Anteriors at top of image. Three images of same specimen:
Left; live in water soon after capture. Coated with thin layer of yellowish alga. Fine radiating ridges clearest on this view.
Centre; recently dead, in water, after other specimens in captivity had grazed off algal coating.
Right; dead and dry. Colours duller but growth lines more distinct on dry specimen.
Superficially smooth, but major growth lines, and many finer ones, run concentrically around the shell; spacing between them is closer on the anterior as growth is more rapid at the posterior.
Many fine ridges radiate from the apex. The visibility of the radiating lines and growth lines of an individual shell varies with its history and the viewing conditions.
APPENDIX re range advance/retreat: flic.kr/p/2jW74ig