CERCOZOAE

Granuloreticulosa (GRAN-u-lo-re-tik-u-LO-sa) is formed from two Latin roots that mean little grain (granulum); and net-like (reticulum). The reference is to organisms that have grain-like tests from which an anastomosing web of pseudopodia emerges.

The Granuloreticulosa or Foraminifera (window bearers, and informally called forams) generally are members of the marine plankton and benthos where they can be very abundant and diverse. They capture their food by filtering the surrounding water with a reticulate, anastomosing pseudopodial web. Although Gromia and Micrometes (Figures A and B, respectively) are testate filopodial amoebae, they are not recognized as members of this phylum by Lee et al. (2000), while Allogromia (Figure C) is so recognized. Most of the remaining groups of forams make an internal test of calcium carbonate that may or may not be perforated by patterns of holes (the name "foraminifera" means "window-bearer"; Figures D-I). Often, the tests are quite complex with multiple chambers that increase in size and somewhat reminiscent of a Nautilus shell. They have a decided and complex alternation of generation and dimorphic nuclei like the ciliates.

Consider the life history of a complex foram like Metarotaliella. The gamont (1 in the attached life history) is haploid and associates with one or more other gamonts. They hold themselves in place by secreting a copulation jelly and then the gamonts undergo multiple mitoses with cytokineses to form many gametes. Compatible mating types fuse to form zygotes. The diploid cells begin to undergo mitosis without cytokinesis forming multinucleate cells. After they reach 4 nuclei, one enlarges and becomes polyploid to become the somatic nucleus (analogous to the macronucleus of a ciliate). As the cell enlarges, more calcareous chambers are added until finally the somatic cells undergo meiosis and the somatic nucleus aborts and is reabsorbed. The resulting 12 haploid nuclei accrete cytoplasm and become 1-chambered gamonts that begin to enlarge until copulation is triggered. Only through this complex alternation of generation can they increase numbers of cells. Many taxa (like Figures A-C) have only single chambers.

This type of cell and life history seems to have been quite successful. They appeared in the fossil record during the Cambrian and persisted to the present. However, their numbers and diversity allow forams to be among the most useful index fossils for marine strata. For that reason also they are among the most useful index fossils to use in oil exploration.

Nummulites is a very large (up to 6 cm in diameter) foram from the early Tertiary (Eocene). It looked like Figure E, and its name in Latin means little coin. They were so abundant in the shallow seas that covered part of Egypt, that their accumulated tests were major components of the thick beds of limestone from which the outer sheathing stones of the great pyramids were made.

Xenophylophorids are huge amoeboid cells that likely are benthic forams that have barium sulfate crystals in their spongy tests (Figure J). Some can be as large as 24 cm across (but very thin). There is little unanimity on their relationships, and the xenophyloporids may have to move to another kingdom.

A. Gromia, an atestate filopodial cell.

B. Micrometes has a simple organic test that has a single chamber.

C. Allogromia has a proteinaceous test with a single chamber.

D. Textularia has a test made of two off-set series of chambers that are partly mineralized and covered with sand grains.

E. Spirillina makes a planospiral test of calcite.

F. Miliola produces a test with a tight coil whose chambers are not separated by walls.

G. Laegena has a test of a single chamber made of optically-radiate calcite crystals. There is a single opening to the test.

H. Rotaliella has a multi-chambered perforate test wall with internal canal system.

I. Globigerina makes a wall of hyaline calcite with many regularly-arranged perforations. This genus is found in almost all latitudes from the tropics to the subpolar seas.

J. Cerelpemma, a xenophyophorid produces a lumpy irregular test that is sponge-like in its form. From 4-6km deep in the Pacific Ocean.

Images taken from:
A: http://protist.i.hosei.ac.jp/PDB/Images/Sarcodina/Gromia/sp_3.html
B: http://microscope.mbl.edu/baypaul/microscope/images/t_imgAZ/micrometes30_dhw.jpg
C: http://www.unige.ch/sciences/biologie/biani/msg/people/Fabien/Gromia2.htm
D: http://coastal.er.usgs.gov/biscayne-forams/gallery.html

E: http://www.ucmp.berkeley.edu/people/klf/KLF_files/Spirillina-cf.-vivipara.gif
F: http://microscope.mbl.edu/scripts/microscope.php?func=browseAlpha&letter=M&taxa=Miliola
G: http://www.ucmp.berkeley.edu/people/klf/Current_Projects.htm
H: http://www.ifremer.fr/crema/PGSauriau/foraminifera/taxonomy/rotaliina/Rotaliella.html
I: http://www.ucmp.berkeley.edu/people/klf/MicroGalleryLarge_files/Globigerina.jpg
J: Gooday and Tendal (2000)

As it is defined here, the taxonomy of the Granuloreticulosa is a modification of Lee (1990) and of Margulis and Schwartz (1988 and 1998) in which it is designated Pr-17 and PR-4, respectively. Kudo (1966), Grell (1976), Cushman (1980), Bovee (1985b), Bock et al. (1985) and Sleigh et al. (1984) lump the forams together with the amoebae, the slime molds and the actinopods. Forams are clearly different from the other "amoeboid" groups. The reticulopods produced by the forams are neither pseudopods nor actinopods (Margulis and Schwartz 1988 and 1998). Patterson (1989) suggests a connection with the chrysophyte complex based on the flagella produced by their motile cells (a view that he later -1999- repented of). Patterson (1999) gives the web-branching pseudopodial system as a possible synapomorphy for the group. The Xylophylophorids have been taxonomic nomads for a long time, but from the time of their discovery they have been referred to as benthic forams (Tendal 1972; Patterson 1999). Thus, I have kept the xenophyophorids together with the forams, but in their own class despite the misgivings of Lee et al. (2000).

Longet et al. (2003), Archibald et al. (2003), Archibald and Keeling (2004), and Nikolaev et al. (2004) show clear relationships between the foraminifera and taxa that are in the emerging supergroup called Cercozoa (or Rhizaria after Cavalier-Smith 2002). Baldauf (2003) and Keeling (2004) produced a synthesis of molecular and structural analyses that suggested the eukaryotes occupy eight (or five) major clades. Because of the diversity of form, complexity of life history and the occurrence of dimorphic nuclei, all of which argue for raising the Granureticulosa to phylum-level rank, I present the following system.

SYSTEMATIC BIOLOGY					THE CERCOZOAE
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PHYLUM GRANULORETICULOSA