Left: length 4.6mm. littoral.
Juvenile (GS3) on exterior of Laminaria holdfast. At 4.6mm length, it may still be possible for it to squeeze between the tendrils into the holdfast, but it becomes increasingly difficult and very few over 6mm manage to enter.
Juveniles rarely, if ever, have any epibiotic growths on the smooth shell.
Through the almost transparent shell can be seen:
1: darker central mantle covering viscera.
2: the white, horseshoe shaped, pedal-retractor muscle.
3: the chestnut band on the distal face of the pedal-retractor muscle.
4: the white, peripheral, pallial gills.

Right: length c. 2 to 3mm. Shallow subilttoral; 2 or 3 metres depth.
Juveniles recently moved from encrusting calcareous algae (many GS2 close by still on it) onto Laminaria and starting to grow larger less pear shaped GS3 juvenile shells.

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.