Fig. 2. Transparent windows allow heart cockle shells to transmit 11–62% of photosynthetically active radiation (mean = 31%) and significantly screen out UV radiation (mean = 14%, range = 5–28%).

Here, we measure transmission through intact shells; in Supplementary Fig. 1 we show that individual polished windows transmit 20–55% of light (mean = 37%). a–d White LED lights inside each shell show transmission through the windows on the sun-facing side of the shell. Top row: natural light images; bottom row: lit up from inside. a Corculum lorenzi; (b–d) Corculum cardissa. e The shells’ transmission spectra rise at higher wavelengths for both the sun- and sand-facing sides (gray and black curves, respectively). Here we plot transmission for four shells; see Supplementary Fig. 2 for full results. f Averaging across 300–700 nm, the sun-facing side of each shell has significantly higher mean transmission than the sand-facing side (two-sample two-sided paired t test; p = <0.0005, 95% CI = [11, 19.2], mean diff.= 15.1, df = 10, t = 8.22, Cohen’s d = 3.03). g Shells transmit significantly more long-wavelength red light (600–700 nm) than short-wavelength UV radiation (300–400 nm), particularly on the sun-facing side (two-sample two-sided paired t tests: sun-facing side; p = 0.000012, 95% CI = [17.6, 31.3], mean diff. = 24.4, df = 10, t = 7.98, Cohen’s d = 2.93; sand-facing side: p = 0.000019, 95% CI = [7.79, 12.4], mean diff. = 10.1, df = 10, t = 9.8, Cohen’s d = 3.60). The sun-facing side screens out UV radiation to a significantly greater extent than does the sand-facing side (two-sample two-sided paired t test: p = 0.00035, 95% CI = [8.31, 20.4], mean diff. = 14.4, df = 10, t = 5.29, Cohen’s d = 1.90). Boxplots show median, quartile 1, quartile 3, and whiskers that extend to the largest and smallest values ≤ |1.5 * interquartile range|. The sample size in (f, g) is n = 11 distinct organisms. See Source Data for Fig. 2 in UVVisTransmission_Corculumcardissa_16Mar2022.csv (Supplementary Data 1.zip).