Genomes Reveal the Ancient Ancestor of Your Garden Snail
For centuries, the origins of molluscs—one of the most diverse and enigmatic groups of animals on Earth—have puzzled scientists. From microscopic bivalves to giant squids, these creatures have flourished in nearly every corner of the planet. But their evolutionary history remained elusive, obscured by gaps in the fossil record, genetic mysteries, and conflicting physical traits.
Now, an international team of scientists has finally unravelled the long-debated family tree of molluscs, bringing long-sought clarity to their ancient origins. Their ground-breaking study, published in Science, used cutting-edge genomic techniques to trace the ancestry of these extraordinary creatures, resolving disputes that have persisted for decades.
At the heart of the research was an ambitious undertaking: sequencing and analysing the genomes of 77 mollusc species, spanning all eight major living groups. Among them were well-known members like squids, clams, and snails, but also lesser-known species—deep-sea monoplacophorans, mysterious worm-like solenogasters, and scaphopods with their tusk-like shells. By piecing together these genetic blueprints, the researchers reconstructed a detailed evolutionary tree, revealing once-hidden truths 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, lead author of the study and a 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 research confirmed that early in their evolution, molluscs diverged into two main branches: Aculifera and Conchifera. Aculifera includes creatures with small needle-like spicules and sometimes shells, while Conchifera encompasses the more recognizable mollusc groups—snails, clams, and the intelligent cephalopods like squid and octopuses.
One of the most significant findings put an end to a longstanding debate over the placement of monoplacophorans—odd, cap-shaped molluscs often called “living fossils.” The study revealed that these creatures were the earliest branch of Conchifera, followed by cephalopods (squid, cuttlefish and octopus). The other conchiferans formed a newly named group, Megalopodifera, or “big foot molluscs,” which includes clams, scaphopods, snails, and slugs.
Dr. Chen emphasized that the high genetic diversity of molluscs has been both a challenge and a key to their evolutionary success. “It’s likely why they have thrived in such a wide range of environments—from deep oceans to dry land,” she explained.
The implications of this research extend far beyond evolutionary history. Understanding molluscs is crucial not only for marine science but also for medicine, environmental studies, and even biotechnology. “This research provides a foundation for understanding one of the most successful animal groups on Earth,” said Prof. Dr. Julia Sigwart, Head of the Malacology Section at Senckenberg Research Institute. “By studying molluscs, we gain insight into how life adapts, diversifies, and thrives over time.”
From the smallest sea slugs to the most complex cephalopods, molluscs continue to shape ecosystems, inspire scientific discovery, and fascinate the human imagination. Now, at last, their ancient origins are no longer a mystery.
Scaphopods, like Fustiaria rubescens, are unique marine molluscs with a tusk-shaped shell. They are part of the newly named group: Megalopodifera, or the “big foot molluscs.”
Solenogasters, like Neomenia megatrapezata, are unique molluscs with worm-like bodies. This species was one of the genomes newly sequenced and analysed as part of this study.
