This study presents the first record of a living dinoflagellate cyst with a hypocystal, antapical archeopyle. It is also the first
detailed account of the archeopyle of a living freshwater cyst from the genus Peridinium. The cysts were isolated from sediment
traps deployed in Lake Nero di Cornisello, a low-alkalinity high mountain lake of the Adamello mountain range (2233m
above sea level, South Eastern Alps, Italy). The archeopyle is large, clearly hypocystal, polygonal, and slightly peanut-shaped.
The species producing this cyst belongs to the Peridinium umbonatum group and is described based on scanning electron
microscopy and light microscopy. Partial sequences of SSU rDNA were obtained and compared with previously published
sequences from the P. umbonatum group. The taxonomic position of the species is discussed.