Historic Sea Spider Collection Unravelled: Loman’s Pycnogonid Legacy Revisited

More than a century after his death, the work of a Dutch schoolteacher who quietly became one of the most important figures in sea spider taxonomy is finally being mapped in full. Jan Cornelis Christiaan Loman (1856–1929), a biology teacher at the Amsterdam Gymnasium, described dozens of pycnogonid species while holding down a day job, and his specimens now form a cornerstone of the sea spider collection at the Naturalis Biodiversity Center (NBC) in Leiden. A new systematic review published in Zoosystematics and Evolution has catalogued his entire published output, tracked down his type specimens across institutions worldwide, and produced a checklist that researchers hope will prevent further loss of historically significant material.

Sea spiders, or pycnogonids, are marine arthropods whose unusual body plan has fascinated zoologists since the earliest days of natural history collecting. Natural history collections hold hundreds of millions of specimens gathered over roughly 270 years of biodiversity research, and they remain the keystone of taxonomy, a major source of material for phylogenomics and anatomy, and a massive data resource for ecology. Yet many collections are effectively inaccessible because their contents are poorly documented, and older material for which provenance is hard to trace risks being temporarily or permanently lost. Systematic inventory and digitisation are therefore paramount for preserving these materials and for keeping dependent research repeatable.

Naturalis hosts one of the most important pycnogonid collections in the world. Part of it, including the material of Paulus Peronius Cato Hoek (1851–1914), was deposited directly at what was then the Rijksmuseum voor Natuurlijke Historie. Other material arrived later from the Zoological Museum of Amsterdam, including the collections of Loman and of Jan Hendrik Stock (1931–1997). Together, Hoek, Loman and Stock described more than 300 sea spider species, roughly twenty percent of all known pycnogonid diversity, and much of that material is now curated in Leiden.

Loman himself remains a shadowy figure. Little is known about him beyond his teaching post, his donations to the ZMA collection, and the fact that he studied not only pycnogonids but also flatworms, harvestmen and tardigrades. He had a close connection with Heinrich Carl Redeke, who later became an authority on freshwater ecology, and through Redeke some of his collections were donated to the ZMA in 1933. Despite the biographical obscurity, his taxonomic contribution is anything but minor: he authored 24 publications on sea spiders, describing 54 species and six genera, of which 48 species and three genera are still regarded as valid today.

The material Loman studied came from an extraordinary range of sources and regions. He worked on specimens from southern Africa, the Antarctic Peninsula, Arctic seas, Southeast Asia, the Atlantic, Australia, the China Sea, Japan and the Mediterranean. He participated in the taxonomic study of samples from the Dutch Siboga Expedition of 1899–1900, which sampled between the southern Philippines, New Guinea, Timor, Java and Borneo; from the expeditions of Prince Albert I of Monaco; and from the Swedish Antarctic Expeditions of 1901–1903. His 1908 paper on Siboga material alone treated 29 new species, four new genera and one new subgenus.

The new review compiled a list of every species Loman described, complete with type localities, sampling depths and geographic coordinates drawn from his publications. The authors then matched published descriptions against the physical specimens in Leiden, where Loman’s material is stored in 70 percent ethanol, often accompanied by original handwritten labels and post-stamp-sized glass slide labels that record type localities and frequently note that the material belongs to a type series. All slides were scanned and made digitally accessible on the Bioportal platform.

The results are striking. The team recovered a total of 162 records at NBC corresponding to material described in Loman’s publications, 133 of which represent type material, including 19 holotypes and 37 syntypes. An additional 69 type parts preserved as microscope slides were also identified. Type material, or parts of it, was located for 42 species in total. Thirteen records among Loman’s non-type material were later reidentified as new species by subsequent researchers, and nine specimens were designated as type material by Stock in later decades, including the types of Rhopalorhynchus lomani, Rhopalorhynchus sibogae and Endeis biseriata.

Identifying historical type material is rarely straightforward. Under the International Code of Zoological Nomenclature, only material unambiguously extracted from type specimens can itself be considered part of the type series, yet historical material is often not physically labelled as such. The researchers therefore applied three criteria: the specimen had to be labelled as a new species in handwriting clearly attributable to Loman; the composition of the material had to be coherent with the original description, including specimen numbers and identified sexes; and it had to be traceable to the type locality or one of the original sampling stations. This approach proved especially valuable for glass slides, which frequently bore only cryptic notations such as “Japan” and “n. sp.” but could be linked to type series through locality data and old registration numbers.

The checklist also documents material that could not be found. Syntypes of Achelia superba from Sagami Bay, the types of Tanystylum oedinotum from the Falkland Islands, and various lots from the Swedish expeditions remain unlocated, while some specimens from South and West African material held in Gothenburg appear to have been lost, with empty jars found in their place. Recording these gaps is itself scientifically useful: it tells future researchers exactly what is missing, what to look for in other institutions, and what may have been dispersed or reidentified under different names over the past century.

Beyond its archival value, the work underscores how much biodiversity knowledge rests on the careful curation of specimens collected on expeditions more than a century ago. Loman’s name is honoured in two pycnogonid species, Nymphon lomani and Rhopalorhynchus lomani, and his descriptions remain the taxonomic anchor for dozens of valid species from the Indo-Pacific, the Southern Ocean and the Atlantic. By making his entire corpus traceable, specimen by specimen and slide by slide, the new checklist turns a scattered historical legacy into a usable research infrastructure, ensuring that the sea spiders he described remain accessible, verifiable and citable for the next generation of taxonomists.

Subject of Research: Systematic checklist of historic pycnogonid type material described by J. C. C. Loman

Article Title: Collections unravelled: Loman’s Pycnogonids

Article References: Bakker, P. A. J., & Sabroux, R. (2026). Collections unravelled: Loman’s Pycnogonids. Zoosystematics and Evolution, 102(1), 199-216. https://doi.org/10.3897/zse.102.174505

Image Credits: AI Generated

DOI: 10.3897/zse.102.174505

Keywords: pycnogonida, sea spiders, taxonomy, natural history collections, type specimens, Jan C. C. Loman, Naturalis Biodiversity Center, Siboga Expedition, zoological nomenclature, biodiversity digitisation, marine arthropods, collection management