Euglenaceae (also known as Euglenidae) is a family of

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and the ...

s in the phylum

Euglenozoa Euglenozoa are a large group of flagellate Discoba. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. Euglenozoa are represented by four major groups, ''i.e.,'' Kinetoplastea, ...

. The family includes the most well-known euglenoid genus, ''

Euglena ''Euglena'' is a genus of Unicellular organism, single-celled, flagellate eukaryotes. It is the best-known and most widely studied member of the class Euglenoidea, a diverse group containing some 54 genera and at least 200 species. Species of '' ...

''.

Nomenclature

The family Euglenaceae is also known by the name Euglenidae. The origin of this dual naming system is because of the history of protists. Euglenids have been treated as both

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 ...

and

protozoan 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 ...

s, which are governed by separate

nomenclature codes Nomenclature codes or codes of nomenclature are the various rulebooks that govern the naming of living organisms. Standardizing the scientific names of biological organisms allows researchers to discuss findings (including the discovery of new s ...

. If treated as an alga, it would fall under the

International Code of Nomenclature for algae, fungi, and plants The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN or ICNafp) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all tho ...

(ICN) and its correct name would be Euglenaceae; if treated under the

International Code of Zoological Nomenclature The International Code of Zoological Nomenclature (ICZN) is a widely accepted Convention (norm), convention in zoology that rules the formal scientific name, scientific naming of organisms treated as animals. It is also informally known as the I ...

(ICZN) it is called Euglenidae. Euglenids such as these are considered to be ambiregnal protists due to their parallel naming systems.

Morphology

Euglenaceae show the most morphological diversity within the class Euglenophyceae. They are mostly single-celled organisms, except for the genus '' Colacium''. They are free-living or sometimes inhabiting the digestive tracts of animals. Two genera, '' Strombomonas'' and '' Trachelomonas'' produce outer shells called loricae. As with other euglenids, cells in the Euglenaceae are surrounded by a series of proteinaceous strips called the pellicle; the pellicle can stretch in most genera, allowing the cell to contract, creating a type of movement called metaboly. The genus '' Monomorphina'' is rigid or slightly metabolic.

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 are present in most species, except for a few species that have lost them.

s are diverse in this family, with the size, shape, number, and presence of

pyrenoid Pyrenoids are sub-cellular phase-separated micro-compartments found in chloroplasts of many algae,Giordano, M., Beardall, J., & Raven, J. A. (2005). CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. ''An ...

s being important identifying characteristics.

Phylogeny

In its current

circumscription Circumscription may refer to: * Circumscribed circle * Circumscription (logic) *Circumscription (taxonomy) * Circumscription theory, a theory about the origins of the political state in the history of human evolution proposed by the American anthr ...

, Euglenaceae is

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

. Its sister family is Phacaceae, which contains several genera ('' Lepocinclis'', '' Phacus'', and '' Discoplastis'') formerly included within Euglenaceae. Two phylogenies are shown below.

Kim et al. (2010)

In this phylogeny, most ''Euglena'' species are sister to a clade consisting of ''Euglenaria'' and ''Euglena archaeoplastidiata''.

Bicudo & Menezes (2016)

This phylogeny places ''Euglena'' as sister to all other genera in Euglenaceae except for the genus ''Euglenaformis''.

References

{{Authority control Euglenozoa Euglenozoa families