ALVEOLATAE

Dinoflagellata (di-no-fla-ghe-LA-ta) is made of two roots, one Greek and one Latin that mean eddy, as in spinning water (din-e -δίνη); and whip (flagellum). The reference is to motile cells that spin as they swim.

The dinoflagellates produce distinctive motile cells that are divided into an anterior (epitheca) and a posterior (hypotheca), separated by a groove called the cingulum (Figure A). The motile cells have two flagella inserted in the center of the ventral portion of the cell. It is encircled by a ribbon-like flagellum that lies in the cingulum, and the recurrent flagellum, which is whiplash lies in a groove on the hypotheca called a sulcus (Figure B). They are important members of marine, freshwater, and brackish water environments. They also are main taxa that occur as zooxanthellae, photosynthetic symbionts in many animals, particularly the corals for which they provide food and the ability to sequester calcium carbonate (Figure C). Symbiosis in some taxa has led to parasitism. For example, Syndinium is parasitic within marine microcrustaceans (Figure J) whose cells it invades. Then, the feeding cell enlarges and ungdergoes mitosis without cytokinesis to form a plasmodium. Finally, gymnodinoid cells, which may be infective, emerge from the lysed host cell.

Some dinoflagellates are important as toxin producers and are principle contributors to paralytic shellfish poisoning (PSP), a condition that can occur when filter-feeding bivalves concentrate toxic algae, usually contributors to red tides, and sequester their poisons. Ptychodiscus (=Karenia) brevis is the organism responsible for red tides off the coast of Florida by the production of saxitoxin, a powerful neurotoxin that is second in its lethality only to botulism toxin (Figure B). Other red tide species occur along most coasts.

Many dinoflagellates are armored and produce a theca (also called an amphiesma) that is made of overlapping cellulosic plates (Figures D-F). Prorocentrum has reduced the theca to two major plates (Figure G). Some of the dinoflagellates are predaceous and feed on algae (Figure H) and other organisms. Pfiesteria is an organism that recently was discovered and has an elaborate lifecycle. It can produce neurotoxins and powerful tissue-dissolving enzymes that enable a population of these cells to kill and consume large fish like striped bass. Stylodinium (Figure H) and its relatives live as amoeboid cells that feed on filamentous algae after which they form a distinctive structure from which small gymnodinoid cells emerge.

Noctiluca (Figure I) is a large bioluminescent species that feeds on smaller protists in the marine plankton (I). Its cell is large, vacuolated, and it has a single feeding tentacle. When disturbed at night, Noctiluca, which literally means "night light" produces a soft green light when disturbed at night. I have witnessed concentrations of them in the Atlantic and Gulf of Mexico such that the sea and beach glowed an eerie green. Other more typical dinoflagellates like Pyrodinium, also are bioluminescent. They occur in great concentrations in mangrove lagoons in places like Puerto Rico where they play an important role in ecotourism on the island. Many dinoflagellates exhibit bioluminescence such that an older name of the phylum was Pyrrhophyta, the fire plants.

Most dinoflagellate species have a characteristic nucleus called a dinokaryon that has bottlebrush, condensed chromosomes and no histones. The seemingly primitive nature of the chromosomes and nucleus made them appear to be among the most primitive of the eukaryotes. However, molecular and ultrastructural work confirm that the dinokaryon is a derived character.

*A. An SEM micrograph of Gymnodinium. Note the ribbon-flagellum in the cingulum.*	B. An SEM micrograph of Karenia, the causative agent of red tide around Florida. Note the cells show the dorsal and ventral sides of the cells to illustrate the ribbon-like flagellum in the cingulum and a recurrent whiplash flagellum.	C. Zooxanthellae from the tissue of a coelenterate.	*D. A light micrograph of Ceratium, a large armored plankter of marine and freshwater environments.*
*E. An SEM micrograph of a Peridinium* zygote. Note the armored plates with intercalary bands between them.**	*F. An SEM micrograph of Dinophysis, a distinctive armored taxon with an apical cinculum and winged extensions of its hypothecal plates.*	*G. An SEM micrograph of Prorocentrum, which has two major plates and the flagellar insertions are at the apex (to the left of this cell).*	*H. SEM micrographs of Stylodinium* feeding on a green algal filament.**
*I. Noctiluca, a large vacuolated cell that has a feeding tentacle (see it emerge from the cell at right center) is a common member of the marine plankton and is bioluminescent.*	*J. Parasitic Syndinium* cells taken from an infected copepod.**	*K. Oxyrrhis, a motile cell that resembles Syndinium* motile cells but lacks a semblance of a cingulum.**	*L. Perkensus, a parasite of bivalve mollusks that seems to bridge the dinoflagellates and apicomplexans.*
Images taken from: A&E: The Systematic Biology Biodiversity Collection. B&I: http://www.marcobueno.net/arquivos_estudo/arquivo_estudo.asp?txtIDArquivo=343 C: http://www.coral.noaa.gov/themes/zooxlit.html D: http://www.bio.mtu.edu/the_wall/phycodisc/DINOPHYTA/gfx/CERATIUM.jpg		F: http://www.biol.tsukuba.ac.jp/~inouye/ino/d/Dinophysis1.GIF G: http://www.utas.edu.au/docs/plant_science/Aquatic/pplay/pplaysem03.jpg H: From a collection of photographs given to me by Lois Pfiester. J: http://www.vims.edu/~jeff/dinos.htm K&L: http://microscope.mbl.edu/scripts/

The dinoflagellates have been classified as algae, protists, and protozoa during the past 30 years [Taylor (1987; 1990), Lee (1980), Loeblich (1976), Dodge (1973), Sze (1986), Margulis and Schwartz (1988 and 1998), and Sleigh et al. (1984)] and usually divided the them into two groups. The taxonomy of Bold and Wynne (1985) was more complex with 4 classes, including the enigmatic Ebriids and a separate class for the prorocentrids. A newer taxonomic scheme by Taylor (1990) had only a single class with much more splitting among orders (up to 17). Traditionally, protozoological manuals such as Lee et al. (1985), Kudo (1966) and Grell (1973) lumped the dinoflagellates with all other flagellated unicells (and often with the amoeboid taxa)!

The dinoflagellates appeared to be unrelated to the other chlorophyll c-containing organisms (Dodge, 1989). Differences in nuclear chromosome structure led Dodge (1973) to suggest that the dinoflagellates occupied their own kingdom. However, Taylor (1976) suggested a connection between the dinoflagellates and ciliates, an association which was supported by the 5S rRNA sequence analyses of Hori and Osawa (1987, cited in Dodge 1989). More recent evidence (Gajadhar et al. 1991; Cavalier-Smith 1993; Patterson 1999; Taylor 1999; and Baldauf 2003) supported the association of the dinoflagellates, the Apicomplexata, and the Ciliata in a larger taxonomic entity called the Alveolata.

The following system has 4 classes with 11 orders. It was taken from Dodge and Lee (2000), a modification of Fensome et al. (1993). Unfortunately, even Dodge and Lee (2000), though quite recent, was based primarily on morphology and life history with little or no molecular confirmation. For example, Saunders et al. (1997) suggested that Noctiluca was a sister to the other dinoflagellates and some taxa, like Gymnodinium, were decidedly polyphyletic based on SSU rDNA. Saldarriaga et al. (2003) through the use of multiple protein phylogenies, show that Oxyrrhis [and Perkinsus] are sisters to the rest of the dinoflagellates (see Figures K and L, respectively). Thus, the following is presented as a provisional system only.

SYSTEMATIC BIOLOGY					THE ALVEOLATAE
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PHYLUM DINOFLAGELLATA