Ernst Haeckel elaborated a system of classification of the radiolarians in a series of three classic papers -
Haeckel, E. 1862. Die Radiolarien (Rhizopodia Radiaria), xiv + 572 pp.; Atlas, iv + 35 pls., Reimer, Berlin.
This monograph is based largely on plankton samples that he collected at Messina, and the taxonomic system is strongly influenced by the work of his teacher Johannes Mueller. Haeckel did not at that time have access to good fossil radiolarian assemblages, and had no high opinion of the work of the father of 'Mikrogeologie', C.G. Ehrenberg.
Haeckel, E. 1881. Entwurf eines Radiolarien-Systems auf Grund von Studien der Challenger-Radiolarien Jenaische Zeitschrift fur Naturwissenschaft, vol.15 (new ser., vol.8), part 3, pp.418-472.
Known to his contemporaries as the "Prodromus" (a word appearing only in the heading of its main part, comprising Latin definitions of taxa from order to genera), this work was written hallfway through Haeckel's ten-year study of the radiolarians collected by the Challenger Expedition. He revealed the outlines of the rather comprehensive, geometric system of classification that he would use for the Challenger radiolarians. A brief extract, translated (by my classically-inclined wife) and somewhat simplified, follows -
Tribe Astracturida
Unnamed first subtribe with two arms, comprising the genera Diplactura (with the arms free) and Amphactura (with the arms joined)
Unnamed second subtribe with three arms, comprising the genera Trigonactura (with the arms free) and Hymenactura (with the arms joined)
Unnamed third subtribe with four arms, comprising the genera Astractura (with the arms free) and Stauractura (with the arms joined)
and so on.
Haeckel, E. 1887. Report on the Radiolaria collected by H.M.S. Challenger during the years 1873-1876. Rep. Sci. Results, H.M.S. Challenger 1873-6, Zoology, vol.18, 2 parts, clxxxviii + 1803 pp., Atlas.
The general outlines of the 1881 classification carry over into this Challenger Report, though with some amplification and re-arrangement. The 1887 system of generic definition was so geometrically simple and comprehensive that it continued to be used until the middle of the twentieth century, though several authors had pointed out that was not a "natural" system - for example, less completely developed specimens of a species would be assigned to a different genus or family than would more completely developed individuals of the same species. The very bulk of the system (the Challenger Report recognized 739 genera) constituted an impediment to its piecemeal replacement, and many early-twentieth-century workers unquestioningly adopted the same morphological characters used by Haeckel as being "taxonomically important". It was only in the second half of this century, when evolutionary lineages were revealed through the study of stratigraphic sequences, that "natural" famili! es and genera began to replace the artificial ones erected by Haeckel, and new ways of viewing radiolarian skeleton morphology became inevitable.
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