Wikipedia 10K Redux by Reagle from Starling archive. Bugs abound!!!

<-- Previous | Newer --> | Current: 984214576 Josh Grosse at Sat, 10 Mar 2001 08:56:16 +0000.

Euglenids

The euglenids (Euglenophyta, Euglenida) are one of the best-known groups of [[flagellate]]s, and belong to the [[Euglenozoa]].  They are distinguished by a number of features, most notably the storage of food as the [[carbohydrate]] [[paramylon]], and the presence of a series of microtubule-supported proteinaceous strips underneath the cell membrane that form a ''pellicle'' that gives the cell its shape.  This varies from rigid to flexible, in the latter case allowing the cell to perform an inching motion called ''metaboly''.

Many euglenids are primitively colorless and feed on bacteria and smaller flagellates.  More needs to be said about these.  One neat thing is that many, for instance ''Peranema'', swim with the anterior flagellum held rigid, beating only at the tip.

At some point, euglenids aquired chloroplasts.  These are typically bound by three cell membranes, so presumably they were retained from some ingested [[alga]], with the outermost membrane corrseponding to a normal [[vacuole]].  As far as pigmentation is concerned, the chloroplasts contain only chlorophyll a.  Photosynthetic euglenids have generally lost the cytostome but are still capable of feeding heterotrophically, and in fact the chloroplasts can be killed off without damaging the host cell.  A few genera of euglenids are secondarily colorless - ''[[Astasia]]'' and ''Khawakinea'', which properly belong within ''[[Euglena]]'', and ''Hyalophacus'', which properly belongs within ''[[Phacus]]''.

Colored euglenids do not generally have the leading-trailing biflagellate pattern found in the primitively colorless forms and most other euglenozoa.  In [[Euglena]], [[Phacus]], and their kin, the trailing flagellum is shortened so that it does not even leave the flagellar pocket, making the organisms effectively monoflagellate; in [[Eutreptia]] the two flagella are roughly equal in length and function.  In these forms the flagella tend to undergo a looping motion, pulling the cell through the water in a slightly-helical path.

Most colored euglenids have an ''stigma'', or eyespot (lost in secondarily colorless forms), which is a small splotch of red pigmentation shading the flagellar pocket.  At the base of the leading flagellum is a collection of light sensitive crystals, so together the two act as a sort of directional eye.  This is in fact where the group's name comes from: [[Greek language/Lexicon|Gr]] ''eu''+''glĂȘne'', eyeball.

A few euglenids, eg ''Trachelomonas'', live encased within a rigid lorica, which is sometimes attached to the substrate; unlike a cell wall this can easily be broken without harming the cell.  There is one form, ''Colacium'', that is aflagellate and non-motile in its adult stage, forming branched colonies held together by mucilage, but other than this no euglenids have made any move towards the sort of complex organization found in other algae.