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PHYLUM CHRYSOPHYTA

INTRODUCTION TO THE CHRYSOPHYTA

Chrysophyta (kri-SO-fa-ta) is derived from two Greek roots meaning golden (chryso - χρυσό); and plant (phyto -φυτό).  The reference is to the golden cast to many taxa of the phylum.  The color comes from a dominance of golden-colored secondary pigments.

The chrysophytes are, as the name implies, the "golden" algae.  The golden color of the chrysophyte chloroplast (chromoplast) is a consequence of the dominance of secondary pigments, particularly β-carotene, fucoxanthin and other xanthophylls.  The primary photosynthetic pigments are chlorophylls a and c₁ as well as c₂.  The cells of chrysophytes are naked or covered with silicaceous scales.  

The chrysophytes are divided into two major groups: the chrysomonads and the silicomonads.  Chrysomonads range in form from motile unicells to loose palmelloid aggregates to filaments (Figures A-D).  They are united by the formation of particular types of motile cells, which resemble Ochromonas (Figure A) in that the heterodynamic flagella are inserted nearly apically with a light sensitive swelling at the base of the recurrent whiplash flagellum.  An eyespot that is part of one of the chloroplasts is associated with the flagellar swelling.  Though a sexual life history is unknown in Ochromonas, other taxa do exhibit sexual fusion and the formation of a resting cyst, the statocyst.  Dinobryon, for example, is isogamous and individual vegetative cells seem to function as facultative gametes.  At the onset of sexual reproduction, vegetative cells leave their loricas and begin to fuse.  Then, a silicaceous urn-like cyst begins to form within the cell, and the cell (It does not seem to be a zygote at this point, that is, nuclear fusion has not yet occurred.) "pours itself into the statospore urn.  After that, it corks the bottle with an organic material.  During the cyst stage, fusion and meiosis must occur because four motile vegetative cells emerge from the statospore when it germinates.   

Unlike the chrysomonads, which are almost exclusively freshwater, the silicomonads are marine.  Their cells have a single, anteriorly-directed tinsel flagellum and a very small whiplash flagellum.  Dictyocha (Figure E) forms a delicate silicaceous basket around which the frothy cytoplasm of the vegetative cell enwraps itself.  They do form rounded motile swarmer cells (gametes?), but further details of a sexual life history are unknown.  They can form blooms in the ocean plankton.  Their star-like external skeletons preserve well so that they do have a fossil history.

SYNOPTIC DESCRIPTION OF THE CHRYSOPHYTA

SYSTEMATICS OF THE CHRYSOPHYTA

Traditionally, phycologists like Sze (1986) and Bold and Wynne (1985) use the term "chrysophytes" to lump together taxa like the haptophytes, xanthophytes, chrysophytes, diatoms and phaeophytes.  Protozoologists like Kudo (1966), Grell (1976), and Lee et al. (1985) consider the chrysophytes to be a subgroup of the phytomastigophora (pigmented flagellated unicells).

I follow the taxonomic systems of Margulis and Schwartz (1988) and Sleigh et al. (1984) in which the chrysophytes are recognized as a distinct, natural group. The taxonomy of this phylum is a modification of Margulis and Schwartz (1988 and 1998) in which it is designated Pr-4 and Pr-13, respectively. I have adopted the system proposed by Kristiansen (1982, cited in Bold and Wynne 1985) and Kristiansen (1990) in which the orders are based on the vegetative forms rather than the artificial system used by Lee (1980) in which the orders are defined by the number of flagella, a trait which has proven to be variable in this group. Although Patterson (1989) casts doubt on the association of Pedinellines with the other chrysophytes, I have retained it as an order.

Taylor (1976) suggests that the chrysophytes form the stem from which the haptophytes, diatoms, the phaeophytes and choanoflagellates evolved. This "chrysophyte complex" is called the Chromophytes, and Cavalier-Smith (1989) indicates that they should be considered as a new kingdom called the Chromista.  Indeed, Patterson (1999) summarizes work that suggests the chrysophytes (as I consider them here) are paraphyletic within the heterokont tree.  The tree of Sogin and Patterson (Tree of Life Project) further supports this view.  Clearly, the chrysophytes require more work, and I retain them as a provisional phylum.

HIERARCHICAL CLASSIFICATION OF THE CHRYSOPHYTA

This page is maintained by Jack R. Holt. Last revised: 03/17/2008.