Ernst Haeckel was the first to depict dinoflagellate parasites in a tintinnid ciliate. He thought the ciliate was forming embryo

From the description of Cyttarocylis cassis (as Dictyocysta cassis). The figure is a combination of two images in plate 7 of Haeckel 1873, available on the Aquaparadox site: 'Classic Taxonomic Monographs'. The 1873 by paper by Ernst Haeckel was the first article ever published which was devoted entirely to tintinnid ciliates.