THE CERCOZOAE
| SYSTEMATIC BIOLOGY |
THE CERCOZOAE |
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| HOME | SYLLABUS | WEEKLY ASSIGNMENTS | J. SYSTEMATIC BIOLOGY | TAXA OF LIFE | |
| PHYLUM CHLORARACHNIOPHYTA | |||||
INTRODUCTION TO THE CHLORARACHNIOPHYTA
Chlorarachniophyta (klor-a-rak-ni-O-fa-ta) is derived from three Greek roots that mean green (chloros -χλοερός); spider (arachne -αράχνη); and plant (phyto -φυτό). The reference is to green, spider web appearance of the cellular colonies.
The chlorarachniophytes are filose green amoebae that link together in a net-like web, forming a large confluent cellular mass with many nuclei (a plasmodium). They occur only in marine environments where they are associated with siphonous green algae. The individual cell bodies have about four bi-lobed chloroplasts each. In addition, each chloroplast has a degenerate nucleus, a nucleomorph, which is bound within membranes of the chloroplast. This is some of the best evidence that some eukaryotes (perhaps most different types) became photosynthetic by entering into a endosymbiotic relationship with another eukaryote. Because the chloroplast stores photosynthate as paramylon and uses chlorophylls a and b, it is likely that the enslaved eukaryote was a euglenoid. This is called secondary endosymbiosis, a condition that occurs also in the cryptomonads. Individual examples have been found in the dinoflagellates and some other taxa.
The filose amoebae can release uniflagellate swarmer cells, each of which has a single, posteriorly-directed flagellum that is inserted antapically and winds down the cell in a groove. Whether these also function as gametes is not known.
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A. A DIC image of Chlorarachnion that shows the characteristic filopodia and chloroplasts. |
| Image taken from: http://microscope.mbl.edu/baypaul/microscope/images/t_imgAZ/chlorarachnion_bgw.jpg |
SYNOPTIC DESCRIPTION OF THE CHLORARACHNIOPHYTA
| The description of the phylum comes from Hibberd (1990), Patterson (1999), van den Hoek et al. (1995). |
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I. SYNONYMS: chlorarachniophytes, amoebae. II. NUMBER: 6 species. III. PHYLUM CHARACTERISTICS A. Structure and Physiology Cell Form: Filose amoebae that join in a web. They can form cysts and motile zoospores. Flagella: Zoospores with a single posteriorly-directed whiplash flagellum; inserted laterally. Basal Bodies: Two, one barren and with microtubular roots. Cell Covering: Naked; cyst covering unknown. Chloroplasts: Present within membranes of the endosymbiont. Chlorophylls a and b. One pyrenoid and 1-3 thylakoids. Food Reserves: Paramylon. Mitochondria: Tubular cristae. Nucleus: Uninucleate. Centrioles: ? Inclusions and ejectile organelles: Not present. B. Mitosis, Meiosis and Life History Mitosis: Presumed closed with an internal spindle. Meiosis: ? Sexual reproduction and life history: Life history involves the production of flagellated zoospores that may be facultative gametes. They may form cysts in which tetrads of cells (meiosis?) are produced and can give rise to the uniflagellate swarmers (gametes?). By and large, reproduction is vegetative. C. Ecology: Free-living marine amoebae associated with marine coenocytic (siphonous) green algae.. |
SYSTEMATICS OF THE CHLORARACHNIOPHYTA
Geitler (1930) placed them in the Xanthophyta after their discovery. Later, Hibberd and Norris (1984) and Hibberd (1990) moved them to a phylum all to their own. Despite that, Margulis and Schwartz (1999) retained them in the Rhizopoda. Evidence since then clearly associates them with other filose amoebae in the Rhizaria (Bhattacharya et al. 1995; and McFadden et al. 1997). Archibald and Keeling (2004) examined actin and ubiquitin gene sequences and found that the chlorarachniophytes were sisters to the foraminifera+plasmodiophora clade within the cercozoans.
HIERARCHICAL CLASSIFICATION OF THE CHLORARACHNIOPHYTA
| TAXONOMY OF THE PHYLUM CHLORARACHNIOPHYTA. This system is a modification of Hibberd (1990). |
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CLASS CHLORARACHNIOPHYTEA
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This page is maintained by Jack R. Holt. Last revised: 03/14/2008.
