The naked marine dinoflagellates Proterythropsis vigilans, Nematodinium armatum, and Nematodinium torpedo are reported for the first time in the Gulf of California. The first and the third species are also recorded for the first time on the Pacific coast of Mexico. They were recorded during winter-spring in seawater at 20-26.5°C. Nematodinium armatum was the most frequent species. Proterythropsis vigilans was less frequent. The 3 species were found in phytoplankton net samples. No quantitative data are reported here. A short description is given for each species, and micrographs provide information about the main morphological characteristics.