Overview
The euglenids (or euglenoids) are one of the best-known groups of , commonly found in freshwater especially when it is rich in organic materials, with a few marine and endosymbiotic members. Many euglenids have chloroplasts and produce energy through photosynthesis, but others feed by phagocytosis or strictly by diffusion. They belong to the phylum Euglenophyta, and their cell structure is typical of that group.
Euglenids are distinguished mainly by the presence of a pellicle, which is composed of proteinaceous strips underneath the cell membrane, supported by dorsal and ventral microtubules. This varies from rigid to flexible, and gives the cell its shape, often giving it distinctive striations. In many euglenids the strips can slide past one another, causing an inching motion called metaboly. Otherwise they move using the flagella.
The euglenids were first defined by Otto Bütschli in 1884 as the flagellate order Euglenida. Botanists subsequently treated the algal division Euglenophyta; thus they were classified as both animals and plants, as they share characteristics with both. This conflict is an example of why the kingdom Protista was adopted. However, they retained their double-placement until the flagellates were split up, and both names are still used to refer to the group.
Classification & Nutrition
The classification of euglenids is still variable, as groups are being revised to conform with their molecular phylogeny. To some extent, however, the results support the traditional groups based on differences in nutrition and number of flagella; at any rate these provide a starting point for considering euglenid diversity.
As with other Euglenozoa, the primitive mode of nutrition is phagocytosis. Prey such as bacteria and smaller flagellates are ingested through a cytostome, supported by microtubules. These are often packed together to form two or more rods, which function in ingestion, and in Entosiphon form an extendable siphon. Most phagotrophic euglenids have two flagella, one leading and one trailing. The latter is used for gliding along the substrate. In some, such as Peranema, the leading flagellum is rigid and beats only at its tip.
Osmotrophic Euglenids
In many cases exposure to certain chemicals or prolonged absence of light may kill off the chloroplasts without otherwise harming the organism. There are a number of species where chloroplasts are absent, formerly treated in separate genera such as Astasia (colorless Euglena) and Hyalophacus (colorless Phacus). Since they lack a developed cytostome, these forms feed exclusively by absorption.
Taxonomy
The Family Euglenaceae is further organized into finer groupings including:
- Genus (16): Amblyophis · Astasia · Calkinsia · Cryptoglena · Euglena · Euglenopsis · Eutreptia · Lagenella · Lagenula · Lepocinclis · Menoidium · Monomorphina · Parmidium · Phacus · Strombomonas · Trachelomonas
- Species: ZipcodeZoo has pages for 1,500 species and subspecies in the Family Euglenaceae.
Genera
Amblyophis
Astasia
Astasis (also known as astasia) is the inability to stand because of disruption of muscle coordination. The condition is caused by injury to the . It is frequently, though not invariably accompanied by abasia, an inability to walk. [more]
Calkinsia
Cryptoglena
Euglena
Euglena are a common group of protists, of the class Euglenoidea of the phylum Euglenophyta. Currently, over 1000 species of Euglena have been described. Marin et al. (2003) revised the genus so and including several species without chloroplasts, formerly classified as Astasia and Khawkinea. Euglena sometimes can be considered to have both plant and animal features. [more]
Euglenopsis
Eutreptia
Lagenella
Lagenula
Lepocinclis
Menoidium
Monomorphina
Parmidium
Phacus
Strombomonas
Trachelomonas
The genus Trachelomonas is characterized by the presence of a shell-like covering called a lorica. Details of lorica structure determine the classification of distinct species in the genus. The lorica can exist in spherical, elliptical, cylindrical, and pyriform (pear-shaped) forms and measures anywhere from 5 to 100 µ in diameter or length. The lorica surface can be smooth, punctuate or striate and range from hyaline, to yellow, or brown. These colors are due to the accumulation of ferric hydroxide and manganic oxide deposited with the mucilage and minerals that comprise the lorica. In Trachelomonas, the presence of a lorica obscures cytoplasmic details of the underlying cell. In each Trachelomonas cell, there is a gap at the apex of the lorica from which the flagellum protrudes. Thickening around this gap results in a rim-like or collar-like appearance. During asexual reproduction, the nucleus divides yielding two daughter cells one of which exits through the opening in the lorica. This new cell then synthesizes its own new lorica. [more]
At least 681 species and subspecies belong to the Genus Trachelomonas.
More info about the Genus Trachelomonas may be found here.
References
- ^ lee, R.E. (2008). Phycology, 4th edition. Cambridge University Press. ISBN 978-0521638838.
Sources
- The text on this page is licensed under the GNU Free Documentation License. It includes material from Wikipedia retrieved Friday, November 14, 2008.
- The distribution map on the Distribution tab comes from the Global Biodiversity Information Facility and is used with permission.
- Photographs on this page are copyrighted by individual photographers, and individual copyrights apply.
- The technology underlying this page, including the controls behind Keep Exploring, is owned by the BayScience Foundation. All rights are reserved.