In the cool, plankton-rich waters of the North Atlantic, a microscopic drama unfolds that may finally unravel one of biology’s most enduring mysteries: how a simple, hollow tube transforms into a fully functional, three-dimensional organ. Biologists have grappled for decades with the question of organ morphogenesis, the process by which organs acquire their characteristic shapes, because the earliest stages of development are often hidden deep within opaque tissues. Now, a team led by developmental biologist Margherita Perillo at the Marine Biological Laboratory (MBL) in Woods Hole has turned to an unlikely hero—the larval sea star—offering a transparent window into the deepest principles of organ formation. Their work, published in Discover Developmental Biology, introduces a newly defined structure called the hydro-vascular organ (HVO), a fluid-filled tubular loop that serves as the precursor to the adult sea star’s internal anatomy, and demonstrates that by comparing its development across multiple species, we can extract universal rules about how life builds complexity from simplicity.
The HVO begins as an almost comically unassuming structure: a tiny, blind-ended tube that arises from the left side of the larval body, floating in the spacious blastocoel like a loose thread. Yet this thread is far from passive. Over the course of mere days, it elongates, bifurcates, and undergoes a series of precisely choreographed movements that fuse separate branches into a continuous, looping circuit. To appreciate why this matters, one must recall that the human heart originates as a linear heart tube that folds and septates, our lungs emerge from a single foregut diverticulum that undergoes rampant branching morphogenesis, and our kidneys arise from the ureteric bud, which also begins as a simple epithelial tube before arborizing into millions of nephrons. Perillo’s central insight is that the sea star HVO recapitulates this same fundamental motif—tubulogenesis followed by patterned branching and fusion—but does so in an embryo that is optically clear, genetically tractable, and accessible in vast numbers. This confluence of traits transforms the HVO into a powerful comparative model, one that might accelerate the discovery of the molecular and mechanical signals that ensure a tube becomes a heart in one species and a water vascular system in another.
Margherita Perillo and her colleagues focused their comparative analysis on three species of sea star: Asterias forbesi, the common Forbes sea star found along the eastern seaboard of the United States; Patiria miniata, the bat sea star with its distinctive webbed arms; and Astropecten californicus, the red comb sea star that plows through sandy bottoms in the Pacific. Each species forms an HVO during metamorphosis, yet the developmental choreography is subtly but significantly different. In Asterias forbesi, the first visible rudiment of the HVO sends paired tubular projections anteriorly toward the developing stomach, which then curve ventrally and ultimately fuse across the oral midline, creating a complete ring-like circuit. In the bat sea star, by contrast, the initial tubular connection forms posteriorly before any significant elongation toward the stomach occurs, establishing an early anchor point that changes the geometry of subsequent growth. The red comb sea star takes yet another route, merging its tubes near the intestinal rudiment first, then expanding the circuit outward in a radial pattern that foreshadows the pentaradial symmetry of the adult. These divergent strategies, Perillo explains, are akin to different architectural plans that all arrive at the same blueprint for a house: the final HVO anatomy is remarkably conserved across the three species, suggesting that evolutionary pressures have arrived at multiple developmental solutions for the same endpoint.
To visualize these delicate processes, Perillo’s team employed a combination of brightfield time-lapse microscopy, confocal imaging with fluorescent actin and nuclear markers, and three-dimensional reconstructions from optical sections. Because sea star larvae are completely transparent—a property resulting from their minuscule size, lack of pigmentation, and the optical clarity of the surrounding seawater—the researchers could track individual cells as they migrated, divided, and changed shape within the elongating HVO walls. They observed that the tube is not simply inflating like a passive balloon; rather, its epithelial cells undergo concerted apical constriction, intercalation, and oriented cell division, processes collectively known as convergent extension, which drive tubular elongation in vertebrates as well. This discovery places the HVO directly within the mainstream of developmental biology’s current understanding of tube morphogenesis, linking a spineless marine larva to the embryos of mice, chickens, and humans. The team also detected localized pockets of phosphorylated myosin light chain, a molecular signature of actomyosin contractility, concentrated at the tips of advancing tubular branches, implying that the tubes are pulled forward by supracellular contractile cables, not merely pushed by fluid pressure.
One of the most technically exquisite aspects of the research was the team’s ability to perform live imaging for up to 72 continuous hours without perturbing normal development. This required the design of custom microfluidic chambers that maintained seawater flow, oxygen levels, and temperature while immobilizing the larvae just enough to capture sub-micron resolution. The resulting movies, some of which accompany the publication, reveal the HVO’s growth as a dynamic process punctuated by periods of rapid extension and intermittent pauses during which the tubular walls remodel. In Asterias forbesi, for instance, the anterior-growing tubes stall precisely when they contact the stomach, a pause that coincides with a local increase in the expression of E-cadherin, a cell adhesion molecule known to mediate tissue-tissue interactions. This suggests a mechanical feedback loop: the growing tip senses the resistance of the target organ, which triggers adhesive strengthening, which in turn stabilizes the new connection before fusion occurs. Such mechanosensitive checkpoints are suspected to operate during mammalian heart looping and lung branching but are notoriously difficult to study in utero; the sea star HVO may provide a quantitative platform to dissect them.
The evolutionary context adds a rich layer of significance. Echinoderms, the phylum that includes sea stars, sea urchins, and sea cucumbers, are among the closest invertebrate relatives to chordates, the group that encompasses vertebrates. This phylogenetic position makes them an ideal outgroup for inferring ancestral developmental mechanisms that may have been present in the last common ancestor of deuterostomes, the superphylum that gave rise to both echinoderms and humans. Perillo’s findings hint that the last common ancestor of all deuterostomes likely possessed a simple tube-based organogenetic program that could be co-opted into different adult structures—a hydro-vascular system in echinoderms, a circulatory system in vertebrates, a respiratory system in hemichordates. By comparing the gene regulatory networks that control HVO formation in sea stars with those that govern heart, lung, and kidney development in vertebrates, the MBL team and others in the field can begin to reconstruct the ancient genetic toolkit that first allowed tubes to become organs. Already, preliminary data from RNA sequencing of microdissected HVO tissues indicate the expression of homologs of key vertebrate tubulogenesis genes such as Fgf10, Shh, and Bmp4, a molecular echo that resounds across half a billion years of evolution.
Beyond the evolutionary revelations, Perillo’s research has tangible implications for human medicine. Many diseases that afflict human organs are, at their core, disorders of tubular architecture. Polycystic kidney disease, for example, results from defective mechanosensation in renal tubules, causing them to balloon into fluid-filled cysts and eventually eliminate kidney function. Fibrosis, the pathological accumulation of scar tissue that stiffens the heart, lungs, and liver, often begins with aberrant signaling from damaged epithelial tubes. Even congenital heart defects, the most common birth anomalies in humans, frequently stem from errors in tube fusion or looping. The sea star HVO, with its robust regenerative capacity—adult sea stars can regrow entire arms and their internal organs—offers a natural model to study not only how tubes form correctly, but also how they might be encouraged to repair themselves after injury. Perillo’s lab has already begun exploring whether the molecular signals that seal fusing HVO branches can be reactivated to promote healing in damaged mammalian epithelia, opening a provocative line of translational inquiry.
The laboratory’s next phase of investigation will drill deeper into the question of how the HVO maintains its orientation and prevents fibrosis even as it undergoes constant remodeling during metamorphosis. Metamorphosis is a time of profound upheaval for the larval body; tissues that were essential for planktonic life are dismantled, and the adult body plan is assembled from scattered progenitor cell populations. Throughout this chaos, the HVO must preserve its tubular integrity, directing the formation of the adult water vascular system that powers the sea star’s iconic hydraulic tube feet. Perillo hypothesizes that the organ’s resistance to fibrosis may involve the continuous expression of matrix metalloproteinases, enzymes that degrade collagen and prevent excessive scarring, alongside a population of resident macrophages that patrol the basement membrane and remove cellular debris. If this hypothesis holds, the sea star could provide a masterclass in how to keep a dynamic organ supple and functional, with direct takeaways for designing antifibrotic therapies.
The broader scientific community has greeted these findings with considerable excitement, in part because they arrive at a moment when developmental biology is increasingly turning toward “accessible model systems” that can complement traditional work in mice, zebrafish, and fruit flies. Sea star larvae can be cultured in large numbers at low cost, their genomes have been sequenced, and they are amenable to CRISPR-mediated gene editing, all features that democratize research and allow for high-throughput functional screens. The MBL, where Perillo conducted this work, has a storied history of embracing marine organisms as biological models—from squid giant axons that taught us how nerves fire, to horseshoe crab blood that detects bacterial endotoxins—and the HVO story is the latest chapter in that tradition. The institution’s summer embryology courses, which attract researchers from around the globe, have already begun incorporating sea star larvae into practical modules, ensuring that the next generation of scientists will see the HVO as a standard model alongside the chick embryo and the Xenopus tadpole.
The publication date of the study, June 16, 2026, marks not an endpoint but a beginning. Perillo’s paper in Discover Developmental Biology, titled “Comparative analysis of Asterias forbesi development reveals distinct mechanisms of hydro-vascular organ formation across sea stars,” meticulously catalogues the developmental sequences in all three species and provides the first standardized staging scheme for the HVO. This staging scheme, complete with high-resolution reference images and molecular markers, will serve as a Rosetta Stone for future researchers who wish to manipulate the system pharmacologically or genetically. Already, collaborators at other institutions are planning experiments to perturb specific signaling pathways and observe the consequences on HVO branching, aiming to build a formal mathematical model of the branching algorithm. Such a model could predict, for example, how the architecture of a developing organ changes when the rate of cell division in one branch is altered, a scenario that mimics the stochastic nature of congenital malformations.
As the story of the HVO diffuses through journals and press releases, the charismatic image of the translucent larval sea star with its glowing, looping tube is capturing the public imagination. The photographs by Margherita Perillo, showing the egg cells and early embryonic stages of Asterias forbesi in brightfield magnificence, underscore the sheer aesthetic beauty of scientific discovery. In these images, the unfurling HVO resembles a delicate calligraphic stroke against a field of scattered cells, a visual metaphor for the emergence of order from chaos. It is a reminder that the most profound answers about human existence—how our organs form, how they fail, and how we might mend them—can sometimes be found by looking through glass-clear water at a creature most people would pass without a second glance. The sea star has been teaching us lessons about regeneration and body plan for over a century; now its larva is poised to illuminate the universal language of tubes, one frame of a time-lapse movie at a time.
Perillo’s team envisions a future in which the HVO becomes a platform for drug screening, where small molecules are tested for their ability to correct tube fusion defects or prevent fibrosis, not in costly mammalian models but in the transparent embryos of sea stars. Because the HVO forms within days and can be imaged without perturbing the organism, thousands of compounds could be assayed simultaneously in microtiter plates, with automated microscopy detecting subtle changes in tube length, branch angle, or fusion efficiency. Such a screen could identify lead compounds for kidney or lung fibrosis that would then be validated in mammalian systems, accelerating the notoriously slow pipeline from discovery to therapy. It is a vision that marries fundamental curiosity with translational ambition, the hallmark of the MBL’s century-spanning ethos.
Reflecting on the work, Perillo herself emphasizes the collaborative nature of the endeavor, crediting the MBL’s unique environment where experts in evolution, cell biology, and computational imaging mingle daily, often over coffee in the historic mess hall. The hydro-vascular organ, she insists, is not just a structure in a sea star, but a conceptual bridge connecting distantly related phyla through shared developmental logic. As her team publishes the foundational comparative atlas, invitations pour in from conferences and university departments eager to hear how a creature that arm-wrestles clams can teach us about our own inner architecture. The answer, it turns out, flows through a tiny transparent tube that loops and branches with a purpose we are only just beginning to understand, and each new observation promises not just a fact about sea stars, but a deeper principle about what it means to be a bilaterian animal, building complexity from a single humble tube.
Subject of Research: Animals
Article Title: Comparative analysis of Asterias forbesi development reveals distinct mechanisms of hydro-vascular organ formation across sea stars
News Publication Date: 16-Jun-2026
Web References: https://link.springer.com/article/10.1007/s00427-026-00731-5
References: Perillo, M., et al. (2026). Comparative analysis of Asterias forbesi development reveals distinct mechanisms of hydro-vascular organ formation across sea stars. Discover Developmental Biology, DOI: 10.1007/s00427-026-00731-5
Image Credits: Image credit: Margherita Perillo
Keywords: Developmental biology, organ morphogenesis, sea star, hydro-vascular organ, tubulogenesis, echinoderm, marine model organism, branching morphogenesis, fibrosis, evolution of development, Marine Biological Laboratory
Tags: developmental biology discoveriesechinoderm larval anatomyfluid-filled tubular loop evolutionhydro-vascular organ precursorlarval sea star developmentMargherita Perillo researchMarine Biological Laboratory Woods Holeorgan formation principlessea star organ morphogenesisthree-dimensional organ shapingtransparent embryo modeltube morphogenesis mechanism
