The study, conducted by Bernhard L. Bock of the Institute for Zoology and Evolutionary Research at Friedrich Schiller University Jena, centers on Atolla wyvillei, a scarlet, bioluminescent deep-sea medusa first described by Haeckel in 1880 and named in honor of Sir Charles Wyville Thomson, the chief scientist of the Challenger expedition. Housed at the Phyletisches Museum Jena, the surviving type specimen has now been reexamined and documented with high-resolution imaging for the first time. More remarkably, the research reveals a previously unknown series of 29 microscope slide sections of a second syntype, discovered in the holdings of the Ernst-Haeckel-Haus in Jena, that directly connects Haeckel’s published plates to laboratory work performed on the original specimens.

The story begins with the Challenger expedition itself, the first scientific voyage to explore the deep sea on a global scale. Between 1872 and 1876, a crew of nearly 250 sailors, engineers, and officers, accompanied by a small scientific team, visited more than 500 stations across nearly 80,000 miles of ocean. They measured depths and temperatures, collected water samples, and dredged the seafloor, ultimately gathering more than 100,000 samples and specimens. The expedition permanently disproved Edward Forbes’s azoic hypothesis, which had held that no life could exist below 300 fathoms, and revealed an immense diversity of deep-sea organisms. It also discovered the Mariana Trench and the Challenger Deep, the deepest known point of the seabed, and even compiled the world’s oldest collection of micrometeorites using magnets to sample dredged sediments.

The expedition’s scientific output was staggering: a 50-volume report totaling nearly 30,000 pages, published between 1885 and 1895 by more than 75 contributing authors, describing around 4,700 new species. A set of these samples was sent to Jena, where Haeckel, already a leading authority in marine zoology, produced extensive illustrated monographs on radiolarians and deep-sea medusae. In total, Haeckel contributed 2,790 pages and 230 plates, nearly 10 percent of the entire publication. His plates, drawn largely with the camera lucida by himself and his lithographer Adolf Giltsch, remain among the most recognizable images of the entire expedition, and many were later adapted for his famous Kunstformen der Natur, a work that influenced artists from Kandinsky to Klimt and Munch.

Yet Haeckel’s methods attracted fierce criticism during his lifetime and afterward. Detractors argued that he fabricated non-existent taxa, lost primary type material, or produced illustrations useless for science. Much of the controversy has focused on his embryological drawings, but the charges bled into assessments of his entire body of work. The new study addresses these critiques head-on by physically reevaluating the type material of A. wyvillei. The surviving syntype, preserved in 70 percent ethanol, has shrunk to 40 millimeters in diameter, a reduction of 20 to 41 percent from the measurements Haeckel recorded for the Station 157 specimens, leaving it structurally resembling, as the author notes, a potato chip. Shrinkage artifacts are visible in the tentacles, lobes, umbrella, and gonads.

The decisive discovery came in 2025, when a small box containing microscope slide sections labeled in Haeckel’s handwriting as Atolla Wyvillei Discomedusae was found in the Ernst-Haeckel-Haus. The 29 slides, embedded in Canada balsam and bearing handwritten annotations describing each anatomical cut, were in poor condition, with cracked mounting medium, loose coverslips, and fragmented specimens. After careful restoration, the slides were examined and matched against Haeckel’s published descriptions. The orientations he noted for Plate 29 of the Challenger report, including radial, horizontal, and tangential sections, correspond precisely with the inscriptions on the slide cardboard, confirming that these slides represent at least one of the original individuals Haeckel examined and cementing their status as part of the syntype series.

This physical evidence demonstrates that several of Haeckel’s published observations could only have been made under a microscope, using histological sections to view the ovaries, distinct tissue layers such as epidermis, mesoglea, and muscle fibers, and the tiny sensory structures called rhopalia. Haeckel credited his preparator Reinhold Teuscher with making the sections, and his own remarks reveal the difficulty of the work: he succeeded only with considerable trouble in determining the rhopalia’s existence, and their anatomical nature could not be resolved because of their small size and the poor preservation of the umbrella margin. The number of rhopalar pedalia in the preserved type, 22, matches what the slides would be expected to show, though the historical cuts failed to intersect the sense clubs precisely.

The study also situates Haeckel’s illustrations within the broader visual culture of nineteenth-century marine biology. Comparing his plates with those of contemporaries such as Alfred Goldsborough Mayer, whose Medusae of the World relied heavily on simplified line drawings that highlighted only key diagnostic features, reveals a fundamental methodological difference. Haeckel’s plates overflow with detail and lettering, choreographed almost like a Baroque high altar, in a tradition of scientific realism aimed at enabling systematic comparison of sets of objects. His compositions move logically from whole-specimen overviews to cutaway views and magnified anatomical details, using stippling and hatching to convey three-dimensional structure. Drawing, the study argues, is fundamentally an exercise in abstraction, and Haeckel’s approach fully conformed to the scientific standards of his era, at a time when photography was expensive, logistically difficult for gelatinous specimens, and not yet widespread in natural science.

The author acknowledges the limits of the reevaluation. More than 150 years of storage have degraded the material, only one complete specimen of the former type-series survives, precluding new histological preparations, and the precise details of Haeckel’s preparation workflow remain unrecorded. The exact influence of Giltsch on the final plates also remains unquantified. Cautious extrapolation is therefore required when evaluating Haeckel’s broader output, and the study does not erase the legitimate debates surrounding his embryological figures. But for A. wyvillei, the verdict is clear: the species can be readily identified and distinguished from other members of the genus based on Haeckel’s work, and his illustrations were grounded in real morphological and histological examination rather than invention.

The broader implications reach into modern biodiversity science. The Challenger samples remain an indispensable historical collection, and historical baseline data from the expedition are now critical to understanding how modern ocean acidification is affecting marine ecosystems. The discovery underscores the hidden value of smaller institutional archives such as the Phyletisches Museum Jena, whose unexamined holdings may contain further unrecognized type specimens. An illustrated catalogue of the museum’s type collection is planned to give researchers broader access. As the study concludes, identifying and systematically reevaluating missing type material can resolve persistent systematic questions and recover invaluable cultural assets, ensuring that the legacy of the Challenger expedition, and of the controversial genius who illustrated it, continues to inform ocean science today.

Subject of Research: Historical reexamination of Ernst Haeckel's type specimens and illustrations of the deep-sea jellyfish Atolla wyvillei from the HMS Challenger expedition

Article Title: Portrayal of the deep sea: Haeckel’s Atolla wyvillei, the challenger expedition, and the boundaries of science and illustration

Article References: Bock, B. L. (2026). Portrayal of the deep sea: Haeckel’s Atolla wyvillei, the challenger expedition, and the boundaries of science and illustration. The Science of Nature, 113(5), Article 109. https://doi.org/10.1007/s00114-026-02154-8

Image Credits: AI Generated

DOI: 10.1007/s00114-026-02154-8

Keywords: Ernst Haeckel, Atolla wyvillei, HMS Challenger expedition, deep-sea jellyfish, scientific illustration, type specimens, histology, marine biology, history of science, taxonomia, museum collections, Coronatae

The retraction centers on problems with the paper’s microscopy images, which formed the visual backbone of its toxicity evaluation. According to the notice, concerns were raised after publication regarding image overlap in Figure 7f between the Control and Unloaded hydrogel groups. In practical terms, this means that two images that were supposed to show different experimental conditions—one representing untreated control tissue and the other tissue exposed to the hydrogel formulation without drug—appeared to contain the same or substantially identical pictorial content. For readers assessing whether a biomaterial is safe, such duplication is not a cosmetic flaw. It undermines the very comparison that the toxicity section was designed to establish, because the reader cannot know what the true untreated baseline looked like or whether the loaded and unloaded formulations produced distinct histological effects.

The problems did not stop within the retracted paper itself. The Editors-in-Chief also found that the Figure 7c Control image appeared to overlap with an image labeled Figure 11 Lung I in an earlier article by overlapping authors, published in Advanced Polymer Technology in 2018 under the title “A hydrophobic–hydrophilic cross-linked matrices for controlled release formulation of highly water-soluble drug venlafaxine: synthesis and evaluation studies.” That earlier work described a different drug delivery system for a different active compound, venlafaxine, yet apparently shared histological imagery with the salbutamol hydrogel study. When the same micrograph appears in papers describing distinct experiments on distinct drugs, at least one use of the image cannot be an honest record of the experiment it is presented alongside, a situation that strikes at the foundation of experimental reporting.

Adding to the pattern, the retraction notice reports that a number of other images in Figure 7 of the Polymer Bulletin paper appear highly similar to those in Figure 12 of a second earlier publication, a 2020 paper in AAPS PharmSciTech describing poloxamer-407 co-poly(2-acrylamido-2-methylpropane sulfonic acid) cross-linked nanogels for solubility enhancement of the antipsychotic drug olanzapine. Notably, that nanogel paper has itself already been retracted, a fact flagged in the retraction notice’s reference list. Taken together, the overlaps span at least three publications and multiple drug delivery platforms, suggesting that the same or near-identical toxicity images circulated across a family of related manuscripts rather than being generated fresh for each experiment.

For readers unfamiliar with how biomedical materials research is documented, the significance of histological figures deserves emphasis. In hydrogel toxicity studies, researchers typically implant or administer the material, harvest organs such as liver, kidney, heart, and lung, section the tissue, stain it—commonly with hematoxylin and eosin—and photograph it under a microscope. These images are the primary evidence that a formulation does not cause inflammation, necrosis, or other tissue damage. Because each experimental group generates its own set of slides, every image should be unique to its condition, animal, and time point. Image duplication between a control group and a treated group, or between entirely separate studies, therefore cannot be explained by ordinary technical variation. Modern forensic image analysis, which detects duplicated regions, spliced panels, and reused micrographs across journals, has made such duplications increasingly easy to detect and increasingly difficult for journals to ignore.

The retracted study itself had described an appealing materials-science concept. Gelatin, a biodegradable protein derived from collagen, is attractive for drug delivery because it is biocompatible, inexpensive, and can be chemically cross-linked to form hydrogels that swell in aqueous environments. A swellable hydrogel matrix can, in principle, control the release of a highly water-soluble drug such as salbutamol sulphate by regulating how quickly water penetrates the network and how the polymer chains relax, allowing the drug to diffuse out over an extended period rather than immediately. The paper reported characterization of these networks alongside toxicity evaluation intended to demonstrate biological safety. None of the retraction documentation disputes the underlying chemistry concept; what has been invalidated is the evidentiary record supporting the paper’s claims, particularly the safety data.

The human dimension of the case is also documented in the notice. Syed Faisal Badshah, one of the co-authors, does not agree to the retraction. The remaining authors—Naila Rafique, Mahmood Ahmad, Muhammad Usman Minhas, Nadia Shamshad Malik, and Kifayat Ullah Khan, affiliated with The Islamia University of Bahawalpur, the University of Sargodha, and Capital University of Science and Technology in Pakistan—have not responded to any correspondence from the editor or publisher about the retraction. Under Committee on Publication Ethics guidance, which Springer Nature journals follow, a retraction does not require unanimous author consent when the evidence of misconduct or unreliability is sufficiently strong; the journal’s editorial leadership can act unilaterally to protect the literature. The notice’s account of non-response and disagreement is a familiar profile in cases built on image integrity findings.

Retractions of this kind carry consequences well beyond the individual paper. Clinicians and formulation scientists who encounter the work may have incorporated its toxicity conclusions into reviews, meta-analyses, or the design of follow-up hydrogel systems for salbutamol, a drug used daily by millions of people with asthma and chronic obstructive pulmonary disease. Although a retracted paper’s claims about gelatin hydrogels are unlikely to have influenced approved clinical practice, the case illustrates why controlled-release research depends on trustworthy preclinical safety data. It also highlights the value of the linked-paper problem: when images recur across a group of manuscripts from the same laboratory, each retraction weakens confidence in the others, and editors increasingly treat such clusters as grounds for systematic review rather than case-by-case dismissal.

For the broader polymer and pharmaceutical sciences community, the episode is a reminder that characterization data—swelling ratios, drug release kinetics, and mechanical testing—are only as credible as the biological and imaging evidence that accompanies them. Journals now routinely screen submissions with image-integrity software, and readers can verify the retraction status of the article through the CrossMark badge on the publisher’s page and the linked retraction notice. The retracted article remains accessible online but is watermarked as retracted, and the notice directs readers to the original publication record. The scientific question the paper posed—whether gelatin-based swellable hydrogels can safely and effectively control the delivery of salbutamol sulphate—remains legitimate and open, but any future answer will need to rest on images and data that can withstand the scrutiny this study ultimately could not.

Subject of Research: Retraction of a study on gelatin-based swellable hydrogels for controlled delivery of salbutamol sulphate due to image overlap concerns

Article Title: Retraction Note: Designing gelatin-based swellable hydrogels system for controlled delivery of salbutamol sulphate: characterization and toxicity evaluation

Article References: Retraction Note: Designing gelatin-based swellable hydrogels system for controlled delivery of salbutamol sulphate: characterization and toxicity evaluation. (n.d.). https://doi.org/10.1007/s00289-026-06682-1

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06682-1

Keywords: retraction, gelatin hydrogels, salbutamol sulphate, controlled drug delivery, Polymer Bulletin, image duplication, toxicity evaluation, research integrity, swellable hydrogels, Springer Nature, histology, pharmaceutics