Prorocentrum pervagatum sp. nov. (Prorocentrales, Dinophyceae): A new, small, planktonic species with a global distribution

Abstract

SUMMARY Prorocentrum comprises a unique group of dinophytes with several apomorphic traits, such as an apical insertion of flagella and the presence of two major, large thecal plates. Species delimitation is challenging, especially for morphologically very similar, small planktonic species. Contemporary analyses, including SEM studies and molecular phylogenetics of type material, are not available for many described species. Based on six strains isolated from Antarctic, subarctic and North Atlantic waters, Prorocentrum pervagatum sp. nov. is described. Prorocentrum pervagatum was small (12–16 μm long and deep), oval to round in outline, and moderately compressed. One small, pyrenoid‐like structure was faintly visible in some cells. Rod‐like, long trichocysts were present. Cells had one distinct apical spine (1.1–1.7 μm in length) visible in light microscopy. The plate surface appeared smooth in light microscopy with few pores located close to the plate margin visible in empty thecae. Electron microscopy revealed plates to be densely covered by small projections and two size classes of thecal pores. Cells had a row of mostly four large pores in apical‐ventral position on the right thecal plate. The periflagellar area consisted of eight small platelets. The apical spine was formed by platelet six. In molecular phylogenetics, P. pervagatum was part of a species group generally exhibiting small size and spiny thecal ornamentation, together with Prorocentrum cordatum and Prorocentrum obtusidens. The new species is distinct in DNA trees and differs from the protologues of other small species of Prorocentrum by the unique combination of size, shape (i.e. only moderately compressed or round), presence of a distinct apical spine, and position of thecal pores (i.e. located at the plate margins only). Its clear description and illustration may stimulate similar work of other small species of Prorocentrum, particularly including the re‐investigation of taxa with historical names collected at the corresponding type localities.

Morphological and Phylogenetic Characterisation of Prorocentrum spinulentum, sp. nov. (Prorocentrales, Dinophyceae), a Small Spiny Species from the North Atlantic

“…The description of Prorocentrum spinulentum provides a scientific name for a small, already recognised and early branching subclade [ 3 , 9 ] of the P. shikokuense species group. Strains of this species group are described as having knob-like short spines on the thecal plate surface [ 4 , 21 , 22 ] and are thus different from P. spinulentum having long spines.…”

“…A systematically representative set of prorocentralean and related accessions was compiled from known reference trees, similarly to a previous approach [ 3 ]. The taxon sample was enriched by all those accessions showing ultimate similarity to the sequences gained from strain 1-D3, as inferred from BLAST searches [ 17 ].…”

“…Prorocentrum Ehrenberg is diverse and comprises predominantly marine species with a worldwide distribution [ 1 , 2 ]. Identification of small (<20 µm), planktonic species of Prorocentrum is challenging [ 3 ]. They are inconspicuous, and differentiating traits, such as surface ornamentation of thecal plates, number and distribution of thecal pores and the presence/absence of apical projections, are difficult to observe unambiguously in light microscopy (LM).…”

“…They are inconspicuous, and differentiating traits, such as surface ornamentation of thecal plates, number and distribution of thecal pores and the presence/absence of apical projections, are difficult to observe unambiguously in light microscopy (LM). Moreover, most small species of Prorocentrum have been described a long time ago, and thus, detailed information on morphology or DNA sequence data linked to the types, or other original material, are lacking [ 3 ].…”

“…The description of the new small, planktonic species Prorocentrum pervagatum Tillmann, Hoppenrath & Gottschling is based on multiple cultured strains from geographically distant localities and by combining high resolution LM and SEM with DNA sequence information [ 3 ]. Only a short time later, another small species, P. thermophilum F.Gómez, Tangcheng Li, Hu.Zhang & Senjie Lin, was described, together with other strains of P. pervagatum (= P. criophilum Gourvil & Gutiérrez-Rodríguez, syn.…”