Polykrikaceae
| Polykrikaceae | |
|---|---|
| A light micrograph of a bullet-shaped cell with a large spiral filament (the extruded nematocyst). | |
| A light micrograph of Polykrikos kofoidii showing an extruded nematocyst. Scale bar = 10µm.[1] | |
| Scientific classification Edit this classification | |
| Domain: | Eukaryota |
| Clade: | Sar |
| Superphylum: | Alveolata |
| Phylum: | Dinoflagellata |
| Class: | Dinophyceae |
| Order: | Gymnodiniales |
| Family: | Polykrikaceae Kofoid & Swezy, 1921 |
| Genera | |
The Polykrikaceae (also known as Polykrikidae) are a family of athecate dinoflagellates of the order Gymnodiniales. Members of the family are known as polykrikoids. The family contains two genera: Polykrikos and Pheopolykrikos.[2]
Characteristics
[edit | edit source]The most distinctive feature of polykrikoids is their formation of multinucleate "pseudocolonies" consisting of an even number of subunit zooids. The two genera differ in number of nuclei; possessing two nuclei regardless of the number of zooids is a synapomorphy for Polykrikos, whereas Pheopolykrikos possess equal numbers of nuclei and zooids.[3]
Along with the Warnowiaceae (warnowiids), polykrikoids are known for possessing unusually complex subcellular structures. In particular, an extrusome complex of two organelles called the nematocyst and taeniocyst is considered a synapomorphy for Polykrikos.[1][3] Molecular phylogenetics studies suggest some inconsistency in the taxonomy of this group, particularly in the assignment of species to one of the two genera.[4][5]
Habitat and life cycle
[edit | edit source]Most polykrikoids are planktonic, although one species - P. lebourae - is benthic.[3] The family includes photosynthetic, heterotrophic, and mixotrophic species.[6] Some species, such as P. kofoidii, are of scientific interest due to their status as predators of other dinoflagellates, a behavior that is significant in the regulation of algal blooms.[6][7][8] Others, such as Ph. hartmanii (which has been reclassified P. hartmanii)[5] are themselves causes of ichthyotoxic algal blooms.[9] P. hartmanii is capable of both heterothallic (outcrossing) and homothallic (self-fertilizing) sexual reproduction.[10]
The reproductive behaviors of polykrikoids are mostly not well understood, although P. kofoidii has been studied and found to have a complex life cycle of both vegetative (asexual) and sexual reproduction complicated by its pseudocolonial structure.[11]
Evolution
[edit | edit source]The family demonstrates a complex evolutionary history indicating multiple instances of loss of photosynthetic plastids in different lineages.[6] The distinctive pseudocolonial structure may have arisen in multiple evolutionary lineages from ancestors capable of forming chains of distinct individual cells.[3]
References
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- ^ Z Chai, Z Hu, Y Liu, Y Tang 2020. Proof of homothally of Pheopolykrikos hartmannii and details of cyst germination process Journal of Oceanology and Limnology 38 (1), 114-123
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