1: respiratory siphon.
2: cephalic tentacle.
3: ventral mid-line where opening to pouch containing feeding proboscis is located.
4: bilaminate anterior edge of foot; contains anterior pedal gland with mucus to lubricate travel.
5: yellow opening to pouch containing female’s ventral pedal gland.
6: opening to pouch containing female’s ventral pedal gland; foot folded up at right-angle in front of gland to position it on a leading edge for action.
7: ventral pedal gland protruded; about to shape egg capsule (8) deposited in hole bitten into compound ascidian prey, Diplosoma listerianum.
For further detail see  25 Trivia arctica and  21.1 Trivia arctica

Left and centre: Height (longest shell-dimension) 9.4 mm. Menai Strait, Wales. March 2014.

Right: 5 m depth, Zierikzee, Netherlands, March 2017, © S. Verheyen.