Figure 1. Spine-associated bioluminescent display.

(a) Location of mineralized finspines in an adult Etmopterus spinax specimen. (b) Close-up of first dorsal spine with SAPs in natural light. (c) Close-up of second dorsal spine with spontaneously glowing SAPs in darkness. (d) Spontaneous luminescence from another specimen of this species showing the glowing dorsal SAPs (white circles), counterilluminating ventral photophores¹⁴ (CVPs) and lateral photophore areas believed to be involved in intraspecific communication¹⁵,¹⁶: ca, caudal; ic, infracaudal; la, lateral; pe, pectoral. Scale bars, 5 cm.