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Molluscs, which include animals like snails, clams, squids, and octopuses, boast extraordinary diversity in shape, size, behaviour and habitat. Despite their ecological and economic importance, their evolutionary relationships have been notoriously difficult to untangle due to conflicting evidence from fossils, physical traits, and genetics.

In their new study, scientists analysed the genomes of 77 mollusc species, representing all eight major living groups, including lesser-known forms like deep-sea monoplacophorans and worm-like solenogasters. Using cutting-edge genomic techniques, the team reconstructed a detailed evolutionary tree and confirmed key hypotheses about mollusc ancestry.

“We can now give you a better picture of the likely ancestor of all molluscs – from your common garden snail to a deep-sea octopus,” said Dr. Zeyuan Chen, first author of the paper and bioinformatician at Senckenberg Research Institute and Natural History Museum Frankfurt, Germany. “This ancestor likely had a hard shell, a foot for movement, no eyes, and a radula – a specialized feeding organ.”

The study confirmed that molluscs split early in their evolution into two main groups called Aculifera and Conchifera. Aculifera includes species with small needle-like spicules and sometimes shells. Conchifera includes the more “traditional” mollusc groups such as snails, clams, and cephalopods. The new findings also resolved a long-standing debate about the evolutionary relationships among certain molluscs. The controversial “living fossil” Monoplacophora (headless molluscs with a cap-like shell) are the earliest branch within Conchifera, followed by cephalopods (squid, cuttlefish and octopus). The other conchiferans form a group that is now named Megalopodifera, or the “big foot molluscs” including the enigmatic scaphopods along with clams and snails and slugs. 

Dr. Chen notes that “Molluscs exhibit high genetic diversity, which can be a challenge in understanding their evolution, but likely explains why they have been so successful in adapting to a range of environments – from deep oceans to dry land.” 

Implications:

“This research provides a foundation for understanding the evolution and biology of one of the most successful animal groups on Earth,” said Prof. Dr. Julia Sigwart, Head of the Malacology Section at Senckenberg Research Institute and Natural History Museum Frankfurt, Germany. “Understanding molluscs helps us begin to answer big questions about how life adapts and diversifies over time.”

Beyond evolutionary insights, the findings have broad implications for fields ranging from environmental science to medicine. Molluscs are essential in marine and terrestrial ecosystems, and some species serve as models for studying human health and disease.

About Molluscs:

Molluscs represent one of the largest and most diverse groups of animals, with over 100,000 known species— and countless more yet to be discovered. From microscopic bivalves to giant squids, common garden slugs to hydrothermal vent snails clad in iron scales, these incredible creatures thrive in a vast range of habitats—from deep sea, coasts, freshwater, and terrestrial landscapes.

Future Directions:

The research team hopes to expand their work by analysing more species and exploring how genetic diversity has driven mollusc innovation. The study also opens the door for applications in biotechnology and conservation.

Publication: Zeyuan Chen et al. (2025): A genome-based phylogeny for Mollusca is concordant with fossils and morphology. Science. https://www.science.org/doi/10.1126/science.ads0215