The Department of Organismic & Evolutionary Biology at Harvard

Professors Mansi Srivastava and Carrie Albertin, curators of Invertebrate Zoology (Mansi) and Malacology (Carrie) in , joined MCZ staff and OEB students to visit the Woods Hole Oceanographic Institution .ocean 🌊
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🚢The group experienced a behind-the-scenes-tour of WHOI’s three research vessels: R/V Neil Armstrong, R/V Atlantis and HOV Alvin, one of the world’s fist deep-ocean submersible commissioned in 1964! The vessels are responsible for the collection of over 50,000 specimen lots cataloged in the MCZ collections and curated by OEB professors.
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The group were also treated to a tour of the Marine Biological Laboratory - - marine aquatic animal facility including squid larvae undergoing research in Carrie’s laboratory at MBL. 🦑

Photos by Jennifer Winifred Trimble and Mansi Srivastava

We are hiring! OEB seeks a Curriculum and Pedagogy Manager. Apply using the QR code in image, or visit the OEB website’s employment page today!

For every two vertebrates on Earth, one is a fish. Ray-finned fishes (like salmon, tuna, trout, goldfish) account for 95% of fishes and thrive everywhere from deep-sea trenches to Himalayan rivers. Yet we know almost nothing about their brains! Postdoc Rodrigo Figueroa wants to change that.

In a new study in PRSB, Rodrigo and Professor Stephanie Pierce CT-scanned 87 ray-finned fish species and found something wild: while mammal brains snugly fill their skulls, some fish brains occupy less than 5% of their skull space. The rest? Filled with fluid, blood vessels, and immune organs. Turns out fish aren’t simple — they’re just built completely differently than we assumed.

The team also found a link between brain size and water depth: deep-sea fishes — on the ocean floor or in open-water — tend towards smaller brains. But a tiny brain in a big head does have some advantages, for instance meningeal tissue surrounding the brain may act as a protective bumper for impact or variations in pressure.

The study discovered that as the fish matured, brain size relative to skull size varied wildly — from near-full occupancy in hatchlings to 20-30% in mature adults, or even extreme in certain fish lineages. In the coelacanth, a famous living fossil, the brain fills nearly the entire cavity in youth before shrinking to a staggering 4% in adulthood!

This study is rewriting the rulebook on brain evolution and reminding us that mammal brains are the weird exception, not the standard.

Rodrigo’s big question now: did diverse brain shapes drive fish’s global success, or did their environments shape their brains? With 87 down and 35,000 species left to scan, the adventure’s just beginning.

Images: An array of specimens used in the study (Rodrigo Figueroa); Shape variation and fit between the brain (pink) and endocast (beige) across extant ray-finned fishes plotted on an evolutionary tree. Branch colors represent Brain Endocast Coefficient. Tip circles represent endocast complexity. (Rodrigo Figueroa PRSB 2026).

Congratulations to Wendy Valencia Montoya (PhD ‘25, Naomi Pierce, Advisor) awarded The Theodosius Dobzhansky Prize. The Theodosius Dobzhansky Prize is awarded annually by the Society for the Study of Evolution to recognize the accomplishments and future promise of an outstanding early-career evolutionary biologist.

Wendy is honored for her research investigating the molecular basis of specialized species interactions, such as how signals and senses evolve to enable communication between organisms, as well as the molecular pathways that confer resistance in species that have adapted to feed on highly neurotoxic plants. Wendy’s work brings together evolutionary biology, sensory physiology, and comparative genomics to understand how organisms adapt to rapidly changing environments and how sensory innovations arise.

Wendy, currently a Junior Fellow in the Harvard Society of Fellows, will present the Dobzhansky Prize talk during the Evolution meeting in June.

For 270 million years, trilobites ruled the oceans — and we finally know how they breathed. A groundbreaking study led by postdoc Sarah Losso and co-author Javier Ortega-Hernandez, just confirmed that the feathery structures (filaments) on trilobite limbs were fully functioning gills. The study also settles a decades-long debate about how these animals breathed.
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Using advanced 3D modeling and comparisons to modern marine life, the team found that trilobite gill surface areas rival those of crustaceans alive today. One surprising finding: larger trilobites didn’t grow more filaments to breathe better – the grew longer ones to meet rising oxygen demands.
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Over 22,000 species, hundreds of millions of years of ocean dominance, and science is still uncovering their secrets. Ancient life just got a whole lot clearer.
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Image: Gil Morphology in Aquatic Arthropods - (a – f) Exopodites of Paleozoic trilobites with lamellae (lm). Surface area calculations support the interpretation of exopodites as gills (g, h) Micro-CT scan of gills of the modern Atlantic horseshoe crab. (I, j) Micro-CT scan of the modern Jonah Crab. Gills of modern arthropods have thousands of thin lamellae to increase surface area. Credit: Sarah R. Losso (BL 2026).

The FAS Current sat down with Andrew Knoll, Fisher Research Professor of Natural History and Earth and Planetary Sciences Emeritus, to discuss his new book “Earth and Life: A Four Billion Year Conversation” on the 4-billion-year “conversation” between Earth and life — and recent interruptions by humans.
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How did the world as we know it—from the soil beneath our feet to the air we breathe and the life that surrounds us—come to be? Geologists have proposed one set of answers while biologists have proposed another. Earth and Life is the first book to reveal why we need to listen to both voices—the physical and the biological—to understand how we and our planet became possible.
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Interview: https://tinyurl.com/4v8rd35s
Book: https://tinyurl.com/4vfffyn2
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Image of Andy in Newfoundland Canada, courtesy of Andy Knoll

Meet Megachelicerax cousteaui, a 500myo sea predator that just rewrote the evolutionary history of chelicerates -- the group that includes spiders, scorpions, horseshoe crabs, sea spiders.

The discovery, published in pushes the origin of this lineage back by 20 million years. Previously, the oldest known chelicerates dated to the Early Ordovician (480 million years ago). Research scientist Rudy Lerosey-Aubril discovered the fossil’s “shocking secret” after 50 hours of meticulous cleaning. He revealed a pair of pincer-like claws where antennae typically reside on Cambrian arthropods. “It took me a few minutes to realize the obvious,” Lerosey-Aubril noted. “I had just exposed the oldest chelicera ever found.” Chelicera (the claws) are what distinguish spiders from insects.

Megachelicerax proves that specialized body regions and chelicera evolved before head appendages lost their outer branches to become the legs we recognize on modern spiders. Co-author Prof. Javier Ortega-Hernández, Curator of Invertebrate Paleontology in , explains that this find “reconciles several competing hypotheses” regarding arthropod evolution, “in a way, everybody was right.”

The fossil was discovered by renowned avocational fossil collector, Lloyd Gunther, and donated to the Kansas University Biodiversity Institute and Natural History Museum in 1981 for further study before Lerosey-Aubril offered to investigate as part of his research on early arthropods. It is named in honor of French explorer Jacques-Yves Cousteau for his work raising awareness of the beauty and vulnerability of the undersea.

Today, chelicerates include more than 120,000 living species inhabiting both terrestrial and aquatic ecosystems and deeply influencing our lives from pop-culture to medical andagricultural contributions.

Images: modern spider next to the fossil (Lerosey-Aubril); artistic reconstruction of Megachelicerax approaching prey by Masato Hattori: the fossil showing it’s spectacular chelicera (Lerosey-Aubril)

A fascinating new study published in PNAS is changing how we look at the oyster. We’ve always known these bivalves are experts at regulating their internal chemistry to build their hard shells, but it turns out they aren’t doing it alone.

Postdoctoral Researcher, Andrea Unzueta Martinez, led a team from Professor Peter Girguis’s lab that discovered oysters actually outsource some of the heavy lifting to specialized microbes living in a secluded pocket of fluid between the oyster’s body and its shell. Using a specialized “catheter” Andrea devised to sample this fluid, they found that the microbes and the oyster were simultaneously activating genes at the same time. Most surprisingly, the microbes were expressing genes specifically designed to help precipitate calcium carbonate—the very building blocks of the oyster’s shell!

When these microbes get to work, the oyster activates its neuroimmune system. Rather than using this system to fight off an infection, the oyster appears to be “talking” to its microbial partners to coordinate shell production. This discovery is a game-changer for understanding ocean resilience. As our waters become more acidic due to climate change, it takes significantly more energy for marine life to maintain their skeletons. By sharing the workload with microbes, oysters might be using a clever survival strategy to save energy and thrive in shifting environments.

From oysters in a tide pool to humans and our own gut health, we are all living in—and relying on—a microbial world. Understanding these tiny conversations could be the key to predicting how marine life will adapt to the future of our oceans. 🌊🔬

Article link: https://tinyurl.com/4fswk73x Image: Andrea uses the special catheter, which provides a watertight port for one-way access to collect microbe-filled fluid from the oyster.

ClimateResilience

Amber Rock (PhD candidate in The Department of Organismic & Evolutionary Biology at Harvard) and her advisor Professor Mansi Srivastava (MCZ Curator in Invertebrate Zoology) were able to isolate and rearrange the cells of early stage embryos and found that the cells showed extraordinary flexibility – in some cases single cells grew into a full-grown worm. The research goes against previous assumptions that because individual cells at this stage have different roles, removing or rearranging them would prevent growth of a complete organism.

Research published in Current Biology. Read more at https://www.eurekalert.org/news-releases/1120623

image shows a developing three-banded panther worm embryo at zygote, 2-cell, 4-cell, and 6-cell stages). Scale bar 100 microns. By Amber Rock