Summary
A fine structural investigation was performed on receptor cells lying at the base of the epidermis in the earthworm, Lumbricus terrestris. Two types of receptor cells with many similarities, but also with major differences, were discriminated.
One receptor is of the microvillar receptor type, that appears to be identical with the photoreceptor cell described earlier by Röhlich et al. (1970). Proximal to the nucleus is a large vacuole (phaosome, “Binnenkörper”) with many daughter cavities containing a large number of microvilli and several cilia with the 9 × 2 + 0 microtubular pattern. The intracellular cavity has no connection with the surface membrane, in contrast to that in hirudineans (White and Walther, 1969) and pogonophores (Nørrevang, 1974).
The other receptor is the ciliated receptor type, that is presently described for the first time. This receptor also has a comparatively large uniform cavity, few microvilli and about 20 cilia with the 9 × 2 + 2 microtubular pattern. The cilia leave the cell in the proximal part through a wide opening, make a turn of 180 °, and proceed toward the epidermal surface. Receptors of a similar type have been described by Golding and Whittle (1975) in the cerebral ganglion of four limicole oligochaete annelids; they presumed that these cells have an osmoreceptor function. The new epidermal receptor type described in the present investigation probably has a chemoreceptor function of hitherto unknown kind.
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This investigation was supported by the Royal Physiographic Society at Lund, Sweden. The author would like to express his thanks to Mrs. Lena Sandell for skilful technical assistance
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Myhrberg, H.E. Fine structural analysis of the basal epidermal receptor cells in the earthworm (Lumbricus terrestris L.). Cell Tissue Res. 203, 257–266 (1979). https://doi.org/10.1007/BF00237240
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DOI: https://doi.org/10.1007/BF00237240