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granules composed primarily of iron (Dodge, 1975; Leedale, 1975; Walne, 1980; West and Walne, 1980; West et al., 1980).

Pellicular ornamentation occurs in a number of euglenoids, particularly in species of Phacus (Figs. 6.4, 6.14(e)) and in the Euglena spirogyra complex. The process is related to envelope formation in Trachelomonas (Figs. 6.12, 6.14(d)) and stalk formation in Colacium (Figs. 6.15, 6.16).

Chloroplasts and storage products

Euglenoid chloroplasts arose from a secondary endosymbiosis. The chloroplasts originated from the chloroplasts of a scaly flagellate in the green algal class Prasinophyceae (Marin, 2004). The euglenoid chloroplasts are surrounded by two membranes of the chloroplast envelope plus one membrane of chloroplast endoplasmic reticulum; the latter membrane is not continuous with the nuclear membrane (Figs. 6.2, 6.3, 6.14). The chloroplasts are usually discoid or plate-like with a central pyrenoid. The thylakoids are grouped into bands of three, with two thylakoid bands traversing the pyrenoid.

A shield of paramylon grains surrounds the pyrenoid, but outside the chloroplast, in phototropically grown cells (Figs. 6.2, 6.3, 6.14). Paramylon granules are distributed throughout the cytoplasm in heterotrophically grown cells in the dark (Bäumer et al., 2001). Gottlieb isolated the granules in 1850, and showed that they were composed of a carbohydrate that although isomeric with starch (amylon), was not stained with iodine. For this reason, they were termed paramylon granules. They have since been shown to be composed of a -1,3 linked glucan (Barsanti et al., 2001). The paramylon granule is a membranebounded crystal composed of two types of segments – rectangular solids and wedges (Kiss et al., 1987). The liquid storage product, chrysolaminarin, can be an alternative storage product in some Euglenophyceae such as Eutreptiella gymnastica (Fig. 6.11) and Sphenomonas laevis where it can occur with solid paramylon grains in the same cell (Leedale, 1967; Throndsen, 1969). Whereas the paramylon usually occurs as a shield of grains, the chrysolaminarin occurs in vacuoles

primarily in the anterior part of the cell (Throndsen, 1973).

Nutrition

The Euglenophyceae have a number of modes of nutrition, depending on the species involved. No euglenoid has yet been demonstrated to be fully photoautotrophic – capable of living on a medium devoid of all organic compounds (including vitamins), with carbon dioxide as a carbon source, nitrates or ammonium salts as a nitrogen source, and light as an energy source. All green euglenoid flagellates so far studied are photoauxotrophic – capable of growing in a medium devoid of organic nutrients, with carbon dioxide, ammonium salts, and light, but needing at least one vitamin. Euglena gracilis has an absolute requirement for vitamin B12 (Hutner and Provasoli, 1955), it having been calculated that between 4900 and 22 000 molecules of vitamin B12 are necessary for cell division (Carell, 1969). Vitamin B12-starved cells increase in cell volume, sometimes to 10 times the size of control organisms, the cells in the final stage of vitamin B12 starvation often being polylobed, polynucleate, and containing more than the normal number of chloroplasts per cell (Bertaux and Valencia, 1971, 1973; Carell, 1969). During vitamin B12 starvation, total cellular RNA and protein increase 400% to 500% compared with controls (Carell et al., 1970). The chloroplast number per cell increases during this period, although the ratio of chloroplast protein to total cellular protein remains constant, evidence for the independence of chloroplast division from nuclear division (Bré and Lefort-Tran, 1974). Although the protein increase is 400% to 500% during vitamin B12 starvation, the total DNA increases only about 180%, suggesting that a particular step in DNA replication may be preferentially affected by the vitamin (Bré et al., 1975).

As Euglena cells age, they become immobile and spherical, with a tendency to form enlarged “giant” cells and to accumulate orange to black pigment bodies. Aging also results in the formation of larger numbers of lysosomes and microbodies with an increase in the degradation of organelles (Gomez et al., 1974). The older cells