Anterior bundle (1) of horseshoe-shaped series forming the strong pedal-retractor muscle. Distal face (2) of pedal-retractor muscle is white, as usual for adult holdfast dwellers.
Anterior dorsal surface of the foot, below the head (3), is yellowish with brown creases. This colouration extends faintly over much of the foot dorsally (4).
The lateral glandular streak has an overhanging upper lip (5) which is usually paler than the rest of the foot when the latter is tinted yellowish. Sediment in inhalant water is trapped by mucus from the lateral glandular streak and carried forwards and out by the exhalant current along the pallial groove.
There is a red osphradium (6) in the nuchal cavity next to each terminal bundle of the pedal-retractor muscle. It is unlikely that they test the quality of inhalant water as there are no associated ctenidia to forwarn, and they are located in the path of the exhalant water after it has flowed over the pallial gills and shortly before it exits the anterior of the shell. There are anatomical signs that they may be vestiges of a lost double osphradium-ctenidium complex like that still found in Diodora graeca 20 Diodora graeca (Spengel, 1881, in Fretter & Graham, 1962, p314).

Concise
Part 1, SHELL FORMS: 02 Patella pellucida. Growth Stage 2 (GS2). July 2012. Littoral. North Yorkshire, England. © P. Lightfoot.
Part 2, BODY & ANATOMY: 03 Patella pellucida. Growth Stage 3 (GS3). 2009. Sublittoral, Farne Islands, Northumberland, England. © P.Lightfoot.
Part, 3 HABITS & ECOLOGY: 04 Patella pellucida. Length 4.6mm. Growth Stage 3 (GS3). September 2016. Yorkshire, England. © P.Lightfoot.