Background:

Peridinium quinquecorne is a benthic-planktonic, neritic, tropical-boreal dinoflagellate species, usually with four antapical spines. It exhibits a wide morphological variability, particularly in the number of spines, which has caused a discussion among several authors on its generic position, transferring the species from Peridinium to Blixaea. The genus is currently monotypic. Cells of Blixaea quinquecornis possess a Chaetoceros-like diatom as endosymbiont, which is a unique feature among the so-called “dinotoms” that constitute the family Kryptoperidiniaceae, a well-supported monophyletic group. In Mexican waters, the species is best known from the state of Veracruz, southwestern Gulf of Mexico, where it has caused recurrent blooms; the species has also been reported from other regions of the world.

Methods:

The published literature on the species was revised, with an emphasis on the number of antapical spines.

Goals:

Clarifying the taxonomic status of Blixaea quinquecornis based on the thecal variability.

Results:

In the published literature, the number of the antapical spines emerging from the antapical plates in the dinoflagellate differs among the authors. Both published scanning electron and light microscope images do not allow us to describe the thecal plates in detail and their morphological variability or to conclude if this variability is infra- or interspecific. Our morphological data and the results obtained from the literature do not allow us to confirm the taxonomic status of B. quinquecornis.

Conclusions:

B. quinquecornis probably represents a species complex. Genetic-molecular and thecal-morphological studies are necessary to explain the morphological variability and to characterize different populations of the taxon from different regions through the world.