Summary
The structure of the ocelli of the interstitial gastropod Fartulum orcutti was studied using light and electron microscopy. Each eye is composed of pigmented, rhabdomeric, and ciliated cells. The pigmented cells contain many electron-dense granules and form a cup that shades the sensory cells from all light except that entering from a dorsal-anterior direction. The rhabdomeric cells are similar to the photosensory cells described for other gastropods. They contain photic vesicles and are characterized by an array of microvilli that project into the interior of the eyecup. In the ciliated cells, the ciliary membranes are greatly expanded and form whorls that lie at the front of the eye, opposite the pigment cup. Axons from the bases of rhabdomeric cells have been traced into the optic ganglion, whereas nerve connections from the ciliated cells have not been observed. We suggest that both the rhabdomeric and ciliated cells are photosensory based on their morphological similarities to eyes in other invertebrates. The significance of ocelli with two types of sensory cells is discussed with regard to 1) phylogenetic schemes based on photoreceptor morphology, and 2) the function of such eyes in the interstitial habitat. In addition, the structure of the eye in Fartulum is compared with the description at the light microscopical level of the eye of a related interstitial gastropod.
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Howard, D.R., Martin, G.G. Fine structure of the eyes of the interstitial gastropod Fartulum orcutti (Gastropoda, Prosobranchia). Zoomorphology 104, 197–203 (1984). https://doi.org/10.1007/BF00312031
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DOI: https://doi.org/10.1007/BF00312031