Dinophyceae

The Dinophyceae (Dinophyceae) are a group of unicellular protists of the superclass Dinoflagellata that includes species of dinoflagellates whose nucleus remains dinokaryotic throughout the cell cycle, which is dominated by the haploid stage. Includes all typical dinoflagellates, such as Peridinium and Gymnodinium, plus more unusual ones, including some colonial, ameboid, or parasitic ones.

Dinophyceae (Desmophyceae) are unicellular organisms, most of them biflagellate, although aflagellate forms may appear: coccoid, filamentous, palmeloid or amoeboid, related to the great variety of forms of nutrition. Generally photosynthetic, although there are also heterotrophic forms: saprophytic, parasitic, symbiotic, and holozoic. Many marine autotrophs are auxotrophs for various vitamins.

The cell wall or theca, when present, is composed mainly of cellulose. They have two flagella, located in grooves or depressions on the cell surface. An acronematic flagellum (smooth, ending in a fibril), posteriorly arranged, located in a longitudinal groove or sulcus. Another ribbon-shaped flagellum, located in a transverse groove, cingulate, equatorially, which allows rotation and displacement. As pigments they present chlorophyll a and c, β-carotene, xanthophylls, peridinin, neoperidinin, dinoxanthin, neodinoxanthin and diatoxanthin. The reserve material is starch.

Dinophyceans are classified by their morphology. Species with theca are divided into four orders, based on the arrangement of their armor plates: Peridiniales (eg Peridinium), Gonyaulacales (eg Ceratium, Gonyaulax), Dinophysiales (eg Dinophysis) and Prorocentrales (eg Prorocentrum). The Peridiniales are probably paraphyletic relative to the others and in rRNA trees are mixed with species lacking theca. Non-theca groups are considered to be polyphyletic and are classified into several orders. Examples of genera are Gymnodinium, Amphidinium, Symbiodinium, and Dinamoeba.

A group of dinokaryon-bearing parasitic dinoflagellates, Blastodiniophyceae, has been invalidated. It included, among others, the well-known genus Pfiesteria, as well as Oodinium and Haplozoon , which are now distributed among several orders of Dinophycea.

Origin

A process of symbiogenesis would be involved in the origin of the Dinophyceans, given by the biological fusion between a heterotrophic predatory dinoflagellate that became the host of an endosymbiont haptophyte alga. Due to this, the typical plastids of Dinophyceans have inherited the presence of chlorophylls a, c1, c2, c3, β-carotene and various xanthophylls. Both the peridinin-possessing groups, which make up the majority, and the fucoxanthin-possessing Brachidiniales, are related to this monophyletic origin.

Phylogeny

Part of the subgroups would be related as follows:

The appearance of the typical theca of the Dinophyceans would have been a unique event, so the theca dinoflagellates would form a monophyletic group. This theca consists of cellulose plates within the subcuticular alveoli.