A fleshy flap, tergoscutal flap, runs along the free edge of the tergum and scutum on each side of the opening of the operculum. The carinal plate and terga are all on the right in the above images.
From top left to bottom right, the species are: 1 Chthamalus stellatus, 2 Chthamalus montagui, 3 Austrominius modestus, 4 Semibalanus balanoides, 5 Balanus balanus, 6 Balanus crenatus, 7 Amphibalanus improvisus and 8 Perforatus perforatus.

Full INTRODUCTION TEXT at 01 Barnacle Introduction
Albums with full accounts of all British acorn barnacle species at marinvert.senckenberg.science/image-browse/7215763361…