Tectura virginea for comparison.
Shell exteriors whitish (top image) and bluish, with light-brown chains and, peripherally, radiating pinkish rays.
1: cephalic tentacles, slightly wrinkled as not fully extended.
2: snout.
3: outer lip expanded as translucent oral veil on substrate; contains many sensory structures; possible functions to detect Lithothamnion, locate mouth precisely to avoid overlap with previous feeding pit without missing part of food, and to retain loose fragments (function of anterior scraper-jaw on Patella spp.; missing from T. virginea).
4: side of foot lacks epipodial tentacles.
5: edge of mantle-skirt white with reddish bands that produce corresponding rays of shell.
APPENDIX re range advance/retreat: flic.kr/p/2jW74ig