# Octactis

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> Source: https://en.wikipedia.org/wiki/Octactis
> Source revision: 1348088303
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{{Short description|Genus of unicellular protists}}
{{Automatic taxobox
| taxon = Octactis
| authority = [Schiller](/source/Josef_Schiller), 1925<ref name="Schiller 1925"/> emend. F.H.Chang, J.M.Grieve & J.E.Sutherland, 2017<ref name="Revision Dictyochales"/>
| image = Dictyocha_speculum_Stöhr_1880_Palæontogr_vol_xxvi_Taf_vii_fig_8.png
| image_caption = Illustration of ''[Octactis speculum](/source/Octactis_speculum)'' silica skeletons by Stöhr (1880)<ref name="Stöhr 1880"/>
| subdivision_ranks = Species
| subdivision_ref = <ref name="Revision Dictyochales"/>
| subdivision =
* ''[O. octonaria](/source/Octactis_octonaria)''
* ''[O. speculum](/source/Octactis_speculum)''
| synonyms_ref =
| synonyms =
| diversity =
}}

'''''Octactis''''' is a genus of [silicoflagellate](/source/silicoflagellate)s,<ref name="Revision Dictyochales"/> [marine](/source/marine_life) [photosynthetic](/source/photosynthetic) unicellular [protist](/source/protist)s that take the form of either [flagellate](/source/flagellate)s or [axopodia](/source/axopodia)l [amoebae](/source/amoebae).<ref name="IGP Silicoflagellata"/>   Described by [Josef Schiller](/source/Josef_Schiller) in 1925, ''Octactis'' contains various species of marine [phytoplankton](/source/phytoplankton), some of them responsible for [algal bloom](/source/algal_bloom)s that are toxic to [fish](/source/fish).<ref name="Prego 2023"/>

== Characteristics ==

''Octactis'' species are [unicellular](/source/unicellular) [protist](/source/protist)s that appear as several different [multinucleate](/source/multinucleate) forms (i.e. with multiple [nuclei](/source/cell_nucleus)). The most prevalent form is as [amoebae](/source/amoebae) surrounded by an external, basket-like [siliceous skeleton](/source/Protist_shell), 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](/source/mucocyst)-bearing amoebae. Both skeleton-bearing and naked cells present a long [flagellum](/source/flagellum). The mucocysts appear on the periphery of skeleton-bearing cells, absent in the naked cells.<ref name="Revision Dictyochales"/>

Within each ''Octactis'' [cell](/source/cell_(biology)) there is a [pyrenoid](/source/pyrenoid) embedded within a [chloroplast](/source/chloroplast). The chloroplast has a short thylakoid intrusion. The skeleton-bearing cells contain between 6 and 8 [Golgi bodies](/source/Golgi_bodies). The chloroplasts contain all three accessory chlorophylls, [c{{sub|1}}](/source/chlorophyll_c1), [c{{sub|2}}](/source/chlorophyll_c2) and [c{{sub|3}}](/source/chlorophyll_c3), as well as [fucoxanthin](/source/fucoxanthin) as the main [carotenoid](/source/carotenoid), with [diadinoxanthin](/source/diadinoxanthin) and one or two [oxyfucoxanthin](/source/oxyfucoxanthin) derivatives. They lack [lutein](/source/lutein).<ref name="Revision Dictyochales"/>

== Ecology ==

''Octactis'' species are [unicellular](/source/unicellular) [algae](/source/algae) found in typically cold marine waters as part of the [phytoplankton](/source/phytoplankton). Like other silicoflagellates, ''Octactis'' cells are surrounded by a [siliceous skeleton](/source/Protist_shell) composed of various spikes arranged in specific shapes.<ref name="Lee Dictyochophyceae"/> One species, ''[O. speculum](/source/Octactis_speculum)'', is considered harmful for marine fauna, due to appearing in [harmful algal bloom](/source/harmful_algal_bloom)s that have caused high mortality of fish such as [salmon](/source/salmon) and [trout](/source/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](/source/cellular_respiration) during algal blooms of ''O. speculum'', which decreased the [dissolved oxygen](/source/dissolved_oxygen) in the water.<ref name="Prego 2023"/>

== Systematics ==

=== Taxonomic history ===

The [genus](/source/genus) ''Octactis'' was described in 1925 by [phycologist](/source/phycologist) [Josef Schiller](/source/Josef_Schiller) as a member of the [Silicoflagellata](/source/Silicoflagellata),<ref name="Schiller 1925"/> now known as the order [Dictyochales](/source/Dictyochales), a group of [stramenopile](/source/stramenopile) [algae](/source/algae) with [siliceous skeletons](/source/Protist_shell).<ref name="Lee Dictyochophyceae"/> Several species have been described, but they have been rearranged between this genus and two more genera, ''[Dictyocha](/source/Dictyocha)'' and ''[Stephanocha](/source/Stephanocha)'' (formerly under the invalid ''Distephanus'' name due to being homonymous with the [flowering plant](/source/flowering_plant) ''[Distephanus](/source/Distephanus)'')<ref name="Stephanocha"/> multiple times.<ref name="Revision Dictyochales"/>

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](/source/Adriatic_Sea), and remained its [type](/source/type_species) and only species. In 1985 the entire genus with all its species were synonymised to ''Distephanus''<ref name="Ling & Takahashi 1985"/> (later ''[Stephanocha](/source/Stephanocha)'').<ref name="Stephanocha"/> On the basis of [molecular phylogeny](/source/molecular_phylogeny), researchers in 2017 [emended](/source/Circumscription_(taxonomy)) the definition of ''Octactis'' and transferred two species of ''[Dictyocha](/source/Dictyocha)'', ''D. octonaria'' and ''D. speculum'', to it.<ref name="Revision Dictyochales"/>

=== Classification ===

There are two species of ''Octactis'' currently accepted:<ref name="Revision Dictyochales"/>

* ''[Octactis octonaria](/source/Octactis_octonaria)'' {{au|(Ehrenberg, 1844) Hovasse, 1946}}
: &nbsp;= ''Dictyocha octonaria'' {{au|Ehrenberg, 1844}}
* ''[Octactis speculum](/source/Octactis_speculum)'' {{au|(Ehrenberg, 1839) F.H.Chang, J.M.Grieve & J.E.Sutherland, 2017}}
: &nbsp;= ''Dictyocha speculum'' {{au|Ehrenberg, 1839}}{{br}}&nbsp;= ''Distephanus speculum'' {{au|(Ehrenberg, 1839) Haeckel, 1887}}{{br}}&nbsp;= ''Stephanocha speculum'' {{au|(Ehrenberg, 1839) McCartney & R.W.Jordan, 2015}}<ref name="Stephanocha"/>

== References ==
<references>

<ref name="Stöhr 1880">{{cite journal | title = Die Radiolarienfauna der Tripoli von Grotte Provinz Girgenti in Sicilien | first1 = Emil | last1 = Stöhr | journal = Palaeontographica | volume = 2 | pages = 69–124 | url = http://aquaparadox.obs-vlfr.fr/html/PFD/Taxonomic%20Monographs/Stohr1880.pdf }}</ref>

<ref name="Schiller 1925">{{cite journal | title = Die planktontischen Vegetationen des Adriatischen Meeres. B. Chrysomonadina, Heterokontae, Cryptomonadina, Eugleninae, Volvocales. 1. Systematischer Teil. | first1 = Jos. | last1 = Schiller | journal = Archiv für Protistenkunde | volume = 53 | pages = 59–123 | url = https://www.zobodat.at/pdf/Archiv-fuer-Protistenkunde_53_1926_0059-0123.pdf }}</ref>

<ref name="Revision Dictyochales">{{cite journal | first1 = Fook Hoe | last1 = Chang |first2 = Judy | last2 = Sutherland | first3 = Janet | last3 = Bradford-Grieve | title = Taxonomic revision of Dictyochales (Dictyochophyceae) based on morphological, ultrastructural, biochemical and molecular data | journal = Phycological Research | date = 2017 | volume = 65 | issue = 3 | pages = 235–247 | doi = 10.1111/pre.12181| s2cid = 89818534 }}</ref>

<ref name="IGP Silicoflagellata">{{cite book | chapter = Class Silicoflagellata Lemmermann, 1901 | first1 = Øjvind | last1 = Moestrup | first2 = Charles J. | last2 = O'Kelly | title = An Illustrated Guide to the Protozoa | edition = 2nd | editor-first1 = John J. | editor-last1 = Lee | editor-first2 = Gordon F. | editor-last2 = Leedale | editor-first3 = Phyllis | editor-last3 = Bradbury | publisher = Society of Protozoologists | publication-place = Lawrence, Kansas | date = 2000 | url = https://protistologists.org/publications/illustrated-guide-to-the-protozoa/ | volume = II | pages = 775–782 | chapter-url = https://protistologists.org/wp-content/uploads/2023/07/17SILICOFLAGELLATA.pdf}}</ref>

<ref name="Prego 2023">{{cite journal | last1 = Prego | first1 = Ricardo | first2 = Rafael | last2 = Carballeira | first3 = Yolanda | last3 = Pazos | first4 = Roberto | last4 = Bao | date = 2023 | title = 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? | journal = Toxins | volume = 15 | issue = 7 | pages = 435 | doi = 10.3390/toxins15070435 | pmid = 37505704 | pmc = 10467100 | doi-access = free }}</ref>

<ref name="Stephanocha">{{cite journal|doi=10.11646/phytotaxa.201.3.1 | title = ''Stephanocha nom. nov.'', a replacement name for the illegitimate silicoflagellate genus ''Distephanus'' (Dictyochophyceae) | first1 = Richard | last1 = Jordan | first2 = Kevin |last2 = McCartney | journal = Phytotaxa | volume = 201 | issue = 3 | date = 2015| page = 177 }}</ref>

<ref name="Lee Dictyochophyceae">{{cite book | first = R.E. | last = Lee | chapter = 14. Heterokontophyta: Dictyochophyceae | title = Phycology | chapter-url = https://books.google.com/books?id=gfoIAFHgusgC&pg=PA359 | date = 2008 | publisher = Cambridge University Press | isbn = 978-1-139-46987-6 | pages = 359–364}}</ref>

<ref name="Ling & Takahashi 1985">{{cite journal | title = The silicoflagellate genus ''Octactis'' Schiller 1925: A synonym of the genus ''Distephanus'' | first1 = Hsin Yi | last1 = Ling | first2 = Kozo | last2 = Takahashi | journal = Micropaleontology | volume = 31 | issue = 1 | date = 1985 | pages = 76–81 | doi = 10.2307/1485583 | jstor = 1485583 | bibcode = 1985MiPal..31...76L | url = https://www.jstor.org/stable/1485583 | url-access = subscription }}</ref>

</references>
{{taxonbar|from=Q25367454}}
Category:Ochrophyte genera
Category:Taxa described in 1925

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Adapted from the Wikipedia article [Octactis](https://en.wikipedia.org/wiki/Octactis) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Octactis?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.