Pigment deficient, transparent shells showing green/turquoise mantle and central, dark, amphora-shape on the shell’s interior.
T. testudinalis feeds on algae coating bedrock and boulders. Eulittoral specimens are often found stationary on bare, vertical or overhanging rock during daylight hours. © P. Lightfoot and B. Hitchin.
APPENDIX re range advance/retreat: flic.kr/p/2jW74ig