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A new marine benthic toxic Prorocentrum species is described from the tropical/subtropical regions of the Atlantic (Colombian Caribbean Sea and Northeast Brazil) and Pacific (Southern Japan) oceans. Morphological cell structures were examined using light (LM) and scanning electron (SEM) microscopy. Prorocentrum porosum sp. nov. was characterized by 35.9-50.2 μm long and 25.4-45.7 μm deep cells, covered by broadly ovoid symmetric thecal plates. The surface of both thecal plates is smooth and covered by randomly scattered kidney-shaped pores (n = 102-149), rounder towards the center, absent in the central part, and surrounded by a conspicuous marginal ring of about 69-92 evenly spaced pores. Broad V-shaped periflagellar area exhibiting flagellar and accessory pores. The molecular phylogenetic position of P. porosum sp. nov. was inferred using partial LSU rRNA gene (rDNA) and rDNA ITS sequences. This new species branched with high support in a Prorocentrum clade including P. caipirignum, P. hoffmannianum and P. cf. lima (P. lima morphotype 5 sensuZhang et al., 2015). Pairwise comparison of ITS1 and ITS2 transcripts with these closest relatives revealed the presence of compensatory base changes (CBCs), with the exception of P. cf. lima (P. lima morphotype 5), which only showed in ITS2 a hemi-CBC (HCBC) and two base changes that possibly induce a structural modification. Toxin analyses performed in two Colombian and Brazilian strains in the present study detected the presence of low amounts of okadaic acid., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier B.V.)