† ORDER BALANOMORPHA PILSBRY, 1916

Diagnosis: Monophyletic in molecular analyses. A peduncle is absent at all stages of development; shell wall made up of four to eight plates, plesiomorphically comprising rostrum, carina, rostromarginals, marginals and carinomarginals.The body is covered by an operculum formed by the paired scuta–terga; the operculum articulates with the wall plates and forms a watertight cover over the mantle cavity. The structure of the wall plates and articulation with the basis is often complex in more derived balanomorphs; the apicobasal (longitudinal) septa are composed of a frond-like array of calcite crystals in cross-section, called an interlaminate figure.

Comment: In some forms, the wall is surrounded by one or more whorls of small-sized imbricating scales, as also seen in the Brachylepadomorpha .