Since spliced-leader (SL) trans-splicing occurs throughout the phylum Dinoflagellata (e.g. [8] - [11] ) yet has not been found in apicomplexans and ciliates, SL trans-splicing appears to be unique to the dinoflagellates within the Alveolata [12] . Under this scenario, the presence of SL trans-splicing in Perkinsus spp. [8] , [13] allies Perkinsus spp. with dinoflagellates. While dinoflagellates use a 22-nt conserved SL (DinoSL), P. marinus harbors a longer (22 nt) and a shorter (21 nt) SL, with sequences varying slightly from the canonical DinoSL [14] . In addition, the genome of P. marinus (,86 million base pairs; Project ID: 12736, http://www.ncbi.nlm. nih.gov/genomeprj/46451) is closer in overall size to apicomplexans (9-60 million base pairs; http://www.ncbi.nlm.nih.gov/genomeprj), but orders of magnitude smaller than dinoflagellates (3-250 billion base pairs; e.g. [15] , [16] ), and P. atlanticus chromosomes are more like typical eukaryotic chromosomes than dinokaryotic chromosomes [17] . Thus, whether Perkinsus spp. should be considered dinoflagellates remains unresolved.