An international team of researchers has resolved long-standing questions about the evolutionary history of mollusks, one of the most diverse and ecologically significant groups of animals on the planet. The new study, published in Science, reconstructs the mollusk family tree using genome-based data and provides fresh perspectives on how these animals evolved over time.
Professor Juan Moles, a prominent researcher from the Faculty of Biology and the Biodiversity Research Institute (IRBio) of the University of Barcelona, is the only expert from a Spanish institution to participate in this groundbreaking research. His contribution, alongside scientists from around the world, helps clarify scientific debates that have persisted for decades about the evolutionary relationships of mollusks.
The Mollusk Diversity Puzzle
Mollusks are an incredibly diverse group of organisms that can be found in almost every type of ecosystem on Earth. From microscopic bivalves living in freshwater lakes to giant squids deep in the ocean, mollusks are incredibly adaptable. Their ability to thrive in a vast array of habitats—from seabeds and coastal areas to freshwater ecosystems and even dry terrestrial environments—makes them one of the most ecologically significant groups in the animal kingdom.
As of now, scientists have described nearly 100,000 mollusk species, with many more yet to be discovered. These creatures exhibit extraordinary diversity in terms of body size, shape, behavior, habitat, and genetics. Despite this immense diversity, the evolutionary relationships among these creatures have been difficult to discern due to conflicting evidence from fossil records, morphological studies, and genetic data.
This new study, which includes the analysis of 77 mollusk species representing eight major groups from around the world, provides a clearer understanding of mollusk evolution, offering new answers to long-debated questions.
The Genomic Approach: A New Window into Mollusk Evolution
The team’s breakthrough came from analyzing the genomes of these diverse mollusk species. By looking at the genetic material from a wide range of mollusks—including lesser-known forms like the deep-sea monoplacophorans and solenogastropods (worm-like mollusks)—the team was able to piece together a more accurate picture of the mollusk family tree.
The results of the study present a genome-based phylogeny of the phylum Mollusca that not only aligns with the fossil record and morphological studies but also confirms the ancestry of mollusks with greater precision. According to Zeyuan Chen, the first author of the study and a bioinformatician at the Senckenberg Research Institute in Germany, this new phylogeny helps answer important questions about the evolutionary origin of mollusks.
“We can now provide a clearer picture of the probable ancestor of all mollusks, from the garden snail to a deep-sea octopus,” Chen explains. “This ancestor probably had a hard shell, a foot for movement, no eyes, and a radula—a specialized organ used for feeding.”
Key Findings: Unraveling the Ancient Lineages of Mollusks
One of the most significant revelations from this study is the confirmation that the mollusk lineage split early in evolutionary history into two major groups: Aculifera and Conchifera. These two groups represent different evolutionary pathways and contain many of the familiar mollusk species we know today.
- Aculifera includes species with small, needle-like spicules and, in some cases, shells.
- Conchifera, on the other hand, encompasses more traditional mollusks, such as snails, clams, and cephalopods (including squids, cuttlefish, and octopuses).
The study also addresses a long-standing debate about the evolutionary relationships of certain mollusks, particularly monoplacophorans. These “living fossils,” once thought to be extinct, were considered to be among the most primitive forms of mollusks. The new study reveals that monoplacophorans are the oldest branch within Conchifera, making them a key evolutionary group within the mollusk family tree.
Following the monoplacophorans are the cephalopods, which evolved from early mollusks that possessed a hard shell but later adapted to live without it, ultimately developing complex nervous systems and behaviors.
The rest of the Conchifera group, now classified as the Megalopodifera (meaning “big-foot bearing”), includes familiar mollusks like scaphopods (tusk shells), clams, snails, and slugs. These mollusks, with their distinct foot structures, evolved different ways to adapt to various environmental challenges over millions of years.
Mollusk Adaptation: Why Are They So Successful?
One of the most fascinating aspects of the mollusk group is their extraordinary adaptability. With nearly 100,000 species already cataloged, and countless more potentially undiscovered, mollusks have proven to be one of the most evolutionarily successful groups of animals on Earth. The study suggests that this success is likely due to the high genetic diversity within the phylum. This diversity has enabled mollusks to exploit a wide range of ecological niches, from deep-sea environments to dry continental ecosystems.
Zeyuan Chen explains, “Mollusks have a high genetic diversity, which can be a challenge to understand their evolution, but probably explains why they have been so successful in adapting to various environments, from deep oceans to dry continental environments.”
Implications for Biotechnology and Conservation
Beyond offering insights into the evolutionary biology of mollusks, this research has the potential to benefit several areas of biotechnology and conservation. Some mollusk species are already used as models for studying human health and disease, particularly in fields such as neurobiology, regeneration, and biomedicine. Understanding mollusk genomics can also help scientists develop new technologies in biomaterials, as certain mollusks, like mussels, produce incredibly strong adhesives that have inspired synthetic materials.
Furthermore, this research could have significant applications in environmental science. Mollusks play vital roles in ecosystems as filter feeders, helping to maintain water quality in aquatic environments. They also serve as important bioindicators, offering clues about the health of ecosystems, especially in the face of climate change and pollution.
Professor Juan Moles, from the University of Barcelona, notes that this new research is critical in understanding the broader questions about how life on Earth has adapted and diversified over time. “Understanding mollusks helps us to start answering big questions about the evolution of life and how different organisms have adapted to the ever-changing conditions on Earth.”
Looking Ahead: Expanding Our Knowledge
While this study has provided significant insights into the evolutionary history of mollusks, the research team is not stopping here. They plan to extend their studies by analyzing additional mollusk species to further investigate how genetic diversity has driven evolutionary innovation within the phylum Mollusca.
The team’s future efforts will likely involve exploring the complex genetic networks that have shaped mollusk biology over millions of years. This could help uncover even more about their evolution and how their unique traits—such as their ability to adapt to extreme environments—have allowed them to thrive in some of the most challenging habitats on Earth.
Conclusion
The groundbreaking work of this international research team marks a new era in our understanding of mollusks. By combining advanced genomic analysis with traditional methods of studying morphology and fossils, scientists have successfully reconstructed the family tree of one of Earth’s most diverse and successful animal groups. The study not only provides crucial insights into the evolutionary history of mollusks but also opens the door for new applications in biotechnology, conservation, and medicine.
As researchers continue to explore the genetic diversity within the mollusk phylum, they are likely to uncover even more secrets about these fascinating creatures and their incredible ability to adapt and survive in a constantly changing world.
Reference: Zeyuan Chen et al, A genome-based phylogeny for Mollusca is concordant with fossils and morphology, Science (2025). DOI: 10.1126/science.ads0215