Diagnosis_Genus: Solenodinium Chatton 1923. Intracapsular parasites of thalassicoles, forming digitated plasmodia invading the host endoplasma. V-shaped chromosome typical for Syndiniales during sporogenesis.

Diagnosis_Species: S. leptotaenia Hovasse & Brown 1953. Young trophont produced short discontinuous digitations inside the endoplasm, oriented from the interior to the exterior of the capsule, but that do not cross the host nucleus. Trichocysts present in the plasmodium. Nuclei are sparse and arranged in 1-2 files inside digitations. Plasmodia and nuclei increase in size and number, whilst the nucleus often disappear. Sporogenesis produced two types of spores (macro- and microspores), but only one type was observed per infection. V-shaped chromosome (5 in total).