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PHYLUM EUSTIGMATOPHYTA

INTRODUCTION TO THE EUSTIGMATOPHYTA

Eustigmatophyta (u-stig-ma-TA-fa-ta) is derived from three Greeks roots that mean true or good (eu - ευ); spot (stigma - στίγμα); and plant (phyto -φυτό).  The reference is to the eyespot (also called a stigma) in the zoospores.

The eustigs are few in number and make up a relatively new group of organisms.   One, Nannochloropsis, is a member of the marine picoplankton, but most tend to be coccoid algae in soil or freshwater (Figures A&B).  Hibberd and Leedale (1970) studied the ultrastructure of the zoospores of certain coccoid cells and found that they made a stigma or eyespot outside of the plastid but near a swelling at the base of the flagellum (Figure C).  This arrangement is similar to that of the euglenoids rather than the chrysophytes or xanthophytes, whose eyespots are contained within the membranes of one of the chloroplasts.  In fact, this character found in the zoospore served to separate the eustigs from the xanthophytes, with which they had once been classified.

A. Coccoid cells of Nannochloropsis, a tiny marine plankter.	B. Chlorobotrys (formerly known as Chlorococcum) is a common plankter in acid bogs and fens.  In greenhouses it is found growing on the outsides of clay pots.	C. A TEM micrograph of a eustig zoospore.  It shows the characteristic eustgma (an eyespot that is outside of the chloroplast, labeled E).  * = expanded region of the flagellum,  N = nucleus, M = mitochondrion; P = plastid.
Images taken from: A: http://microscope.mbl.edu/scripts/microscope.php?func=imgDetail&imageID=2613 B: http://www.glerl.noaa.gov/seagrant/GLWL/Algae/Chrysophyta/Cards/Chlorobotrys.html C: Graham and Wilcox (2000)

SYNOPTIC DESCRIPTION OF THE EUSTIGMATOPHYTA

SYSTEMATICS OF THE EUSTIGMATOPHYTA

Prior to the recognition by Hibberd and Leedale (1970) of the unique stucture of the eustig motile cell, members of the Eustigmatophyta were placed in the xanthophytes. Now many sources (e.g. Bold and Wynne 1985; Sze 1986; and Lee 1980 & 1989) consider the eustigs to be a class within the chrysophytes. Graham and Wilcox (2000) refer to the photosynthetic heterokonts as Ochrophytes and use Cavalier-Smith and Chao (1996) to support their association with the chrysophytes, raphidiophytes, and the synurophytes.  Margulis and Schwartz (1988, Pr-10), Sleigh et al. (1984), and Hibberd (1990) consider the differences between the eustigs, xanthophytes and chrysophytes sufficient to place them into separate phyla. The phylogeny of Taylor (1976) shows the eustigs emerging from a line near the chloromonads (now called raphidiophytes) and prior to the chrysophyte complex. The analysis of Dodge (1973) shows the eustigs occupying a link between the euglenoids and xanthophytes (or chrysophyte complex).  I follow the phylogeny of Sogin and Patterson (Tree of Life Project) in that they form a natural group and should be united with other heterokont phyla (although the particular relationships seem to be obscure).

HIERARCHICAL CLASSIFICATION OF THE EUSTIGMATOPHYTA

Revised: 03/17/2008