Diatom A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...

s belong to a large group called the

heterokont Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which ...

s, which include both

autotroph An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...

s such as

golden alga The Chrysophyceae, usually called chrysophytes, chrysomonads, golden-brown algae or golden algae are a large group of algae, found mostly in freshwater. Golden algae is also commonly used to refer to a single species, ''Prymnesium parvum'', which ...

e and

kelp Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underwat ...

; and

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

s such as

water mould Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the resul ...

s. The classification of heterokonts is still unsettled: they may be designated a

division Division or divider may refer to: Mathematics *Division (mathematics), the inverse of multiplication *Division algorithm, a method for computing the result of mathematical division Military *Division (military), a formation typically consisting ...

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

kingdom Kingdom commonly refers to: * A monarchy ruled by a king or queen * Kingdom (biology), a category in biological taxonomy Kingdom may also refer to: Arts and media Television * ''Kingdom'' (British TV series), a 2007 British television drama s ...

, or something intermediate to those. Consequently, diatoms are ranked anywhere from a class, usually called Diatomophyceae or Bacillariophyceae, to a division (=phylum), usually called Bacillariophyta, with corresponding changes in the ranks of their subgroups.

Genera and species

An estimated 20,000

extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...

diatom

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

are believed to exist, of which around 12,000 have been named to date according to Guiry, 2012 (other sources give a wider range of estimatesCanter-Lund, H. and Lund, J.W.G. (1995). ''Freshwater Algae: Their microscopic world explained'', Biopress Limited. .). Around 1,000-1,300 diatom genera have been described, both extant and fossil, of which some 250-300 exist only as fossils.

Classes and orders

Overview

For many years the diatoms—treated either as a class (Bacillariophyceae) or a phylum (Bacillariophyta)—were divided into just 2 orders, corresponding to the centric and the pennate diatoms (

Centrales The Coscinodiscophyceae are a class of diatoms. They are similar to the Centrales, a traditional, paraphyletic subdivision of the heterokont algae known as diatoms. The order is named for the shape of the cell walls (or valves or frustules ...

and

Pennales The order Pennales is a traditional subdivision of the heterokont algae known as diatoms. The order is named for the shape of the cell walls (or valves or frustules) of pennate diatoms, which are elongated in valve view. The valves may be lin ...

; alternative names Biddulphiales and Bacillariales, as used e.g. in Lee, 1989). This classification was extensively overhauled by Round, Crawford and Mann in 1990 who treated the diatoms at a higher rank (division, corresponding to phylum in zoological classification), and promoted the major classification units to classes, maintaining the centric diatoms as a single class

Coscinodiscophyceae The Coscinodiscophyceae are a class of diatoms. They are similar to the Centrales, a traditional, paraphyletic subdivision of the heterokont algae known as diatoms. The order is named for the shape of the cell walls (or valves or frustules) of ...

, but splitting the former pennate diatoms into 2 separate classes,

Fragilariophyceae Fragilariophyceae is a group of pennate diatom The order Pennales is a traditional subdivision of the heterokont algae known as diatoms. The order is named for the shape of the cell walls (or valves or frustules) of pennate diatoms, which a ...

and Bacillariophyceae (the latter older name retained but with an emended definition), between them encompassing 45 orders, the majority of them new. Today (writing at mid 2020) it is recognised that the 1990 system of Round et al. is in need of revision with the advent of newer molecular work, however the best system to replace it is unclear, and current systems in widespread use such as

AlgaeBase AlgaeBase is a global species database of information on all groups of algae, both marine and freshwater, as well as sea-grass. History AlgaeBase began in March 1996, founded by Michael Guiry. Text was copied from this source, which is avai ...

, the

World Register of Marine Species The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive list of names of marine organisms. Content The content of the registry is edited and maintained by scientific specialist ...

and its contributing database DiatomBase, and the system for "all life" represented in Ruggiero et al., 2015, all retain the Round et al. treatment as their basis, albeit with diatoms as a whole treated as a class rather than division/phylum, and Round et al.'s classes reduced to subclasses, for better agreement with the treatment of phylogenetically adjacent groups and their containing taxa. (For references refer the individual sections below). One proposal, by Linda Medlin and co-workers commencing in 2004, is for some of the centric diatom orders considered more closely related to the pennates to be split off as a new class, Mediophyceae, itself more closely aligned with the pennate diatoms than the remaining centrics. This hypothesis—later designated the Coscinodiscophyceae-Mediophyceae-Bacillariophyceae, or Coscinodiscophyceae+(Mediophyceae+Bacillariophyceae) (CMB) hypothesis—has been accepted by D.G. Mann among others, who uses it as the basis for the classification of diatoms as presented in Adl. et al.'s series of syntheses (2005, 2012, 2019), and also in the Bacillariophyta chapter of the 2017 ''Handbook of the Protists'' edited by Archibald et al., with some modifications reflecting the apparent non-monophyly of Medlin et al. original "Coscinodiscophyceae". Meanwhile, a group led by E.C. Theriot favours a different hypothesis of phylogeny, which has been termed the structural gradation hypothesis (SGH) and does not recognise the Mediophyceae as a monophyletic group, while another analysis, that of Parks et al., 2018, finds that the radial centric diatoms (Medlin et al.'s Coscinodiscophyceae) are not monophyletic, but supports the monophyly of Mediophyceae minus ''

Attheya ''Attheya'' is a genus of small single celled diatoms. Some of these species were earlier regarded to belong to ''Chaetoceros'', or to '' Gonioceros'', the taxonomic status of some of these species are still debated.Crawford, R.M., Hinz, F. and K ...

'', which is an anomalous genus. Discussion of the relative merits of these conflicting schemes continues by the various parties involved.

Round et al., 1990

Based on the fact that pennate diatoms either do or do not have a longitudinal groove in the valve, called a ''raphe'', a 1990 classification by Round, Crawford & Mann divides the diatoms (as Bacillarophyta) into three classes, ''centric'' (22 orders); ''pennate without a raphe'' (12 orders); and ''pennate with a raphe'' (11 orders), as follows: Flagilaria

*Phylum Bacillarophyta (diatoms) :*Class

Round & R.M.Crawford (centric diatoms) ::* Subclass Biddulphiophycidae Round & R.M.Crawford :::* Anaulales Round & R.M.Crawford :::* Biddulphiales Krieger :::* Hemiaulales Round & R.M.Crawford :::* Triceratiales Round & R.M.Crawford ::* Subclass Chaetocerotophycidae Round & R.M.Crawford :::* Chaetocerotales Round & R.M.Crawford :::* Leptocylindrales Round & R.M.Crawford ::* Subclass Corethrophycidae Round & R.M.Crawford :::* Corethrales Round & R.M.Crawford ::* Subclass Coscinodiscophycidae Round & R.M.Crawford :::* Arachnoidiscales Round :::* Asterolamprales Round :::*

Aulacoseirales Aulacoseirales is an order of diatoms belonging to the class Bacillariophyceae Bacillariophyceae is a group of pennate diatoms with a raphe (raphids). According to Ruggiero et al., 2015, the diatoms are treated as follows. This treatment larg ...

R.M.Crawford :::* Chrysanthemodiscales Round :::* Coscinodiscales Round :::* Ethmodiscales Round :::* Melosirales R.M.Crawford :::* Orthoseirales R.M.Crawford :::* Paraliales R.M.Crawford :::* Stictocyclales Round :::* Stictodiscales Round & R.M.Crawford ::* Subclass Cymatosirophycidae Round & R.M.Crawford :::*

Cymatosirales Cymatosirales is an order of diatoms in the superorder Cymatosirophycidae Cymatosirophycidae is a group of diatoms in the classe Coscinodiscophyceae The Coscinodiscophyceae are a class of diatoms. They are similar to the Centrales, a trad ...

Round & R.M.Crawford ::* Subclass Lithodesmiophycidae Round & R.M.Crawford :::* Lithodesmiales Round & R.M.Crawford ::* Subclass Rhizosoleniophycidae Round & R.M.Crawford :::* Rhizosoleniales Silva ::* Subclass Thalassiosirophycidae Round & R.M.Crawford :::* Thalassiosirales Glezer & Makarova :* Class

Round (pennate diatoms without a

raphe Raphe (; from Greek ῥαφή, "seam"Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie.'' Oxford: Clarendon Press.) has several diffe ...

(araphids)) ::* Subclass Fragilariophycidae Round :::* Ardissoneales Round :::* Climacospheniales Round :::* Cyclophorales Round & R.M.Crawford :::* Fragilariales P.C.Silva :::* Licmophorales Round :::* Protoraphidales Round :::* Rhabdonematales Round & R.M.Crawford :::* Rhaphoneidales Round :::* Striatellales Round :::* Tabellariales Round :::* Thalassionematales Round :::* Toxariales Round :* Class

Bacillariophyceae Bacillariophyceae is a group of pennate diatoms with a raphe (raphids). According to Ruggiero et al., 2015, the diatoms are treated as follows. This treatment largely reflects that used by Algaebase as at 2015, and is also reflected in the current ...

Haeckel, 1878, ''emend.'' D.G.Mann (pennate diatoms with a raphe (raphids)) ::* Subclass Bacillariophycidae D.G.Mann :::*

Achnanthales Achnanthales is an order of diatoms. References External links * * * Diatom orders {{diatom-stub ...

P.C.Silva :::*

Bacillariales Bacillariaceae is a family of diatoms in the phylum Heterokontophyta, the only family in the order Bacillariales. Some species of genera such as ''Nitzchia'' are found in halophilic environments; for example, in the seasonally flooded Makgadi ...

Hendey :::*

Cymbellales The Cymbellales are a diatom order in the class Bacillariophyceae. They include the following families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other ...

D.G.Mann :::* Dictyoneidales D.G.Mann :::* Lyrellales D.G.Mann :::*

Mastogloiales Mastogloiales is an order of algae belonging to the class Bacillariophyceae Bacillariophyceae is a group of pennate diatoms with a raphe (raphids). According to Ruggiero et al., 2015, the diatoms are treated as follows. This treatment largely ...

D.G.Mann :::* Naviculales Bessey :::* Rhopalodiales D.G.Mann :::* Surirellales D.G.Mann :::* Thalassiophysales D.G.Mann ::* Subclass Eunotiophycidae D.G.Mann :::*

Eunotiales Eunotiales is an order of diatoms, which belongs to Subclass ''Eunotiophycidae'' . References External links ''Eunotiales''at WoRMS Diatom orders {{diatom-stub ...

P.C.Silva

Medlin & Kaczmarska, 2004

An alternate classification for the diatoms based on molecular phylogeny was proposed by Medlin & Kaczmarska in 2004, as follows. Medlin and co-workers erected a new class, Mediophyceae (which could be re-ranked a subclass if diatoms as a whole are ranked as a class rather than a phylum) for the "polar centric" diatoms, which they consider to be more closely related to the pennate rather than to other centric diatoms, a concept which has been followed or further adapted by some (e.g. Adl et al., 2019, see below), but not all subsequent workers at this time. * Phylum Bacillariophyta (diatoms) :* Subphylum Coscinodiscophytina ::* Class

("radial centrics") :::* Arachnoidiscales :::* Asterolamprales :::*

:::* Corethrales :::* Coscinodiscales :::* Chrysanthemodiscales :::* Ethmodiscales :::* Leptocylindrales :::* Melosirales :::* Orthoseirales :::* Rhizosoleniales :::* Stictocyclales :::* Stictodiscales :* Subphylum Bacillariophytina ::* Class Mediophyceae ("polar centrics") :::* Ardissoneales :::* Biddulphiales :::* Chaetocerotales :::*

:::* Hemiaulales :::* Lithodesmiales :::* Thalassiosirales :::* Toxariales :::* Triceratiales ::* Class

(pennate diatoms) :::*

Achnanthales Achnanthales is an order of diatoms. References External links * * * Diatom orders {{diatom-stub ...

:::*

:::* Dictyoneidales :::*

Eunotiales Eunotiales is an order of diatoms, which belongs to Subclass ''Eunotiophycidae'' . References External links ''Eunotiales''at WoRMS Diatom orders {{diatom-stub ...

:::* Fragilariales :::* Licmophorales :::* Lyrellales :::*

:::* Naviculales :::* Rhabdonematales :::* Rhaphoneidales :::* Rhopalodiales :::* Surirellales :::* Tabellariales :::* Thalassionematales :::* Thalassiophysales

Ruggiero et al., 2015

In the treatment for "all life" (down to order, extant taxa only) by Ruggiero et al., 2015, the diatoms are treated as follows. This treatment largely reflects that used by

Algaebase AlgaeBase is a global species database of information on all groups of algae, both marine and freshwater, as well as sea-grass. History AlgaeBase began in March 1996, founded by Michael Guiry. Text was copied from this source, which is avai ...

as at 2015, and is also reflected in the current (mid 2020) treatment used i
DiatomBase
the

(WoRMS) of which DiatomBase is a part, and the

Catalogue of Life The Catalogue of Life is an online database that provides an index of known species of animals, plants, fungi, and microorganisms. It was created in 2001 as a partnership between the global Species 2000 and the American Integrated Taxonomic Info ...

. This treatment is identical to that of Round et al., 1990, except that all diatoms are treated as a single class, Round et al.'s classes are reduced to subclasses, and the latter's original subclasses are omitted. * Superphylum

Heterokonta Heterokonts are a group of protists (formally referred to as Heterokonta, Heterokontae or Heterokontophyta). The group is a major line of eukaryotes. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which a ...

(heterokonts: Ochrophyta plus other phyla)) :* Phylum

Ochrophyta The ochrophytes, subphylum Ochrophytina, is a group of mostly photosynthetic heterokonts. Their plastid is of red algal origin. The classification of the group is still being worked out. Originally, the ochrophytes were regarded as a phylum den ...

(diatoms plus other classes) ::* Class Bacillariophyceae (diatoms) :::* Subclass Bacillariophycidae ::::*

Achnanthales Achnanthales is an order of diatoms. References External links * * * Diatom orders {{diatom-stub ...

::::*

::::* Dictyoneidales ::::*

Eunotiales Eunotiales is an order of diatoms, which belongs to Subclass ''Eunotiophycidae'' . References External links ''Eunotiales''at WoRMS Diatom orders {{diatom-stub ...

::::* Lyrellales ::::*

::::* Naviculales ::::* Rhopalodiales ::::* Surirellales ::::* Thalassiophysales :::* Subclass Coscinodiscophycidae ::::* Anaulales ::::* Arachnoidiscales ::::* Asterolamprales ::::*

::::* Biddulphiales ::::* Chaetocerotales ::::* Chrysanthemodiscales ::::* Corethrales ::::* Coscinodiscales ::::*

::::* Ethmodiscales ::::* Hemiaulales ::::* Leptocylindrales ::::* Lithodesmiales ::::* Melosirales ::::* Orthoseirales ::::* Paraliales ::::* Rhizosoleniales ::::* Stictocyclales ::::* Stictodiscales ::::* Thalassiosirales ::::* Triceratiales :::* Subclass Fragilariophycidae ::::* Ardissoneales ::::* Fragilariophycidae ::::* Climacospheniales ::::* Cyclophorales ::::* Fragilariales ::::* Licmophorales ::::* Protoraphidales ::::* Rhabdonematales ::::* Rhaphoneidales ::::* Striatellales ::::* Tabellariales ::::* Thalassionematales ::::* Toxariales

Adl et al., 2019

Following earlier versions in the treatments of Adl et al. 2005 and 2012, D.G. Mann, in Adl et al. 2019, presented his most recent classification of diatoms as follows, while noting: "This revision reflects numerous advances in the phylogeny of the diatoms over the last decade. Due to our poor taxon sampling outside of the Mediophyceae and pennate diatoms, and the known and anticipated diversity of all diatoms, many clades appear at a high classification level (and the higher level classification is rather flat)." This classification treats diatoms as a phylum (Diatomeae/Bacillariophyta), accepts the class Mediophyceae of Medlin and co-workers, introduces new subphyla and classes for a number of otherwise isolated genera, and re-ranks a number of previously established taxa as subclasses, but does not list orders or families. Inferred ranks have been added for clarity (Adl. et al. do not use ranks, but the intended ones in this portion of the classification are apparent from the choice of endings used, within the system of botanical nomenclature employed). * Clade Diatomista Derelle et al. 2016, emend. Cavalier-Smith 2017 (diatoms plus a subset of other ochrophyte groups) :* Phylum Diatomeae Dumortier 1821 _Bacillariophyta_Haeckel_1878.html" ;"title="Bacillariophyta.html" ;"title=" Bacillariophyta"> Bacillariophyta Haeckel 1878">Bacillariophyta.html" ;"title=" Bacillariophyta"> Bacillariophyta Haeckel 1878(diatoms) ::* Subphylum Leptocylindrophytina D.G. Mann in Adl et al. 2019 :::* Class Leptocylindrophyceae D.G. Mann in Adl et al. 2019 (''Leptocylindrus'', ''Tenuicylindrus'') :::* Class Corethrophyceae D.G. Mann in Adl et al. 2019 (''Corethron'') ::* Subphylum Ellerbeckiophytina D.G. Mann in Adl et al. 2019 ('' Ellerbeckia'') ::* Subphylum Probosciophytina D.G. Mann in Adl et al. 2019 ('' Proboscia'') ::* Subphylum Melosirophytina D.G. Mann in Adl et al. 2019 (''

Aulacoseira ''Aulacoseira'' is a genus of diatoms belonging to the family Aulacoseiraceae Aulacoseirales is an order of diatoms belonging to the class Bacillariophyceae. The order consists only one family: Aulacoseiraceae. Genera Genera: * '' Alveolop ...

'', ''

Melosira ''Melosira'' is a genus of diatoms belonging to the family Melosiraceae. The genus has cosmopolitan distribution, and inhabits both freshwater and marine habitats. Species Species: *'' Gaillonella ampla'' *'' Gaillonella apiculata'' *'' G ...

'', '' Hyalodiscus'', '' Stephanopyxis'', '' Paralia'', '' Endictya'') ::* Subphylum Coscinodiscophytina Medlin & Kaczmarska 2004, emend. ('' Actinoptychus'', ''

Coscinodiscus ''Coscinodiscus'' is a genus of diatoms in the family Coscinodiscaceae Coscinodiscaceae is a diatom family in the order Coscinodiscales. References External links Diatom families Coscinodiscophyceae Taxa named by Friedrich Traugott Küt ...

'', ''

Actinocyclus ''Actinocyclus'' is a genus of sea slugs, dorid nudibranchs, shell-less marine (ocean), marine gastropod molluscs in the family Actinocyclidae,Rosenberg, G. (2012). ''Actinocyclus'' Ehrenberg, 1831. Accessed through: World Register of Marine Sp ...

'', '' Asteromphalus'', '' Aulacodiscus'', '' Stellarima'') ::* Subphylum Rhizosoleniophytina D.G. Mann in Adl et al. 2019 (''

Guinardia ''Guinardia'' is a genus of diatoms belonging to the family Rhizosoleniaceae. The genus was first described by H. Peragallo in 1892. The genus has cosmopolitan distribution. Species: * '' Guinardia delicatula'' * '' Guinardia flaccida'' * ...

'', '' Rhizosolenia'', '' Pseudosolenia'') ::* Subphylum Arachnoidiscophytina D.G. Mann in Adl et al. 2019 ('' Arachnoidiscus'') ::* Subphylum Bacillariophytina Medlin & Kaczmarska 2004, emend. :::* Class Mediophyceae Jouse & Proshkina-Lavrenko in Medlin & Kaczmarska 2004 ::::* Subclass Chaetocerotophycidae Round & R.M. Crawford in Round et al. 1990, emend. ::::* Subclass Lithodesmiophycidae Round & R.M. Crawford in Round et al. 1990, emend. ::::* Subclass Thalassiosirophycidae Round & R.M. Crawford in Round et al. 1990 ::::* Subclass Cymatosirophycidae Round & R.M. Crawford in Round et al. 1990 ::::* Subclass Odontellophycidae D.G. Mann in Adl et al. 2019 ::::* Subclass Chrysanthemodiscophycidae D.G. Mann in Adl et al. 2019 :::* Class Biddulphiophyceae D.G. Mann in Adl et al. 2019 ::::* Subclass Biddulphiophycidae Round and R.M. Crawford in Round et al. 1990, emend. ::::* Biddulphiophyceae incertae sedis (''

'') :::* Class

Haeckel 1878, emend. ::::* Bacillariophyceae incertae sedis (Striatellaceae) ::::* Subclass Urneidophycidae Medlin 2016 ::::* Subclass Fragilariophycidae Round in Round, Crawford & Mann 1990, emend. ::::* Subclass Bacillariophycidae D.G. Mann in Round, Crawford & Mann 1990, emend.

Others

Another systematic approach to classification was proposed in 1995, the Hoek, Mann and Jahns system. Previous versions of the Adl et al., 2019 classification appeared in Adl et al. 2005 and Adl et al. 2012, also in the chapter "Bacillariophyta" by Mann, Crawford & Round in the 2017 ''Handbook of the Protists'' edited by Archibald et al., in which some groups later named as formal taxa are listed under informal names (leptocylindrids, corethrids, melosirids, etc.).

References

{{reflist Diatoms SAR supergroup taxonomy