The problem of ‘shadow species’ as illustrated with the taxonomic hotchpotch Cyphoderia ampulla (Rhizaria: Cyphoderiidae)

Abstract

Abstract Accurate species delimitation based on an integrative approach is indispensable for biodiversity evaluation. Accordingly, species that were formerly only described morphologically often need to be split into several evolutionary independent units. However, taxonomic actions often lag behind, even when the required data are already available. As a result, invalid species names are carried over the years, with negative implications on ecology, biogeography, and conservation; we designate these entities as ‘shadow species’. This is particularly common in protists, due to the lack of specialized taxonomists and the difficulties of working with microscopic organisms. Here, we resolve the case of the testate amoeba shadow species Cyphoderia ampulla (Rhizaria: Cercozoa: Euglyphida: Cyphoderiidae), a known polyphyletic taxon. Purposely, we integrated the current ecological, genetic, and morphological data on the family Cyphoderiidae with its described evolutionary history. Subsequently, we took the required taxonomic actions to resolve the taxonomy of the family, erecting four new genera (Psammoderia gen nov., Knarr gen. nov., Ichthyosquama gen. nov., and Oleiformis gen. nov.), emending Cyphoderia and describing four new species (Ichthyosquama sanabriensis sp. nov., Ichthyosquama catoirensis sp. nov., Ichthyosquama loricaria sp. nov., and Oleiformis carmelae sp. nov.). Finally, we discuss the extension and relevance of the ‘shadow species’ issue in eukaryotic taxa, and differentiate it from species complex concept.