In terrestrial pulmonate gastropods, eye spots are present at the tips of the tentacles in the Stylommatophora or at the base of the tentacles in the Basommatophora. These eye spots range from simple ocelli that cannot project an image (simply distinguishing light and dark), to more complex pit and even lens eyes. Vision is not the most important requirement in terrestrial gastropods, because they are mainly nocturnal animals.
Some gastropods, for example the freshwater Apple snails (family Ampullariidae) and marine species of genus Strombus can completely regenerate their eyes. The gastropods in both of these families have lens eyes.
Morphological sequence of different types of multicellular eyes exemplified by gastropod eyes:
Drawing of cross sections of the extracted tentacle (left) and constricted tentacle (right) with and eye of Helix pomatia.
1 - nerve of an eye
4 - eye
5 - tentacle ganglion
6 - epidermis
8 - nerve of an tentacle
9 - retractor muscle
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