Drupa arachnoides (Lamarck, 1816)
24.1mm

Drupa arachnoides is generally considered a synonym or subspecies of Drupa ricinus. The differences between the two, at least among Kwajalein specimens, is that D. arachnoides has orange dashes around the perimeter of the glossy white aperture, which are lacking in D. ricinus, except perhaps for light orange patches near the anterior siphon. Also, D. arachnoides tends to have longer spines, but that may be due to the third, and to me the most important difference. D. arachnoides is found subtidally, under rocks but also in seaward caves and ledges at depths of up to 20m at least. Shells that look more like D. ricinus live intertidally or on shallow subtidal reefs. From what I have seen, they do not appear to overlap in habitat. While they may well be the same species with different forms depending on where they settle out, I consider it best to leave them separate until someone has the inclination to compare their DNA.

With an egg mass.

Created 5 October 2017

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