Diagnosis_Genus: These parasites were initially confounded with a putative formation of anisospores during sexual reproduction of radiolarian by Hertwig 1879 and Brandt 1885. Chatton 1923 erected a new genus (Merodinium) for all Syndinium-like parasites infesting radiolarian, then separating parasites of copepods  from the ones infecting radiolarian. This separation is based on the mode of infection (intracellular in Merodinium and in the general cavity of copepods), by the earlier fragmentation of the plasmodium in Merodinium, and the shape of their spores (fusiform in Syndinium and piriform for Merodinium). Hollande and Enjumet 1953 kept the genus name Syndinium for all parasites of radiolarian located inside the capusle, and reserved the genus name of Merodinium for all extracapsular parasites. Merodinium and Syndinium were considered as synonymous two years after by Hollande and Enjumet 1955. Delineation of these two genera, if valid, needs to be more studied. Species were mainly separated based upon the identity of their host species.
Diagnosis_Species: S. brandti Hovasse 1923. Intracapsular parasite of Collozoum inerme. First stage unknown. Young trophonts intracapsular, forming plasmodium that fragmented. These sporonts migrate at the periphey of the capsule (forming a rosace), the host nucleus remaining in the central place. Two type of spores are produced (macro and microspores). V-shaped chromosomes (5 in total). Detected all the year.