DESCRIPTION OF THE PHYLUM CHRYSOPHYTA (PASCHER 1914)

EUKARYA> CHROMALVEOLATA> HETEROKONTAE> 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.

INTRODUCTION TO THE CHRYSOPHYTA The chrysophytes are, as the name implies, the “golden” algae. The golden color of the chrysophyte chloroplast ( chromoplast (text with tooltip) Chromoplast is the general term for a photosynthetic organelle. Technically, a chloroplast is a particular chromoplast in which the dominant chlorophylls are A and B. ) is a consequence of the dominance of secondary pigments, particularly β-carotene, fucoxanthin (text with tooltip) Fucoxanthin is a carotenoid secondary photosynthetic pigment that occurs in many of the photosynthetic eukaryotes like the heterokonts and haptotists. and other xanthophylls. The primary photosynthetic pigments are chlorophylls a and c1 as well as c2 (text with tooltip) Chlorophyll C is a variant of Chlorophyll A. and a secondary photosynthetic pigment in the many of the photosynthetic heterokonts and dinoflagellates. . The cells of chrysophytes are naked, covered with cellulosic walls (Figure 1), loricas (Figure 2), or scales (text with tooltip) Protist scales are regular overlapping structures on the outside of the cell. They may be organic, silicaceous, or carbonaceous and may serve as an articulated cell wall. Scales may occur on the cells of a range of unrelated taxa. (organic or silicaceous). The chrysophytes are divided into two major groups: the chrysomonads and the synurids. Both groups superficially resemble each other in that they range from unicells to colonies and occur mainly in freshwater. Chrysomonads range in form from motile unicells to loose palmelloid (text with tooltip) Palmelloid (adj) describes a colonial form in which cells are dispersed in a mucilaginous matrix. aggregates to filaments. They are united by the formation of particular types of motile cells, which resemble Ochromonas (Figure 1) 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 spore, the statospore (text with tooltip) Statospores are resting spores (zygospores) produced by chrysophytes and xanthophytes. They are produced within the cell and have a plug of organic material in the chrysophytes. (Figure 5). Dinobryon, for example, is isogamous (text with tooltip) Isogamous (adj) describes sexual reproduction in which the gametes are structurally identical. and individual vegetative cells seem to function as facultative gametes. At the onset of sexual reproduction, vegetative cells leave their loricas (text with tooltip) A lorica is a covering that occurs outside of the cell membrane. It is secreted by the cell and usually is organic. Loricas do not completely enclose the cell. Periplasts, structures similar to loricas do enclose the cell. Lorica stands for armour. 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. Andersen (1987) showed that Synura and a set of related taxa were were different enough to be place in a different class, Synuraphyceae. Like the chrysomonads, taxa in this group can be unicells to colonies. They do make scales that are bilaterally symmetrical, they do not utilize chlorophyll c2 , they do not have eyespots or typical stramenopile chloroplasts. The most familiar taxa are Mallomonas (a heavily-scaled unicell) and Synura (a motile colony. 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). The taxonomic systems of Margulis and Schwartz (1988) and Sleigh et al. (1984) recognized the chrysophytes as a distinct group. The former taxonomy of this phylum was defined by Kristiansen (1982, cited in Bold and Wynne 1985) and Kristiansen (1990) in which the orders were based on vegetative forms rather than the “protozoan” system used by Lee (1980) in which the orders were defined by the number of flagella. 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 we consider them here) are paraphyletic within the heterokont tree. The tree of Sogin and Patterson (Tree of Life Project) further supports this view. The revision of Andersen (1987) was slow to be accepted by working phycologists; however, the sister relationship between the Chrysophyceae and Synuraphyceae has been recovered in most molecular phylogenetic analyses (e.g. Andersen 2004; Brown and Sorhannus 2010, and Yang et al. 2012; see Figure 6). This new view of the chrysophytes is much narrower than the taxonomic system of 20 years ago and former orders are separated in other chromophyte phyla.

FIGURE 1. Ochromonas is a common motile heterokont unicell. Image from http://silicasecchidisk.conncoll.edu/LucidKeys/Carolina_Key/html/Ochromonas_Main.html	FIGURE 2. Dinobryon is a motile colony of Ochromonas-like cells, each in a lorica, all of which hang together in a bush-like pattern. Image from http://www.ac-rennes.fr/pedagogie/svt/photo/microalg/dinobry.htm	FIGURE 3. Statospore of Dinobryon still attached to the colony. Image from the Systematics Biodiversity Image Archive	FIGURE 4. Motile cell of Mallomonas. The hairy appearance is due to long extensions of the scales that cover the cell. Image from Sea Grant NOAA	FIGURE 5. Motile colony of Synura. Image by Deuterostome, used according to CC License

FIGURE 6. A cladogram showing the relationship of the chrysophyte taxa (in shaded box) within the heterokonts (taxa in bold). Oc is the Ochrophyta clade, the photosynthetic taxa. The topology of this cladogram was informed by Andersen (2004), Brown and Sorhannus (2010), and Yang et al. (2012).

LITERATURE CITED Andersen, R. A. 2004a. Biology and systematics of heterokont and haptophyte algae. American Journal of Botany. 91(10): 1508-1508. Baldauf, S. L. 2003a. The deep roots of eukaryotes. Science. 300 (5626): 1701-1703. Bold, H. C. and M. J. Wynne. 1985. Introduction to the Algae. 2nd Edition. Prentice-Hall, Inc. Englewood Cliffs. NJ. Brown, J. W. and U. Sorhannus. 2010. A molecular genetic timescale for the diversification of autotrophic stramenopiles (Ochrophyta): substantive underestimation of putative fossil ages. PLoS ONE 5(9): e12759. doi:10.1371/journal.pone.0012759. Cavalier-Smith, T. 1989. The Kingdom Chromista. In: Green, J.C., B.S.C. Leadbeater, and W.L. Diver, eds. The Chromophyte Algae: Problems and Perspectives. Systematics Association Special Volume No. 38. Clarendon Press. Oxford. pp. 381-407. Grell, K. G. 1973. Protozoology. Springer-Verlag. New York. Kristiansen, J. 1990. Chrysophyta. In: Margulis, L., J.O. Corliss, M. Melkonian, and D.J. Chapman, eds. 1990. Handbook of the Protoctista; the structure, cultivation, habits and life histories of the eukaryotic microorganisms and their descendants exclusive of animals, plants and fungi. Jones and Bartlett Publishers. Boston. pp. 438-453. Kudo, R.R. 1966. Protozoology. 5th ed. Charles C. Thomas Publisher. Springfield. Lee, J. J., S. H. Hunter, and E. C. Bovee, eds. 1985. An Illustrated Guide to the Protozoa. Society of Protozoologists. Lawrence, Kansas. Lee, R. E. 1980. Phycology. Cambridge University Press. Cambridge. Margulis, L. and K. Schwartz. 1988. Five kingdoms, an illustrated guide to the phyla of life on earth. 2nd Edition. W.H. Freeman and Co. New York. Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York. Pascher A. 1914. Über Flagellaten und Algen. Berichte der Deutschen botanischen Gesellschaft. 32: 136-60. Patterson, D. J. 1989. Stramenopiles: chromophytes from a protistan perspective. In: Green, J. C., B. S. C. Leadbeater, and W. L. Diver, eds. The chromophyte algae, problems and perspectives. Systematics Association Special Volume No. 38. Clarendon Press. Oxford. pp. 357-379. Patterson, D. J. 1999. The diversity of eukaryotes. American Naturalist. 154 (Suppl.): S96–S124. Sleigh, M.A., J.D. Dodge and D.J. Patterson. 1984. Kingdom Protista. In: Barnes, R.K.S., ed. A Synoptic Classification of Living Organisms. Sinauer Associates, Inc. Sunderland, Mass. Sogin, M. L. and D. J. Patterson. 1995. Stramenopiles. Version 01 January 1995 (under construction). http://tolweb.org/Stramenopiles/2380/1995.01.01 In: The Tree of Life Web Project, http://tolweb.org/ Sze, P. 1986. A Biology of the Algae. Wm. C. Brown Publishers. Dubuque, Iowa. Taylor, F. J. R. 1976. Flagellate Phylogeny: A Study in Conflicts. J. Protozool. 23: 28-40. Yang, E. C., G. H. Boo, H. J. Kim, S. M. Cho, S. M. Boo, R. A. Andersen, and H. S. Yoon. 2012. Supermatrix data highlight the phylogenetic relationships of photosynthetic stramenopiles. Protist. 163: 217-231.

By Jack R. Holt. Last revised: 02/24/2015