An international team of experts has resolved long-standing questions about the evolutionary history of mollusks, one of the most diverse zoological groups on the planet. The study, published in Science, reconstructs the family tree of mollusks and provides a genome-based perspective on their evolutionary history.
Professor Juan Moles, 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 the study, which responds to scientific debates that have persisted for decades.
In this study, the team analyzed the genomes of 77 mollusk species that are representative of eight major groups from around the world today, including lesser-known forms such as deep-sea monoplacophorans and solenogastropods, wormlike mollusks that live at great depths.
From microscopic bivalves to giant squid, from common garden snails to hydrothermal spring snails covered in iron scales, mollusks are organisms capable of thriving in a wide variety of habitats, including seabed, coastal, freshwater and terrestrial ecosystems.
Research now explains the extraordinary diversity in body shape, size, behavior, habitat and genome of mollusks, of which there are nearly 100,000 described species (and many yet to be discovered).
The mollusk tree of life: A new perspective
Despite their ecological and economic importance, the evolutionary relationships of mollusks have been difficult to decipher because of conflicting evidence from the study of fossils, their physical characteristics and their genetics.
The new genome-based phylogeny of the phylum Mollusca is consistent with the fossil record and morphology and confirms the ancestry 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,” says researcher Zeyuan Chen, first author of the paper and bioinformatician at the Senckenberg Research Institute and Natural History Museum Frankfurt (Germany).
“This ancestor probably had a hard shell, a foot for movement, no eyes and a radula, which is a specialized organ for feeding,” Chen continues.
Genomes reveal the ancestor of the garden snail
The study has confirmed that the evolutionary lineage of mollusks split early on into two major groups called Aculifera and Conchifera. Aculifera includes species with small needle-like spicules—and in some cases, shells—while Conchifera includes the groups of mollusks considered traditional, such as snails, clams and cephalopods.
The findings have also resolved a classic debate about the evolutionary relationships of some mollusks. Thus, the controversial living fossils or monoplacophorans (primitive mollusks that were considered extinct, headless and with a hooded shell) become the oldest branch within the Conchifera, followed by the cephalopods (squids, cuttlefish and octopuses).
The rest of the Conchifera form a group now known as the Megalopodifera—big-food bearing—which includes the enigmatic scaphopods (or tusk shells) along with clams, snails and slugs.
“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,” adds Zeyuan Chen.
“The new study provides a basis for understanding the evolution and biology of one of the most evolutionarily successful groups of animals on Earth,” says Professor Juan Moles, from the UB’s Department of Evolutionary Biology, Ecology and Environmental Sciences. “Understanding mollusks helps us to start answering big questions to understand how life adapts and diversifies over time.”
Beyond evolutionary knowledge, the findings open the door to applications in biotechnology and conservation, with an outstanding projection in areas ranging from environmental sciences to biomedicine, as some species are models for the study of human health and disease.
Looking ahead, the research team hopes to extend the study with the analysis of more species to explore how genetic diversity has driven innovation in the phylum Mollusca.
More information:
Zeyuan Chen et al, A genome-based phylogeny for Mollusca is concordant with fossils and morphology, Science (2025). DOI: 10.1126/science.ads0215
Provided by
University of Barcelona
Citation:
Mollusk family tree helps resolve long-standing evolutionary questions (2025, February 28)
