Abstract
The identification and classification of new taxa are crucial for understanding biodiversity. However, assigning samples to new taxa requires cautious and rigorous approaches. Historically, taxonomy has heavily relied on morphological traits, which can be subjective and may not always reflect underlying genetic divergence—particularly in organisms with few diagnostic morphological traits. A prime example is the sponge genus Oscarella (Homoscleromorpha), where species delimitation is challenged by the absence of spicules and limited morphological characters. Here, we address this gap by combining an extensive genetic dataset (192 specimens, five markers) with systematic photographic documentation. This approach enabled a robust assessment of Oscarella diversity in the Western Mediterranean, resulting in the identification of four species new to science. Multigene phylogenetic analyses also enabled us to propose an evolutionary scenario for color polymorphism. Moreover, our data highlighted critical limitations in current methodologies for studying Oscarella, including the low resolution of the widely used cytochrome c oxidase subunit I (cox1/COI) gene, the lack of genetic data for many species, and insufficient information on their geographical distribution. These issues, which mirror challenges across many taxa, highlight the urgent need for standardized genetic frameworks and comprehensive datasets to improve taxonomic resolution for each taxon.
Acknowledgements
Data were generated through the Molecular and Cell Biology Facility of IMBE, Aix-Marseille Univ, Avignon Univ, CNRS, IRD, Marseille. We are grateful to S. Chenesseau from the Morphology Facility of IMBE and to G. Deniel for preparing the semi-thin sections, as well as to the OSU Pytheas diving facility for their support in Oscarella sampling. We also warmly thank A. Baumel for helpful input on manuscript preparation.
Funding
This work was supported by the Mediterranean Institute of Biodiversity and Marine and Continental Ecology (IMBE) through the AOI C-POSCA and the French National Research Agency (ANR) through the JCJC program I_SEA_RAINBOWS (ANR-25-CE02-1622-01).
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Guiollot, E., Guillemain, D., Renard, E. et al. Genetic and morphological insights reveal the hidden and colorful diversity in Oscarella sponges.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-73635-z
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DOI: https://doi.org/10.1038/s41598-026-73635-z
Keywords
- Porifera
- Genetic markers
- Species delimitation
- Taxonomy
- Biodiversity
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