Ultrastructure of the epidermal eyespots of an acoel platyhelminth.
The epidermal eyespots of the acoel Otocelis rubropunctata would appear to consist of a single cell type provided with pigment granules and cilia. Very numerous dictyosomes characterize the cytoplasm of the cells. The cilia possess the 9X2 + 2 pattern of microtubules and the typical rootlets of acoels. Microvilli are interspersed among the cilia. The basal surface of the cells seems to present synatpic input and to generate an axonal process, which would confirm their photosensitive role. The structural similarities with other photoreceptors are outlined.
Lanfranchi
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Department of Animal Behaviour and Human Sciences, University of Pisa, via A. Volta, 6, I-56126 Pisa, Italy.