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Pedinellales ( ICN) or Pedinellida (
ICZN The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its formal author, t ...
) is a group of single-celled
algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
found in both marine environments and freshwater. These are found in both freshwater and marine environments, and most genera are sessile, attached by posterior stalks. The flagellum is at the anterior of the cell, and the tentacles surround it, often capturing small prey drawn in by its current. The colored genera are '' Pedinella'', '' Apedinella'', '' Pseudopedinella'', and '' Mesopedinella''. Several more genera have lost their chloroplasts and feed entirely by
phagocytosis Phagocytosis () is the process by which a cell (biology), cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs ph ...
. These are '' Parapedinella'', '' Actinomonas'', and '' Pteridomonas''. It also appears that certain
heliozoa Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (Pseudopodia#Morphology, axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule- ...
are actually derived pedinellids. ''Ciliophrys'' alternates between a mobile flagellate stage and a heliozoan feeding stage, where the body is contracted with extended axopods all over its surface, and the flagellum is curled up into a tight figure eight. The actinophryids, ''Actinophrys'' and ''Actinosphaerium'', exist only in a heliozoan form with no flagellum and with more elaborate bundles of microtubules supporting their axopods. Their inclusion was argued by Mikrjukov and Patterson, who coined the term actinodine to refer specifically to this extended group. Pedinellids were classified as
heliozoa Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (Pseudopodia#Morphology, axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule- ...
ns by some authors. The colored pedinellids were originally treated as a family of
golden algae 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'', wh ...
in the order Ochromonadales, promoted to an order Pedinellales by Zimmerman in 1984. Their relationship to the silicoflagellates became apparent some time later, and Patterson defined this rankless group for the two in 1994. Moestrup treated it as the class Dictyochophyceae, previously restricted to the silicoflagellates, while Cavalier-Smith defined a new class Actinochrysophyceae for them.


Systematics


Taxonomic history

Pedinellids have been known since the 19th century, but were classified as either
algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
or
heliozoa Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (Pseudopodia#Morphology, axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule- ...
n
protozoa Protozoa (: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically ...
due to the absence of
chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...
s in some species. Before the taxonomic revisions that took place in the late 20th century, pedinellids were treated as a single
family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Pedinellaceae, described in 1910 by Pascher. Some authors classified pedinellids within the
order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...
Ochromonadales Ochromonadales is an order of single-celled algae belonging to the class Chrysophyceae, also known as golden algae. Initially it contained numerous groups of flagellates that were not closely related. During the late 20th century, advancements i ...
, together with a variety of unrelated
heterokont The stramenopiles, also called heterokonts, are protists 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, an ...
s such as
Synuraceae ''Synura'' is a genus of colonial chrysomonad algae covered with silica scales. It is the most conspicuous genus of the order Synurales. Description Species of ''Synura'' form microscopic, spherical colonies, composed of multiple cells attache ...
and Bicosoecaceae, as part of the class
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'', wh ...
or golden algae. In 1985, phycologists Birthe Zimmermann, Øjvind Moestrup and Guy Hällfors classified them as an independent order, Pedinellales. The same year, John J. Lee and coauthors segregated the phagotrophic (i.e. without chloroplasts) pedinellids as a different order Ciliophryida under the
polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...
class Heliozoea. Other authors, such as
Thomas Cavalier-Smith Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford. His research has led to discov ...
, went a step further and proposed treating pedinellids as a separate class, under the name of Pedinellea (spelt Pedinellophyceae under botanical nomenclature). In 1995, Charles J. O'Kelly and Daniel E. Wujek classified the Dictyochophyceae in three orders: Rhizochromulinales (containing the sole genus '' Rhizochromulina''), Pedinellales (containing all pedinellids) and Dictyochales (
silicoflagellate The silicoflagellates (order Dictyochales) 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 a ...
s), separating them from golden algae. Simultaneously, Cavalier-Smith proposed a slightly different classification where he created a new class Actinochrysea to embrace these three groups, avoiding the usage of Dictyochophyceae as a name. He considered pedinellids as subclass Pedinellidae, with two orders: Pedinellales (with chloroplasts), containing the families Pedinellaceae and Apedinellaceae; and Ciliophryales (without chloroplasts), containing Actinomonadaceae and Ciliophryaceae. The remaining two groups, Rhizochromulinales and Dictyochales, were transferred to a separate subclass Dictyochidae. The next year, Cavalier-Smith and Ema E. Chao recognized that the chloroplast losses were
polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...
, and the family Actinomonadaceae was transferred to Pedinellales on the basis of a
molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...
analysis. In 2006, Cavalier-Smith once again rearranged the classification. He lowered Actinochrysea to a subclass Actinochrysia within a new class Hypogyristea, which also included pelagophytes as subclass Pelagophycia. He lumped together all pedinellid genera in the family Actinomonadaceae and new suborder Actinomonadineae, with the exception of ''Ciliophrys'', which he included with the non-pedinellid ''Rhizochromulina'' in two families of a new suborder Ciliophryineae. He maintained this classification in later years. In 2018, he finally recognized class Dictyochophyceae, and created the subclass Pedinellia or Pedinellophycidae (equivalent to his earlier Actinochrysea/Actinochrysia) to lump together pedinellids and silicoflagellates. Pelagophytes remained under the subclass Pelagophycidae, and two genera of more uncertain placement under a third subclass Sulcophycidae: '' Olisthodiscus'' and '' Sulcochrysis''. Cavalier-Smith's taxonomic scheme is not accepted by the scientific community. Instead, Moestrup's 1995 classification is more commonly supported, where pedinellids are all contained in the order Pedinellales, rendering Ciliophryales a
junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...
. They are considered part of Dictyochophyceae, along with orders Dictyochales (silicoflagellates), Rhizochromulinales (''Rhizochromulina''), and a more recent fourth order Florenciellales. In addition, pelagophytes are rejected as members of Dictyochophyceae, and instead form an independent class Pelagophyceae. Within pedinellids, there have been several attempts to establish different families according to morphological data such as the presence or absence of stalks and chloroplasts. However, molecular analyses do not support these internal divisions. Consequently, all pedinellids have been grouped into a single family, Actinomonadaceae, which has taxonomic preference due to being the earliest described, and all other proposed families (Pedinellaceae, Apedinellaceae, etc.) have become junior synonyms.


Classification

Pedinellids currently sum the following genera: * '' Cyrtophora'' Strand 1929 * '' Palatinella'' Lauterborn 1906 * '' Actinomonas'' Kent 1880 * '' Apedinella'' Throndsen 1971 * '' Ciliophrys'' Cienkowski 1876 * '' Helicopedinella'' Sekiguchi et al. 2003 * '' Mesopedinella'' Daugbjerg 1996 * '' Parapedinella'' Pedersen, Beech & Thomsen 1986 * '' Pedinella'' Wyssotzki 1887 non Dahl 1909 * '' Pseudopedinella'' Carter 1937 * '' Pteridomonas'' Penard 1889


References


External links

* * {{Authority control Ochrophyte orders Dictyochophyceae Taxa described in 1880