Portrayal of the deep sea: Haeckel's Atolla wyvillei, the challenger expedition, and the boundaries of science and illustration.

The Challenger expedition marked a turning point for marine biology, revolutionizing the scientific research of ocean life. It yielded a report of 50 volumes totaling nearly 30,000 pages-a monumental result that remains unchallenged. Among its vast contributions are reports by Ernst Haeckel on previously unknown species of radiolarians and medusae, which stand out for their lasting influence on the taxonomy of marine organisms. Atolla wyvillei Haeckel, 1880 is among these newly described medusae, named in honor of Sir Charles Wyville Thomson, the chief scientist of the HMS Challenger. Housed in the holdings of the Phyletisches Museum Jena (PMJ), the type specimen of A. wyvillei is carefully reexamined and documented with high-resolution imaging here for the first time. Furthermore, previously unknown microscope slide sections of an additional syntype of A. wyvillei are revealed. By directly comparing these primary physical preparations with Haeckel's published plates, this study provides empirical evidence to resolve long-standing historical debates regarding Haeckel's reliance on artistic interpretation or fleeting species descriptions. This physical reevaluation demonstrates that his illustrations were grounded in meticulous histological analysis, thereby providing an objective basis to reassess Haeckel's taxonomic legacy and safeguard primary type material for contemporary and future research.