The species was suggested by Gomez et al. (2017) to be a synonym of Prorocentrum mexicanum . However, the two species differ in both morphology and ecology. P. rhathymum is a benthic marine dinoflagellate with a characteristic pattern of trichocyst pores on the valves, some of which are arranged in radiating lines towards the lateral sides. P. mexicanum is from the marine phytoplankton and has no radiating lines of trichocyst pores, the pores are scattered on the valve surface. See Hoppenrath et al. (2014) for further information on P. rhathymum.
Hoppenrath, M.; Murray, S. A.; Chomérat, N.; Horiguchi, T. (2014). Marine benthic dinoflagellates - unravelling their worldwide biodiversity. <em>Kleine Senckenberg-Reihe.</em> 54: 1-276.
Gomez, F., Qiu, D. & Lin, S. (2017). The synonymy of the toxic dinoflagellates <i>Prorocentrum mexicanum</i> and <i>P. rhathymum</i> and the description of <i>P. steidingerae</i> sp. nov. (Prorocentrales, Dinophyceae). <em>J. Eukaryotic Microbiol. 64: 668-677.</em>