Left: disarticulated opercular valves (treated with bleach). Different faces of right tergum 1, 3 and scutum 2, 4. Face 2 and part of 1 visible on live animal (spur on 1 projects up). Barnacle diameter 19mm. Menai Strait. March 2012.
Right: articulated opercular valves. Live, but shell wall broken so position in life exposed, tergum 5 and spur of tergum 6. Menai Strait, Wales. July 2013′
Opercular plates on specimens over 20mm diameter are often heavily eroded, and the tergal beak may be broken off.