Fig. 3

Identification of sPhC lattice symmetries in diatoms. (A) Illustration defining the directions along the expected pore symmetries in diatom girdles, which resemble sPhCs. This lateral pore arrangement has been previously identified in the species Coscinodiscus granii⁸ and was used to develop the model for characterizing sPhCs in this study. The internal pore system, as indicated in this computer-aided design, has a minor impact on the spectral position of the photonic stopband and was therefore not considered in the numerical analysis⁸. (B) Example of a square lattice sPhC identified in this dataset, as seen e.g. in the species C. granii. (C) Example of a hexagonal lattice sPhC, as observed e.g. in the species Trieres mobiliensis. (D) The number of pores in the z-direction significantly influences the reflectance intensity of the stopband. Our numerical analysis indicates that a minimum of 15 pores (N) in z-direction is necessary to observe stopband reflectance. Consequently, candidates with symmetrical pore symmetries having fewer than 15 pores were classified as quasi-crystals, as they lack the periodicity required to open a photonic band in z-direction.