Clarifying confusion–Prorocentrum triestinum J.Schiller and Prorocentrum redfieldii Bursa (Prorocentrales, Dinophyceae) are two different species

The Prorocentrales are a unique group of dinophytes based on several apomorphic traits, but species delimitation is challenging within the group. Prorocentrum triestinum was described by Josef Schiller in 1918 as an important bloom-forming species from Trieste (Mediterranean, Adriatic Sea) with a conspicuous asymmetric outline and a small, asymmetrically located subapical spine. All subsequent records under this name fail to conform to Schiller’s original description. These inconsistencies have their origin in John Dodge’s 1975 revision of Prorocentrum, which placed Prorocentrum redfieldii, a more symmetrical, slender species with a long apical spine, into synonymy under P. triestinum. To clarify this confusion, we collected samples at the type locality of P. triestinum in Trieste and established a strain that is morphologically consistent with the protologue and suitable for use in epitypification. Morphology and rRNA sequence data of this strain were compared with four new strains id...