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Species of the family Ovulidae Fleming, 1822 are sometimes mistaken for seaslugs, especially when the shell is covered by the large colourful mantle. Let me quote Bill Rudman:
"One easy way to separate snails from slugs is to look for their eyes. If they are raised from the skin like this then they are a snail. If the eyes are embedded in the skin they are an opisthobranch."
How to cite:
Köhler, E. (2017), published 1 October 2017, Diminovula culmen (Cate, 1973)
available from https://www.Philippine-Sea-Slugs.com/Look-alike/Ovulidae/Diminovula_culmen/Diminovula_culmen.htm