The mantle secretes an organic matrix and various crystalline forms of calcium carbonate to form the shell. On T. testudinalis the mantle is translucent and colourless but covered with a dense layer of removable pigment of emerald green apart from a peripheral mustard-brown border.
1: mustard border of mantle skirt that secretes the external shell layer and the internal aperture rim (zone M+2).
2: green mantle skirt between the mustard border and white pedal retractor muscle. The skirt roofs the pallial groove, and secretes the white interior layer of shell in that area (M+1).
3: inner edge of 2, line of mantle attachment to shell.
4: narrow, white U-shape, pedal retractor muscle that leaves a clear slightly glazed scar on the shell (M).
5: amphora shaped mantle, within the outline of the pedal retractor muscle, which secretes the chocolate brown interior shell-layer (M-1).
6 less heavily pigmented area of amphora, roofing the mantle cavity, that secretes the cream to pale brown interior layer near the vertex of the shell (M-2).
See image 16 Testudinalia testudinalis. Length 14.1mm. Littoral. Moray Coast, Banffshire, Scotland. May 2017. Leg. S. Taylor. for corresponding shell zones.
See image 17 Testudinalia testudinalis. Shell length 14.1mm. Littoral. Moray Coast, Banffshire, Scotland. May 2017. Leg. S. Taylor. for closer view of shell and mantle.
For explanation of zone numbering and structure, ‘M+2’ etc., see account and images at flic.kr/s/aHskjiP2GM
APPENDIX re range advance/retreat: flic.kr/p/2jW74ig