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Gosliner, T.M., Behrens, D.W. & Williams, G.C. (1997) Coral Reef Animals of the Indo-Pacific. 314pp.
Monterey, California: Sea Challengers.
It is there at page 136 as Delonovolva formosa (Adams & Reeve, 1848), I changed the genus and the authority according to WoRMS.
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 3 August 2017, Cuspivolva formosa (G.B. Sowerby II in A. Adams & Reeve, 1848)
available from https://www.Philippine-Sea-Slugs.com/Look-alike/Ovulidae/Cuspivolva_formosa/Cuspivolva_formosa.htm