The Cretaceous acorn barnacle Archaeochionelasmus nekvasilovae Kočí, Newman and Buckeridge, 2017 (Cirripedia, Neobalanomorpha) is a fragmentary rudist (Bivalvia, Mollusca)

The unique holotype of Archaeochionelasmus nekvasilovae Kočí, Newman and Buckeridge, 2017, from the upper Cenomanian of the Czech Republic, supposedly an early neobalanomorph belonging to the extant family Chionelasmatidae, is compared in detail with chionelasmatids and rudist bivalves. The morphology and shell structure demonstrate that, rather than being a barnacle, it is a poorly preserved fragment of a rudist, which roughly mimics the form of an incomplete balanomorph wall.