A story of Neomicrorbis: a widely distributed bathyal serpulid long hidden in museum collections

Abstract Neomicrorbis Rovereto, 1903 is a serpulid taxon well represented in the Cretaceous and Tertiary fossil records and described as the bathyal extant species Neomicrorbis azoricus Zibrowius, 1972. This enigmatic species of uncertain taxonomic affinities exhibits a morphology intermediate between serpulids sensu stricto (Serpulinae and Filograninae) and Spirorbinae. Only recently the phylogenetic placement of these unique serpulids has been clarified, unequivocally positioning them as the sister group to all other Spirorbinae. Despite this advancement, most aspects of their biology, distribution, and even morphology remain largely unexplored. We provide detailed morphological descriptions of specimens from the Azores (type locality) in the Atlantic, as well as from the Indian and the Pacific Oceans, using both long-hidden material in museum collections and recently collected specimens. This study enhances the original description of N. azoricus , which was based on a single, poorly preserved juvenile specimen, by offering a comprehensive overview of the species’ morphology. Our analysis utilizes advanced imaging techniques such as scanning electron microscopy, microCT, and 3D visualization. Contrast-enhanced microCT scanning has proven exceptionally valuable for non-invasive visualization of the worms within their calcareous tubes. This method shows great promise for studying serpulids in natural history collections. Our findings reveal a remarkable morphological consistency across specimens from geographically remote regions, suggesting a wide distribution for the species. However, molecular data on Neomicrorbis are currently limited to recently collected specimens from the Indian Ocean. Further genetic studies are necessary to fully understand the population structure and genetic diversity of Neomicrorbis azoricus across its range.