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 not distinct because central area eroded.
On this specimen, central area is eroded and thinner, so more translucent, revealing shadow of dark brown interior. Also, radiating ribs are indistinct near the apex.
APPENDIX re range advance/retreat: flic.kr/p/2jW74ig