Octactis

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Octactis
Dictyocha speculum Stohr 1880 Palaeontogr vol xxvi Taf vii fig 8.png
Illustration of Octactis speculum silica skeletons by Stöhr (1880) [1]
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Stramenopiles
Phylum: Gyrista
Subphylum: Ochrophytina
Class: Dictyochophyceae
Order: Dictyochales
Family: Dictyochaceae
Genus: Octactis
Schiller, 1925 [2] emend. F.H.Chang, J.M.Grieve & J.E.Sutherland, 2017 [3]
Species [3]

Octactis is a genus of silicoflagellates, [3] marine photosynthetic unicellular protists that take the form of either flagellates or axopodial amoebae. [4] Described by Josef Schiller in 1925, Octactis contains various species of marine phytoplankton, some of them responsible for algal blooms that are toxic to fish. [5]

Contents

Characteristics

Octactis species are unicellular protists that appear as several different multinucleate forms (i.e. with multiple nuclei). The most prevalent form is as amoebae surrounded by an external, basket-like siliceous skeleton, consisting of two conspicuous rings: a smaller apical ring supported by short struts that are attached to a larger basal ring. The skeleton pikes sometimes occur on the surface of the basal ring. The large window that the apical ring encloses is undivided. Other forms also present are naked amoebae and sometimes mucocyst-bearing amoebae. Both skeleton-bearing and naked cells present a long flagellum. The mucocysts appear on the periphery of skeleton-bearing cells, absent in the naked cells. [3]

Within each Octactis cell there is a pyrenoid embedded within a chloroplast. The chloroplast has a short thylakoid intrusion. The skeleton-bearing cells contain between 6 and 8 Golgi bodies. The chloroplasts contain all three accessory chlorophylls, c1, c2 and c3, as well as fucoxanthin as the main carotenoid, with diadinoxanthin and one or two oxyfucoxanthin derivatives. They lack lutein. [3]

Ecology

Octactis species are unicellular algae found in typically cold marine waters as part of the phytoplankton. Like other silicoflagellates, Octactis cells are surrounded by a siliceous skeleton composed of various spikes arranged in specific shapes. [6] One species, O. speculum , is considered harmful for marine fauna, due to appearing in harmful algal blooms that have caused high mortality of fish such as salmon and trout. The silica skeletons provoke irritation and secretion of mucus in fish gills, which leads to death. It has also been suggested that the mortality was caused by excessive cellular respiration during algal blooms of O. speculum, which decreased the dissolved oxygen in the water. [5]

Systematics

Taxonomic history

The genus Octactis was described in 1925 by phycologist Josef Schiller as a member of the Silicoflagellata, [2] now known as the order Dictyochales, a group of stramenopile algae with siliceous skeletons. [6] Several species have been described, but they have been rearranged between this genus and two more genera, Dictyocha and Stephanocha (formerly under the invalid Distephanus name due to being homonymous with the flowering plant Distephanus ) [7] multiple times. [3]

The first Octactis species to be described was O. pulchra, proposed by Schiller himself in 1925. It was described from superficial marine samples of the middle to southern Adriatic Sea, and remained its type and only species. In 1985 the entire genus with all its species were synonymised to Distephanus [8] (later Stephanocha ). [7] On the basis of molecular phylogeny, researchers in 2017 emended the definition of Octactis and transferred two species of Dictyocha , D. octonaria and D. speculum, to it. [3]

Classification

There are two species of Octactis currently accepted: [3]

 = Dictyocha octonariaEhrenberg, 1844
 = Dictyocha speculumEhrenberg, 1839
 = Distephanus speculum(Ehrenberg, 1839) Haeckel, 1887
 = Stephanocha speculum(Ehrenberg, 1839) McCartney & R.W.Jordan, 2015 [7]

Related Research Articles

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<span class="mw-page-title-main">Dictyochales</span> Order of single-celled organisms

The silicoflagellates are a small group of unicellular photosynthetic protists, or algae, belonging to the supergroup of eukaryotes known as Stramenopiles. They behave as plankton and are present in oceanic waters. They are well-known from harmful algal blooms that cause high mortality of fish. Additionally, they compose a rich fossil record represented by their silica skeletons.

<span class="mw-page-title-main">Axodine</span> Class of single-celled organisms

The axodines are a group of unicellular stramenopiles that includes silicoflagellate and rhizochromulinid algae, actinomonad heterotrophic flagellates and actinophryid heliozoa. Alternative classifications treat the dictyochophytes as heterokont algae, or as Chrysophyceae. Other overlapping taxonomic concepts include the Actinochrysophyceae, Actinochrysea or Dictyochophyceae sensu lato. The grouping was proposed on the basis of ultrastructural similarities, and is consistent with subsequent molecular comparisons.

<span class="mw-page-title-main">Phaeodarea</span> Class of protists

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<span class="mw-page-title-main">Microfossil</span> Fossil that requires the use of a microscope to see it

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<span class="mw-page-title-main">Euglyphida</span> Order of single-celled organisms

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<span class="mw-page-title-main">Ochrophyte</span> Phylum of algae

Ochrophytes, also known as heterokontophytes or stramenochromes, are a group of algae. They are the photosynthetic stramenopiles, a group of eukaryotes, organisms with a cell nucleus, characterized by the presence of two unequal flagella, one of which has tripartite hairs called mastigonemes. In particular, they are characterized by photosynthetic organelles or plastids enclosed by four membranes, with membrane-bound compartments called thylakoids organized in piles of three, chlorophyll a and c as their photosynthetic pigments, and additional pigments such as β-carotene and xanthophylls. Ochrophytes are one of the most diverse lineages of eukaryotes, containing ecologically important algae such as brown algae and diatoms. They are classified either as phylum Ochrophyta or Heterokontophyta, or as subphylum Ochrophytina within phylum Gyrista. Their plastids are of red algal origin.

<i>Karenia</i> (dinoflagellate) Genus of single-celled organisms

Karenia is a genus that consists of unicellular, photosynthetic, planktonic organisms found in marine environments. The genus currently consists of 12 described species. They are best known for their dense toxic algal blooms and red tides that cause considerable ecological and economical damage; some Karenia species cause severe animal mortality. One species, Karenia brevis, is known to cause respiratory distress and neurotoxic shellfish poisoning (NSP) in humans.

<span class="mw-page-title-main">Testate amoebae</span>

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<i>Dinophysis</i> Genus of single-celled organisms

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<i>Dinobryon</i> Genus of algae

Dinobryon is a type of microscopic algae. It is one of the 22 genera in the family Dinobryaceae. Dinobryon are mixotrophs, capable of obtaining energy and carbon through photosynthesis and phagotrophy of bacteria. The genus comprises at least 37 described species. The best-known species are D. cylindricum and D. divergens, which come to the attention of humans annually due to transient blooms in the photic zone of temperate lakes and ponds. Such blooms may produce volatile organic compounds (VOCs) that produce odors and affect water quality.

<span class="mw-page-title-main">Marine microorganisms</span> Any life form too small for the naked human eye to see that lives in a marine environment

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<span class="mw-page-title-main">Vampyrellida</span> Order of single-celled organisms

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<span class="mw-page-title-main">Nassellaria</span> Order of single-celled organisms

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References

  1. Stöhr, Emil. "Die Radiolarienfauna der Tripoli von Grotte Provinz Girgenti in Sicilien" (PDF). Palaeontographica. 2: 69–124.
  2. 1 2 Schiller, Jos. "Die planktontischen Vegetationen des Adriatischen Meeres. B. Chrysomonadina, Heterokontae, Cryptomonadina, Eugleninae, Volvocales. 1. Systematischer Teil" (PDF). Archiv für Protistenkunde. 53: 59–123.
  3. 1 2 3 4 5 6 7 8 Chang, Fook Hoe; Sutherland, Judy; Bradford-Grieve, Janet (2017). "Taxonomic revision of Dictyochales (Dictyochophyceae) based on morphological, ultrastructural, biochemical and molecular data". Phycological Research. 65 (3): 235–247. doi:10.1111/pre.12181. S2CID   89818534.
  4. Moestrup, Øjvind; O'Kelly, Charles J. (2000). "Class Silicoflagellata Lemmermann, 1901" (PDF). In Lee, John J.; Leedale, Gordon F.; Bradbury, Phyllis (eds.). An Illustrated Guide to the Protozoa. Vol. II (2nd ed.). Lawrence, Kansas: Society of Protozoologists. pp. 775–782.
  5. 1 2 Prego, Ricardo; Carballeira, Rafael; Pazos, Yolanda; Bao, Roberto (2023). "Oceanographical Context of the First Bloom of the Silicoflagellate Octactis speculum (Ehrenberg) Recorded to Cause Salmon Mortality in a Galician Ria: Was This Bloom a Rare Event in the Iberian Coast?". Toxins. 15 (7): 435. doi: 10.3390/toxins15070435 . PMC   10467100 . PMID   37505704.
  6. 1 2 Lee, R.E. (2008). "14. Heterokontophyta: Dictyochophyceae". Phycology. Cambridge University Press. pp. 359–364. ISBN   978-1-139-46987-6.
  7. 1 2 3 Jordan, Richard; McCartney, Kevin (2015). "Stephanocha nom. nov., a replacement name for the illegitimate silicoflagellate genus Distephanus (Dictyochophyceae)". Phytotaxa. 201 (3): 177. doi:10.11646/phytotaxa.201.3.1.
  8. Ling, Hsin Yi; Takahashi, Kozo (1985). "The silicoflagellate genus Octactis Schiller 1925: A synonym of the genus Distephanus". Micropaleontology. 31 (1): 76–81. Bibcode:1985MiPal..31...76L. doi:10.2307/1485583. JSTOR   1485583.