Ernst Haeckel and the Polycystina


Radiozoa is a taxonomic phylum containing the microscopic plankton commonly referred to as radiolarians. These are tiny organisms similar to diatoms in that they have a supporting structure made from biologically deposited opaline silica. But radiolarians radically differ from diatoms in that diatoms contain chlorophyll, a specialization enabling them to photosynthesize energy-providing compounds. This naturally associates them taxonomically with the plantlike plankton ecologically grouped as phytoplankton. In contrast, radiolarians never contain chlorophyll. Their growth and reproduction must be fueled by feeding upon previously created organic compounds. Such animal-like protozoans are included in the ecologically functional group zooplankton. The Polycystina is a smaller taxonomic class within the phylum Radiozoa. Antique slides may carry either name on their label. The polycystines are an exclusively marine group and contain the most beautiful radiolarian examples. The silica supporting structures of Polycystina can be lacelike, appear as needlelike radiating rays or both. Their glass skeletons are physically fragile but chemically extremely stable. Polycystina skeletons can remain unchanged in marine sediments for eons, provided they are not exposed to undue stress from compaction. Intact polycystine skeletons have been isolated from geological deposits as old as the Cambrian era.

       The intricacies of polycystine, cage-like, glass supporting structures are beautiful when viewed through a microscope while using dark-field illumination. When writing about microscopy, Victorians often referred to polycystines as either the “jewels” or “gems” of the sea. Richard Kerr in his 1905 book on photomicrography, said the following about them:

Whenever a number of these fossil forms are placed under the microscope, they will be found to be a thing of beauty and joy forever. It is no exaggeration to say that sermons have been preached which have been prompted by a microscopic view of these matchless and exquisitely beautiful organisms — part of Nature’s building material. (Kerr 1906)

The beauty of microscopic plankton, and particularly that of the polycystines, was brought to the attention of Victorians by the German artist and scientist Ernst Haeckel (1834–1919). He is best known for his 1906 book, Art Forms in Nature, a work that was issued late in his career and is still in print. Haeckel’s respected standing as an expert for the identification and classification of microscopic life began forty-four years earlier. His first radiolarian drawings were published in an 1862 monograph where he described the many new species he discovered after two years of study along the Grecian coastline. Because of the beautiful artistic workmanship displayed in this work, Haeckel was invited to investigate the marine sediments collected by the British oceanographic ship the HMS Challenger. The Challenger circumnavigated the earth’s oceans between the years 1873 and 1876. Among the many responsibilities carried out by the ship’s crew and scientists were sounding the ocean’s depths and collecting ocean bottom sediments from each sounding site. This glimpse into the sea’s great abyss generated great interest by Victorian microscopists. Commercial slide mounters who were able to obtain samples found slides made from them to be in popular demand from their catalog’s listings.

       Haeckel spent years microscopically examining thousands of vials of collected benthic sediments brought home by the Challenger. The task culminated with his publishing a multi-volume illustrated work describing over a thousand microscopic species found in the samples. The book, although expensive, was successful and widely distributed. It was purchased primarily by university libraries and scientific societies that maintained collections for use by their membership. In particular, Haeckel’s artistic talents brought the beauty of polycystines to wide public attention and inspired artistic adaptation of their design.

       Haeckel’s polycystine drawings inspired the French architect René Binet (1866–1911). Binet was asked to design an edifice for the entranceway to the Paris Exposition of 1900. What he created strongly follows the lines of a polycystine found within the genus Nassellaria. The structure, named La Porte Monumental, was erected on the grounds at La Place de la Concorde, where it famously served as the exposition’s portal of entry.

LA PORTAL MONUMENTALE, Exposition Internationale de 1900 (The entranceway to the Paris International Exposition of 1900) (A photographic postcard measuring 3.5 x 5.5 inches)

Several Victorian commercial slide mounters obtained benthic samples from the Challenger expedition. They cleaned the sediments and made slides labeled with both the Challenger’s navigational coordinates and the depth from which the specimens were collected (see p xx). Microscope slides made from Challenger materials were popular with amateur microscopists. The slides gave their purchasers the opportunity to search through sediments taken from the ocean’s great depths and provided the thrilling chance of coming across a never-before-seen species. The Challenger’s ship log had been published, so the collection date for the samples on a slide was findable by looking up the navigational coordinates. The location could also be pinpointed on a world globe fueling their mystique.

Polycystines shed their glass cages when they reproduce, are stressed and when they die. The most abundant source of polycystine skeletal remains turns out not to be the ocean seabed, but sedimentary geological strata where they have accumulated over eons. In 1846, Dr. John Davy (1790–1868) discovered a trove of Polycystina in a sedimentary layer on the Caribbean island of Barbados. John Davy, the brother of the well-known scientist Sir Humphry Davy (1778–1829), was awarded the rank of Inspector General for Hospitals following the battle of Waterloo while serving in the Royal Army Medical Corps. During the late 1840s, Davy was assigned to Barbados. At the time he stated: “I believe to have the only microscope on the islands.” While investigating the natural history of Barbados, Davy found a layer of chalky claylike material abounding with the skeletal remains of polycystines. He read both the location and how he discovered the radiolarian remains into the minutes of the July 1849 meeting of the Barbados Agricultural Society. Doing so created a permanent record attributing the Barbados discovery to himself. Davy returned to England with a quantity of the sedimentary material that he shared with a few of his microscopist friends. Various amounts were sold to others for study or resale.

Beautiful slides of polycystines can be made from Davy’s sediments, but the chalky material must first be treated with powerful acids to dissolve and remove obscuring carbonate material. This comes mostly from mollusk shells, foraminifera, and corals. Davy gave a sample of the polycystine-containing earth to Priscilla Bury. Bury had microscope sides prepared from it that she used to create drawings for a book she was authoring on the Polycystina. In the United States, Mary Booth used sedimentary material from the same Barbados location for making the prepared microscope slides of polycystines that she sold commercially. It is not known if Booth obtained the raw material directly from Davy or through another source.

 How to footnote this page: Reiser, F. W. (2022 November) Ernst Haeckel and the Polycystina Searching an Invisible World for Its Tiniest Things.