Does the pedicle exist in craniiform brachiopods?

Abstract Although Brachiopoda represent a relatively small phylum, they exhibit significant morphological diversity. One of the central issues in understanding the evolution of the ancestral brachiopod body plan pertains to the homologies among body compartments across the different brachiopod subphyla: Craniiformea, Linguliformea, and Rhynchonelliformea. In this context, the pedicle stands out as one of the most contentious organs, characterized by differing origin and organisational aspects among various brachiopod taxa. In this study, we present original observations of Novocrania anomala and Lingula anatina to explore the prevailing hypotheses regarding pedicle evolution in brachiopods, notably the hypothesis of convergent evolution and the ‘anal papilla hypothesis’. Our findings indicate that N. anomala possesses a prominent posterior outgrowth of the soft body that contains the coelomic cavity, which is lined by myoepithelium. This organizational structure shares many similarities with the well-developed pedicle found in L. anatina, suggesting that the posterior outgrowth of N. anomala may be homologous to the pedicle of other brachiopods. Therefore, it is likely that representatives from all three subphyla of brachiopods possess pedicles that were inherited from their last common ancestor, subsequently undergoing remodelling in distinct lineages in various ways.