SYSTEMATIC BIOLOGY					THE CERCOZOAE
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PHYLUM CERCOMONADA

INTRODUCTION TO THE CERCOMONADA

Cercomonada (sur-ko-mo-NA-da) is derived from two Greek roots that mean tail (kerkos -κέρκος); and unit (monada -μονάδα).  The phylum is named for a common genus, Cercomonas, which is a motile cell with heterodynamic flagella.  The trailing flagellum looks like a tail.

The cercomonads include a diverse collection of unicells that are testate, motile, radiolarian, and heliozoid (Figures A-E).  The group is defined strictly by molecular ssu-rRNA and actin molecular phylogeny (mainly Nikolaev et al. 2004).  Thus, there are no clear synapomorphies to define them.  All can produce filopodia, but this is a synapomorphy of the Cercozoae, in general.  By and large, groups of the cercomonads were orphan taxa, unaffiliated with other groups and defined as sisterless groups by Patterson (1999).  Members of the cercomonads resemble carpediemonads and other excavates, testate amoebae, and heliozoans. 

The phaeodarians, a group of organisms once considered sarcodines (amoeboid animals) and affiliated with the radiolaria (a group of biomineralized heliozoan-like cells: polycyctines and acantharians), have a cytoskeleton that is mineralized with amorphous silica.  They are rare members of the marine plankton and discovered only near the end of the 19th century during the voyages of discovery on the open ocean.  The expedition of the HMS Challenger (1872-1876) was one such voyage, which was charged with studying the oceans of the world.   To that end, it carried biologists, chemists, physicists, geologists, and archaeologists.  During the four years of discovery, the ship circumnavigated the globe, took many soundings, temperature profiles, and bottom dredges.  In the process, the expedition catalogued 4717 new species, many of them from the plankton.  In fact, the unexpected diversity of the plankton in the ocean was one of the greatest discoveries made by the Challenger and her crew.  Challengeron (see Figure F) was one of the phaeodarians discovered by and named after the expedition.  It was bilaterally-symmetrical, and, like other phaeodarians, had an internal capsule that surrounded the nucleus and a bilaterally-symmetrical outer capsule.  The feeding axopods originated at one end of the internal capsule and emerged from the outer capsule at the bottom of the illustration in Figure F.  Ernst Haekel, was a prolific writer, researcher, and artist, who popularized many of the organisms collected by the Challenger and other expeditions of the late 19th and early 20th centuries.  Figure F is his illustration of an organism that he described and named.

A. An SEM micrograph of the scaly test of Euglypha from the bottom of a soft water pond in central PA.	B. A DIC micrograph of Cercomonas, a motile cell with heterodynamic flagella.  The recurrent flagellum lies in a ventral groove.	C. An illustration of Aulocantha.  This taxon has both tangential needles and denticulate radial spines.
D. An illustration of the mineralized cytoskeleton of Aulosphaera in the the peripheral network is joined in a triangular pattern.  The radial spines emerge from the joints of the network.	E. An illustration of Clathurlina showing the stalked heliozoan structure with the filopodia emerging from openings in the organic capsule surrounding the cell.	F. Challengeron, an illustration by Ernst Haekel (from his Kunstformen der Natur (Artforms in Nature).  Haekel also described this particular species, C. wyvillei.
Images taken from: A: The Systematic Biology Biodiversity Collection B: http://microscope.mbl.edu/baypaul/microscope/images/t_imgAZ/cercomonas2_lpw.jpg C: http://microscope.mbl.edu/scripts/microscope.php?func=browseAlpha&letter=A&taxa=Aulacantha D: http://microscope.mbl.edu/baypaul/microscope/images/t_imgAZ/aulosphaeratrigonopar10_ehw.jpg E-F: Grell (1973)

SYNOPTIC DESCRIPTION OF THE CERCOMONADA

SYSTEMATICS OF THE CERCOMONADA

The "core cercozoa" has emerged as a coalescence of sisterless taxa from the last years of the 1990s to 2005 (Patterson 1999, Kuhn et al. 2000; Wylezich et al. 2002; Archibald et al. 2003; Longet et al. 2003, Nikolaev et al. 2003; Cavalier-Smith and Chao 2003; Archibald and Keeling 2004; Nikolaev et al. 2004).  The earliest work (e.g. Kuhn 2000) focused on the cercomonads, a group of amoeboflagellate taxa.  The curious results of the initial work confirmed a relationship between the cercozoans and the foraminifera (Archibald and Keeling 2004; Archibald et al. 2003; and Longet et al. 2003).  

HIERARCHICAL CLASSIFICATION OF THE CERCOMONADA

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