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Monosiga (mon-owe-sigh-ga), a choanoflagellate (collar flagellate), here many cells have colonised a small piece of detritus. Each globular cell has a conical collar around the single apical flagellum. Phase contrast.

Portrait of Monosiga, a choanoflagellate without a visible lorica. A collar of pseudopodia which trap food particles surrounds a central flagellum. The particles are transported to the base of the collar where they are ingested. This is an unusually large specimen. The cell body is usually about 5 microns in length. The nucleus, food vacuoles and contractile vacuole are well seen here. This species is stalked while others are not, the cell body attaching directly to the substrate. From a freshwater pond near Boise, Idaho. Phase contrast.

Monosiga ovata Kent, 1880. The ovoid cell is approximately 4 microns long or 15 microns when measured from the tip of the flagellum to the distal end of the stalk. At the anterior end of the cell a ring of 20-25 tentacles, almost equal in length, forms a collar which encircles the single flagellum. The latter projects beyond the tentacles and terminates in a conspicuous hair point. The cell body and the base of the tentacles are closely invested by a delicate membranous sheath and this tapers posteriorly to form the stalk or peduncle which attaches the cell to the substratum. The apparent looseness of the sheath in shadowcast whole mounts is probably caused by the shrinkage of the protoplast during drying. Transverse sections of the cell in the region of the tentacles and cell body show that the sheath fits closely although it is ridged at intervals. That part forming the stalk sometimes has a fibrillar appearance but it is not clear whether this is a partial disintegration caused by drying or a genuine arrangement for attaching the cell to the substratum. In section the sheath is seen to be composed of two regularly spaced layers, the surfaces of which are covered with a fine fibrillar deposit possibly of mucilage.

Monosiga brevicollis Ruinen, 1938. The shape of the cells is variable. The resting cells are 4-6 microns long, more or less spherical. When swimming, the posterior end is sharpened, the shape becomes more ovoid and the collar is spread out. The collar is 0.5 cell length, the flagellum about 4.5. cell length. The cytoplasm is fine-grained to hyaline and contains strongly refractile grains. A vacuole lies in the posterior part of the cell.

PRESS RELEASE  Can you hear me now? Primitive microbe bests human in complexity of cell communication genes July 08, 2008 LA JOLLA, CA   When it comes to cellular communication networks, a primitive singlecelled microbe that answers to the name of Monosiga brevicollis has a leg up on animals composed of billions of cells. It commands a signaling network more elaborate and diverse than found in any multicellular organism higher up on the evolutionary tree, researchers at the Salk Institute for Biological Studies have discovered. Their study, published during the week of July 7-11 in the online edition of the Proceedings of the National Academy of Science, unearthed the remarkable count of 128 tyrosine kinase genes, 38 more than found in humans. These kinases transmit essential signals for cell growth, stasis, and death. Though their activity is tightly regulated in normal cells, out-of-control kinases are a major cause of cancer. Many successful cancer drugs – such as Gleevec, which is used for the treatment of leukemia, – specifically target wayward tyrosine kinases. This treasure trove of diverse and novel tyrosine kinases took the lead author of the study, Gerard Manning, who heads the Razavi-Newman Center for Bioinformatics, by surprise since it was long thought that tyrosine kinases are restricted to multicellular animals where they handle communication between cells. Manning says that they were absolutely stunned,based on past work, we had expected maybe a handful of these kinases but instead discovered that this primitive organism has a record number of them. Two other essential parts of the tyrosine kinase network – PTP and SH2 genes – are also more numerous than in any other genome, showing that it is the whole network that is elaborated here.   The 100 trillion cells in our bodies require elaborate communication systems to coordinating their activities. Tyrosine kinases, extremely well-studied enzymes that act as receivers for external cues such as a growth signals and relay their message within cells by attaching tiny phosphate groups to proteins, are a vital part or this communication system.  At first glance, Monosiga brevicollis, which belongs to the group of choanoflagellates – microscopic, aquatic organisms that occupy the grey area between fungal and animal kingdoms – has little in common with multicellular animals that need to co-ordinate the activities of billions of cells. But its distinctive architecture – a collar of tentacle surrounding a whip-like tail known as flagellum – has the same basic structure as collar cells that aggregate to form sponges, which are considered the most primitive multicellular organisms or metazoans. Because of their key evolutionary position, M. brevicollis was selected as a representative choanoflagellate for whole genome sequencing. Choanoflagellates are like the first cousins of animals and their genome allows us a glimpse into the evolutionary origin of animals - says Manning. The Monosiga kinases are more divergent than anything previously seen in animals, which may help scientists understand the fundamentals of how all tyrosine kinase signaling works. Despite their extreme diversity, Monosiga kinases time and again arrive at the same solution to a problem, as do animal kinases, but using a distinct method for instance to create a sensor structure that emerges from the cell, or to target a kinase to a specific part of the cell. Manning says that this convergent evolution suggests that there are only a limited number of ways build a functional network from these components. With all this new information, one obvious question remains unanswered: what is a singlecelled organism doing with all this communications gear? Manning says: - We do not have a clue!, but this discovery is the first step in finding out.  For more information  Researchers who also contributed to the work include Yufeng Zhai, Ph.D. from the Salk Institute, Susan L. Young, Ph.D., in the Center for Integrative Genomics at the University of California, Berkeley and W. Todd Miller, Ph. D. in the Department of Physiology and Biophysics at Stony Brook University, Stony Brook.

Monosiga marina marina Paasche, 1961. We have not been able to obtain a description of this variety available at this time.

Monosiga marina minima Paasche, 1961. Cell body fusiform, length 4-8 microns, width about 2 microns Collar distally constricted, 2 microns long and equally wide. Typically without basal prolongation or stalk.

Proterospongia (pro-terr-ow-sponge-ee-a) a collar flagellate (choanoflagellate), normally regarded as forming flat colonised, but in culture the capacity to form colonies can be lost, to leave cells indistinguishable from the solitary Monosiga. With apical flagellum and a collar, only the edge of which is seen as a dark line on either side of the flagellum. Phase contrast.

Detail of Sphaeroeca volvox showing individual cells with a single anterior emergent flagellum with surrounding collar of microvilli. Posteriorly the cells are drawn out into a long thread-like process, which may adhere to those of other cells in the center of the spherical colony. From temporary rainwater pool near Boise, Idaho. Brightfield illumination.

Portrait of colorless, motile, colonial choanoflagellate, Sphaeroeca volvox. Individual cells have no visible periplast by light microscopy. Cell shape is approximately pyriform. There is one anterior emergent flagellum with a short circumferential collar of microvilli. The posterior end of the cell is drawn out into a long thread, which may join with those of other cells. Spherical colonies are composed of large numbers of cells. From temporary rainwater pool near Boise, Idaho. DIC.

Sphaeroeca are colonial choanoflagellates, with a pyriform or ovoid cell bearing one long flagellum arising from a collar and a pointed posterior end. Cells are arranged on surface of a sphere with flagella directed outwards. Sphaeroeca volvox Lauterborn forms spherical colonies 250-500 microns diameter, individual cells 5-6 microns long and flagellum 36-40 microns long, contractile vacuoles at the posterior end. Planktonic in freshwater habitats.

Sphaeroeca are colonial choanoflagellates, with a pyriform or ovoid cell bearing one long flagellum arising from a collar and a pointed posterior end. Cells are arranged on surface of a sphere with flagella directed outwards. Sphaeroeca volvox Lauterborn forms spherical colonies 250-500 microns diameter, individual cells 5-6 microns long and flagellum 36-40 microns long, contractile vacuoles at the posterior end. Planktonic in freshwater habitats.

Sphaeroeca are colonial choanoflagellates, with a pyriform or ovoid cell bearing one long flagellum arising from a collar and a pointed posterior end. Cells are arranged on surface of a sphere with flagella directed outwards. Sphaeroeca volvox Lauterborn forms spherical colonies 250-500 microns diameter, individual cells 5-6 microns long and flagellum 36-40 microns long, contractile vacuoles at the posterior end. Planktonic in freshwater habitats.

Kentrosiga echina Tong, 1997. Cells are solitary or in linear colonies of 2 -5 individuals. Cells 2.5-7.5 x 4.5-9.5 microns, flagellum 24-32 microns, surrounded by a short collar of tentacles (~7 microns). About 6-10 bristles (rather rigid cytoplasmic extentions) project from the cell surface. The protoplast is enclosed within a fine, flask-shaped investment which extends a short way above the cell.

Choanoeca (ko-an-o-eek-a), an unusual loricate collar flagellate (choanoflagellate) in that the usual form is without a flagellum. Flagellated motile stage is occasionally produced. Widely dispersed pseudopodial elements of the collar are evident in this image. Phase contrast.

Choanoeca (ko-an-o-eek-a), an unusual loricate collar flagellate (choanoflagellate) in that the usual form is without a flagellum. Flagellated motile stage is occasionally produced. Widely dispersed pseudopodial elements of the collar are evident in this image. Differential interference contrast.

Choanoeca perplexa Ellis, 1930. Choanoflagellate cell, solitary, piriform, neck considerably elongated, length of cell (extended): 4.5 to 7 microns Lorica vasiform, more or less closely investing cell, sessile or with short peduncle. Diameter of collar at mouth: 12-18 microns at the normal angle of expanse, about 75degrees, the extreme angles of expanse are 10 degrees and 90 degrees - that is, at right angles with major axis of the cell. Flagellum entirely absent in normal adult cell, but temporarily produced, just before cell-fission, for locomotion. Nucleus normal. One contractile vacuole, basal. The collar can rapidly transform from maximum to minimum expanse, the act strongly resembling the sudden closing of an umbrella. The shape of the lorica is that of a short-necked vase with a slightly everted lip and globular body tapering, more or less abruptly, to a point. The peduncle is obviously an extension, 2-6 microns long of the lorica.

Diploeca hemisphaerica Norris, 1965. Cell ovate to hemispherical, enclosed within a hemispherically-shaped lorica. Lorica wall of two parts, an outer, yellowish, thick wall enclosing a thin, colorless wall that protrudes a short distance beyond opening of thick wall. Outer wall expanded anteriorly. Lorica 5-6.5 microns wide, 4.5-4.8 microns long, pore of outer lorica 1.8 microns dia., inner wall flared to 3.2 microns

Diploeca neustophila Norris, 1965. Cells obovoid, narrower end with colar and flagellum. Cell within a lorica composed of two similar walls, both walls expanded, inner wall extending beyond rim of outer wall. Collar very long and usually extending far beyond lorica. Cell 6 microns long, 3 microns wide, lorica 4.5-5 microns wide, 7-9 microns long. Inner wall extending approximately 2 microns beyond rim of outer wall. Collar up to 8 microns long. Opening of lorica approximately 7 microns diameter.

Diploeca placita Ellis, 1930. Cell, oval, with long neck extending well above the lorica mouth, partly or wholly filling lorica. Lorica proper is elongate ovate, brown in colour, and attached. Nucleus normal. One contractile vacuole. The length of thickened (double) lorica is 8 microns The length of neck of lorica, 2 microns, greatest width of lorica, 4 microns, cell extended, 8-9 microns, cell width, 3 microns

Pachysoeca (pack-ee-sew-eek-a) a choanoflagellate which lives in a thick walled organic lorica,. The body gives rise to a long narrow neck which itself produces a collar around the base of the single flagellum. The lorica has broken on the left side. Phase contrast.