 2, S. aliae (λ_max = 457 nm); 3, E. splendidus (λ_max = 476 nm); 4, E. molleri (λ_max = 477 nm); 5, E. spinax (λ_max = 486 nm). Photographs by Mallefet. Drawings by Claes.