Extant species of the dinoflagellate genus Gonyaulax are capable of producing resting cysts morphologically similar to different cyst-based genera, and their cyst-theca relationships are far from resolved. Here we have carried out germination experiments on several living cysts that resemble Spiniferites delicatus from the subtropical regions of China and Mexico. Both cyst and theca morphology were examined by light and scanning electron microscopy. A new species, Gonyaulax pospelovana, is described, characterized by a cingulum displacement and an overhang of twice its width, and two short antapical spines. The cysts of G. pospelovana had a granular surface and gonal processes with petaloid tips. Maximum likelihood and Bayesian inference analyses based on LSU and SSU rRNA gene sequences revealed that strains identified as G. pospelovana were monophyletic, forming a sister clade to Gonyaulax ellegaardiae and several presumable strains of Gonyaulax spinifera. One Chinese strain and two Mexican strains of G. pospelovana were examined for yessotoxin production using LC-MS/MS, but were not found to produce a detectable amount of toxins. Metabarcoding targeting the 18S V4 rRNA gene was performed on monthly collected samples in Xiamen Bay, China. A ZOTU (zero-radius operational taxonomic units) was detected that was consistent with G. pospelovana. Its maximum abundance was recorded in summer. Additionally, an OTU was identified as G. pospelovana from the Tara Oceans metabarcoding data, which occurred in the Indian and Pacific oceans at temperatures ranging from 28°C to 31°C, suggesting that it is a warm water species.