Supplementary figure s4 from Deep-sea starfish from the Arctic have well-developed eyes in the dark

Structure of the ommatidia. Light microscopical (LM) and transmission electron microscopical (TEM) sections were obtained from five species of special interest: Pteraster pulvillus (A, B, C), Hippasteria phrygiana (D, E, F), Lophaster furcifer (G, H, I), Novodinia americana (J, K, L), Diplopteraster multiples (M, N, O). It is seen that H. phrygiana and N. americana have long and slim ommatidia similar to A. planci whereas the three other have much wider ommatidia. The angles shown in A, D, G, J, and M are defined by the centre of the OS and edge of the screening pigment and are proxies for the acceptance angles of the ommatidia. Note the higher membrane density in the outer segments (OS) of L. furcifer and N. americana indicating enhanced sensitivity. C, F, I, L, and O show synapses with dense core vesicles (arrows) documenting the similar and in general high quality of the fixation in all 5 species. SP=screening pigment.