THE EUKARYOMONADAE
| SYSTEMATIC BIOLOGY |
THE EUKARYOMONADAE |
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| HOME | SYLLABUS | WEEKLY ASSIGNMENTS | J. SYSTEMATIC BIOLOGY | TAXA OF LIFE | |
| PHYLUM CRYPTOMONADA | |||||
INTRODUCTION TO THE CRYPTOMONADA
Cryptomonada (krip-to-mo-NA-da) is made from two Greek roots that mean hidden (kryptos -κρύφιος) and unit (monada -μονάδα). In this case, the reference is to a cell (a unit) with a hidden gullet, also called a crypt.
The cryptomonads are among the most ubiquitous of aquatic organisms. Their general form is that of a unicell with a subapical gullet from which emerge two unequal flagella. The cell covering is a pellicle made of proteinaceous hexagonal plates. Members of this phylum are about evenly split between autotrophic and heterotrophic taxa. Those that are photosynthetic have at least one chloroplast that has an outer membrane which embraces the large nucleus. All of them have specialized organelles called ejectosomes which line the gullet and occur between the pellicular plates. When deployed, the ejectosomes produce ribbon-like structures that might serve in defense or procuring food.
Cyanomonas (see Figure B) is a cryptomonad that has endosymbiotic cyanobacteria (cyanelles) which function as chloroplasts. They are tiny unicells, but, in large populations, they can have a great impact on local ponds. I witnessed the death of 2,000 catfish in a pond in which a bloom of Cyanomonas occurred. Likely, the cyanelles generated the toxin.
Cryptomonads, though very common, are nearly unknown with regard to life history and other aspects of their biology. Part of the problem is an inability to distinguish species easily because they do not seem to undergo sexual reproduction and the species are both variable and maddeningly similar.
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A. Cryptomonas, a photosynthetic cryptomonad with a pair of laminate chloroplasts. |
B. An illustration of Cyanomonas, an organism with cyanelles rather than chloroplasts. |
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Images taken from: The Systematic Biology Biodiversity Collection |
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SYNOPTIC DESCRIPTION OF THE CRYPTOMONADA
| The description of the phylum comes from Lee (1980), Grell (1976), Kudo (1966), Sze (1986), Lee et al. (1986), Sleigh et al. (1984), Gillott (1990), and Margulis and Schwartz (1988). |
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I. SYNONYMS: Cryptophyta, cryptomonads. II. NUMBER: >200 species. III. PHYLUM CHARACTERISTICS: A. Structure and Physiology: Cell Form: Mainly motile unicells, cell truncate at anterior end; some colonial. Flagella: Two similar flagella, at least one of which bears stiff hairs (mastigonemes); both directed anteriorly. Basal Bodies: Parallel and inserted at the base of the gullet. Cell Covering : Complex covering (= pellicle) of hexagonal proteinaceous plates. Chloroplasts: Extremely variable in color, probably the result of separate endosymbioses; usually with chlorophylls a and c2, carotene, xanthophylls, and phycobillins. Food Reserves: True starch. Mitochondria: Flattened cristae. Golgi: Present. Nucleus: Large, conspicuous and attached to chloroplast outer membrane; cells uninucleate. Centrioles: Absent. Inclusions and Ejectile Organelles: Ribbon-like ejectosomes (trichocysts) in gullet and between pellicular plates. B. Mitosis, Meiosis and Life History Mitosis: Nuclear membrane perforated at the poles; spindle external and penetrates nucleus through polar fenestrae; cytokinesis by longitudinal fission. Meiosis: Not reported. Sexual Reproduction and Life History: Not reported; however, cells often produce asexual cysts and palmelloid stages. C. Ecology: Freshwater and marine; free-living, some endosymbionts; some photosynthetic, phagotrophic, and saprobic. |
SYSTEMATICS OF THE CRYPTOMONADA
Lee (1980), Grell (1976), Kudo (1966), Sze (1986), Lee et al. (1986), Sleigh et al. (1984), Gillott (1990), and Margulis and Schwartz (1988) all agree that the cryptomonads make up a small natural group of taxa. Kudo (1966), Grell (1976) and Lee et al. (1986) lump the cryptomonads into a phylum with most of the flagellated unicells. This system is a modification of Margulis and Schwartz (1988 and 1998) in which the cryptomonad phylum is designated Pr-7 and Pr-11, respectively. Baldauf (2003) presents a consensus view of recent molecular-ultrastructural data in which the cryptomonads occur in a clade with the haptophytes and are associated with the heterokont clade. Until I am convinced that they are part of the heterokont group, I will keep them in the provisional kingdom of the Eukaryomonadae.
HIERARCHICAL CLASSIFICATION OF THE CRYPTOMONADA
| This system is a modification of Margulis and Schwartz (1998) and Gillott (1990). |
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CLASS CRYPTOMONADEA
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This page is maintained by Jack R. Holt-Carlos A. Iudica. Last revised 02/15/2008.
