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Euglenophyta (euglenoids)



Euglena spp. (above) and Phacus (right), two main clades of euglenoids.

Supergroup: Uncertainly affiliated with the Excavates.

On-line sources

The Euglenoid Project

Independent studies in Poland and the US recently showed that there are two major clades within Euglenoids, one containing Phacus and Lepocinclis, the other with Euglena, Trachelomonas, etc.  [References: Milanowski et al. 2006,  J. Phycol. 42: 721-730; Triemer et al. 2006, J. Phycol. 42: 731-740.]

Characteristics of the Division

(After van den Hoek et al.)

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1. The organisms in this very distinctive phylum, with a  characteristic morphological and ultrastructural identity, are mostly unicellular flagellates. They are in a different Supergroup from all other photosynthetic organisms. Most are freshwater, a few are marine. Some are photosynthetic but many are not; 

photosynthetic ones can bleach (lose their pigment) and feed heterotrophically.

2. The cells do not have walls but are protected by a pellicle, which lies within the cytoplasm. This is composed of  strips of protein, which spiral around the cell from one end to the other. The cells often change shape as they move around ("euglenoid movement" -- see video clips on the Euglenoid Project website).

3. The flagella arise from the bottom of a flask-shaped invagination consisting of a canal and a reservoir. There are almost always two flagella, but one of these is often very short.

4. The chloroplasts contain chlorophylls a and b; chlorophyll c is absent and the accessory pigments do not mask the chlorophylls.

5. Within the chloroplasts, the thylakoids are usually grouped into threes, as  in the Heterokontophyta and Dinophyta, but there is no girdle lamella.

6. An orange-red eyespot is free in the cytoplasm (not in the chloroplast) and consists of a number of droplets containing carotenoids. The eyespot lies under the plasmalemma by the reservoir; near it the long flagellum bears a swelling.

7. The reserve polysaccharide is paramylon, a β 1,3-linked glucan. This lies in the cytoplasm in the form of granules, which are often ring-like. Pyrenoids may be present.

8. At the anterior end of the cell is a large contractile vacuole, which discharges into the reservoir.

 

C. Lobban. 8/30/06