Cis-splicing is thought to be uncommon in dinoflagellates [2] ; however, only a few dinoflagellates have been examined for the presence of introns (e.g. form II Rubisco in Symbiodinium [33] , luciferase C in Pyrocystis lunula [34] ). We have examined more than 30 genes such as pcna, form II Rubisco, 14-3-3, and centrin for several dinoflagellates ( [35] , [36] and our unpubl. results), and did not find introns. A relatively high intron density for a dinoflagellate is found in Amphidinium carterae, in which a survey of 31 genes yields a 48% cis-splicing rate [37] . Our analysis of 104 Perkinsus genes yielded a 69.2% cis-splicing rate, a level contrasting those found in most dinoflagellates, and closer to the .50% level found in apicomplexans [38] , [39] .