Peridinioid dinoflagellates, armoured, mostly with chloroplasts; some form red-tides; some produce toxins; mainly marine; distinguished mostly by the arrangement and number of the thecal plates; tabulation follows or is derived from one or both of the following patterns: a) the first apical plate or its homologue (1u) is asymmetrical, its left lateral triple junction being more anterior than the right lateral triple junction and giving a very asymmetrical pore complex; or b) there are 2-4 fundital plates, these always including the posterior intercalary and first antapical plates or their homologues (X and Y). Of these fundital plates 1 (Y) is almost always larger and is more dorsal than the other(s).