The acorn barnacle, Chthamalus stellatus

Note the kite shaped opening and the horizontal suture meeting

the vertical suture more or less at right angles. This species could be

confused very easily with its close relative C. montagui, and quite easily

with another relative Semibalanus balanoides.

It is very important when doing distribution work on a rock shore to be

able to distinguish the Chthamalus and Semibalanus genera. Help is given

here where the two species are compared.