The Parmales are an order of marine microalgae within the

Bolidophyceae Bolidophyceae is a class of photosynthetic heterokont picophytoplankton, and consist of less than 20 known species. They are distinguished by the angle of flagellar insertion and swimming patterns as well as recent molecular analyses. Bolidophyc ...

class. They are found worldwide and characterized by a cell wall composed of 5-8 interlocking silica plates with distinct forms. They were initially thought to be loricate choanoflagellates but were shown to be a separate phyla entirely upon the discovery of chloroplasts, placing it among the photosynthetic

stramenopiles Stramenopile is a clade of organisms distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella, in some they are attached to other areas of the cellular surface, and in some they have be ...

. The group is divided into two distinct morphologies- the naked and mobile bolidophyte form and the non-mobile and silica-plate covered parmalean form. The bolidophyte form lacks silica plates and has two unequal flagella inserted ventrally, vaguely reminiscent of '' Chlamydomonas''. The parmalean form is similar to the diatoms as it is coated in silicate plates. These silicate plates are used to divide the Parmales into separate genera based upon the number and location of the siliceous plates. Unlike the diatoms, the Parmales are able to grow in silica-limiting environments because the synthesis of the silica plates is not directly connected to growth or reproduction. The Parmales actively feed on nanophytoplankton such as ''

Prochlorococcus ''Prochlorococcus'' is a genus of very small (0.6 μm) marine cyanobacteria with an unusual pigmentation ( chlorophyll ''a2'' and ''b2''). These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynth ...

'' and ''

Synechococcus ''Synechococcus'' (from the Greek ''synechos'', in succession, and the Greek ''kokkos'', granule) is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 to 1.5 µm. The photosynthetic c ...

'' and are one of the most important grazers on these cyanobacteria in oligotrophic waters. This heterotrophy serves as an important step in the foundation of the

microbial loop The microbial loop describes a trophic pathway where, in aquatic systems, dissolved organic carbon (DOC) is returned to higher trophic levels via its incorporation into bacterial biomass, and then coupled with the classic food chain formed by phy ...

Etymology

The name comes from th
Latin word
for a small, round shield carried by infantry and cavalry. It refers to the silica plates that the Parmales are covered by.

Distribution

Parmales can be found in all the major world oceans. However, their density is consistently low (10-100 cells/ml) and they represent at most 3% of the phytoplankton present. They are most abundant in polar and subarctic waters but are also capable of growing in tropical and subtropical locations. Within the water column, Parmales are found in the upper, euphotic portion where they remain without difficulty due to their small size. It is currently unknown whether they have mechanisms to regulate buoyancy. Parmales have also been found as fossils in the Middle America Trench in sediments from the mid to late

Quaternary period The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

. Older fossils have been reported but are unverifiable.

Taxonomy

Although initially placed within the

Chrysophyceae 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'', whic ...

, Parmales were shown in 2016 to belong to the

* Class Bolidophyceae Guillou & Chretiennot-Dinet 1999 ** Order Parmales Booth & Marchant 1987 *** Family Pentalaminaceae Marchant 1987 **** Genus '' Pentalamina'' Marchant 1987 ***** Species '' Pentalamina corona'' Marchant 1987 *** Family Triparmaceae Booth & Marchant 1988 **** Genus '' Tetraparma'' Booth 1987 ***** Species '' T. catinifera'' ***** Species '' T. gracilis'' ***** Species '' T. insecta'' Bravo-Sierra & Hernández-Becerril 2003 ***** Species '' T. pelagica'' Booth & Marchant 1987 ***** Species '' T. silverae'' Fujita & Jordan 2017 ***** Species '' T. trullifera'' Fujita & Jordan 2017 **** Genus '' Triparma'' Booth & Marchant 1987 ***** Species '' T. columacea'' Booth 1987 ***** Species '' T. eleuthera'' Ichinomiya & Lopes dos Santos 2016 ***** Species '' T. laevis'' Booth 1987 ***** Species '' T. mediterranea'' (Guillou & Chrétiennot-Dinet) Ichinomiya & Lopes dos Santos 2016 ***** Species '' T. pacifica'' (Guillou & Chrétiennot-Dinet) Ichinomiya & Lopes dos Santos 2016 ***** Species '' T. retinervis'' Booth 1987 ***** Species '' T. strigata'' Booth 1987 ***** Species '' T. verrucosa'' Booth 1987

References

{{Taxonbar, from=Q21221606 Ochrophyta Heterokont orders