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Coolia
Genus of dinoflagellates of the family Ostreopsidaceae From Wikipedia, the free encyclopedia
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Coolia is a marine dinoflagellate genus in the family Ostreopsidaceae. It was first described by Meunier in 1919.[1] There are currently seven identified species distributed globally in tropical and temperate coastal waters.[2] Coolia is a benthic or epiphytic type dinoflagellate: it can be found adhered to sediment or other organisms but it is not limited to these substrates.[3] It can also be found in a freely motile form in the water column.[3][4] The life cycle of Coolia involves an asexual stage where the cell divides by binary fission and a sexual stage where cysts are produced.[5] Some of the species, for example, Coolia tropicalis and Coolia malayensis, produce toxins that can potentially cause shellfish poisoning in humans.[6]
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Etymology
The genus was named after a Pharmacist, M. Cool, from Nieupoort, Belgium, where the first species of the genus Coolia, Coolia monotis was originally discovered in the oyster beds.[1]
Taxonomy
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Coolia was first described by Alphonse Meunier (1919).[1] At the time of discovery, it was placed in its own monospecific genus.[7] At that time, the only species identified was Coolia monotis, which was discovered in oyster beds and the waters surrounding Nieupoort, Belgium.[1]
Between 1928 and 1956, Coolia monotis was placed in the same genus as Ostreopsis species, which is a genus also in the family Ostreopidaceae, because Coolia and Ostreopsis have similar patterns on their epithecae.[5][7] In 1956 however, because of distinct differences in the hypotheca, it was put back into its individual genera in the family Ostreopidaceae.[7]
Coolia monotis remained the only species in the Coolia until 1995. In 1995, Coolia tropicalis was described.[8] In 2000, Coolia areolata was described.[4] In 2008, Coolia canariensis was described.[9] In 2010, Coolia malayensis was described.[10] Most recently in 2015, Coolia santacroce and Coolia palmyrensis were described.[11]
Species include:
- Coolia areolata
- Coolia canariensis
- Coolia malayensis
- Coolia monotis
- Coolia tropicalis
- Coolia santacroce
- Coolia palmyrensis
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Description
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Morphology
Coolia has small spherical cells and is anteroposteriorly compressed.[1][5][4][12] The cell size varies based on the species, but they have been typically reported to be approximately between 23-50 μm in length and 21-45 μm wide.[5][8][3] Coolia cells are distinguished by having a round hypotheca that is larger than their round epitheca.[5][8][7]
Coolia has plates covering the thecal surface that have an irregular pattern and are various sizes.[8][4][12] In most species, the thecal surface contains intercalary bands and is smooth and covered with large thecal pores that are round and ovoid.[5][4][10] Another distinguishing feature to identify Coolia is a plate on the epitheca that is off centred and contains an apical pore complex with a long, curved pore that has a slit containing two costae.[5] This apical pore is often visible because of its large size.[5] Coolia also has an ellipsoidal-shaped ventral pore on the ventral surface.[5]
From a dorsal view of the cell, the lipped cingulum (located equatorially) can be viewed.[5] The cingulum is narrow and the inside surface has round pores with smooth edges. There are also marginal pores surrounding the lipped cingulum.[5] Coolia also has a narrow sulcus that contains relatively short longitudinal flagellum at the posterior end.[5] As Coolia is photosynthetic, it contains golden-brown discoid chloroplasts.[5] The cells also only contain one nucleus with condensed chromosomes in the hypocone.[5]
Life cycle
Coolia has an asexual and a sexual life cycle. It is thought that under low nutrients, low light, or low temperature conditions, sexual reproduction may be initiated, resulting in the production of a resting cyst.[5][12]
Cells divide asexually by binary fission.[5] The division process begins as the single nucleus with condensed chromosomes elongates and two nuclei develop parallel to each other.[5] Before dividing into daughter cells, the dividing cells stay attached to each other for approximately 12-24 hours.[5] The doubling time of Coolia is approximately 3-4 days[5]
Sexual reproduction occurs as gametes begin to form in the population; this is an irreversible transition.[5] Gametes move around each other rapidly and then align laterally, forming gamete pairs with the girdle and sulcus contacting each other, forming a fertilization bridge.[5] A planozygote is formed when the cells stop moving and the fertilization bridge disappears, allowing the two nuclei to join together. This indicates that karyogamy has occurred.[5] The theca then begins to develop and the cell becomes motile.[5] As the planozygote matures, it shrinks and becomes immobile, eventually developing into a cyst.[5] The cyst further develops to contain a single nucleus that makes up much of the volume of the cell.[5] At the end of the process, meiosis occurs.[5] The sexual life cycle is thought to last approximately 2 months.[5]
Genetics
Phylogenetic analysis of different regions of rDNA supports the separate genus’ for Ostreopsis and Coolia. Analysis of 5.8S rDNA-ITS sequence alignments from European and Asian isolates and their out-groups supports distinct lineages of Ostreopsis and Coolia.[7] Lineages of Ostreopsis from Europe and Asia are genetically isolated and separate from lineages of Coolia from Europe and Asia.[7] This indicates that the lineages of Ostreopsis and Coolia evolved independently.[7] Additionally, analysis of LSU rDNA data shows that all the species of Coolia share a more recent common ancestor with each other than they do with Ostreopsis, who share a more recent common ancestor with other species in its genus.[3]
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Habitat and ecology
Coolia is found globally in coastal marine regions of both temperate and tropical waters.[2] Coolia monotis have a large habitat range and is found in tropical, sub-tropical, and temperate regions, whereas other species such as Coolia areolata and Coolia tropicalis have a more restricted range and are typically found in tropical regions.[7]
Coolia is typically a benthic type organism and can be attached to sandy substrates, coral, or brown and red seaweed.[4][10][3] In addition, it also can act as a planktonic organism and form blooms in the water column.[3]
Coolia, especially in tropical regions, forms assemblages with Gambierdiscus toxicus; thus, they are often falsely described as being responsible for causing ciguatera.[11][7] Ciguatera is actually caused by Gambierdiscus toxicus, not Coolia.[7][11]
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Human importance
Coolia is considered a toxic dinoflagellate genus. Some of the species are known to be toxic and produce harmful algal blooms (HABs) that are of potential concern to human health.[6] They produce yessotoxins.[7] The species that are known to produce the toxins are Coolia tropicalis, Coolia malayensis, Coolia santacroce and Coolia palmyrensis.[6][11] However, it is possible other species of the genus also produce toxins.
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References
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