The structure of scale lens and inner reflector in the photophore of the deep-sea fish Neoscopelus microchir (Myctophiformes: Neoscopelidae): insights into the light projection mechanisms for counterillumination

Author(s)

Paitio, Jose ; Yano, Daichi ; Asada, Hironori ; Iwasaka, Masakazu ; Takei, Shiro ; Oba, Yuichi

• Document type: Journal article
• Source: ZOOMORPHOLOGY; v. 144, n. 2, p. 14-pg., 2025-08-01.

Abstract

Myctophiformes is composed of two families of deep-sea fishes, Myctophidae and Neoscopelidae, which probably share a common bioluminescent ancestor. Fishes from each family employ different mechanisms to manipulate light within their photophores, with Myctophidae utilizing a colored reflector and Neoscopelidae a pigmented filter. In Myctophidae, the small area of the scale on the photophore is thick thus suggesting its dioptric property and called scale lens. In this paper, we describe similar scale lens structure and a specialized ultrastructure of the inner reflector in Neoscopelus microchir, providing insights on the light projection mechanism of Neoscopelidae photophores. The silver inner reflector has a parabolic-like shape and is comprised of guanine crystals averagely parallel to the reflector surface, projecting light ventrally for counterillumination. The crystals are arranged in two layers with distinct ultrastructure and arrangement of iridophores. Photophore scales feature a transparent window at the center which covers the photocytes, and a light reflector at the periphery. The central area exhibits an increased number and thickness of collagen layers, forming a "lens-like thickening". The scale lenses seem adapted to transmit light from the photophore below, the fusion of collagen layers found in the emission area is accompanied by higher light transmission, suggesting a dioptric function. (AU)

• FAPESP's process: 22/01463-3 - Evolution and biological function of fluorescent filters in the photophores of dragonfishes (Teleostei: Stomiiformes)
• Grantee: José Rui Lima Paitio
• Support Opportunities: Scholarships in Brazil - Post-Doctoral