''Gonium'' is a genus of colonial

algae Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from ...

, a member of the order

Chlamydomonadales Chlamydomonadales, also known as Volvocales, are an order of flagellated or pseudociliated green algae, specifically of the Chlorophyceae.See the NCBIbr>webpage on Chlamydomonadales Data extracted from the Chlamydomonadales can form planar or ...

. Typical colonies have 4 to 16 cells, all the same size, arranged in a flat plate, with no anterior-posterior differentiation. In a colony of 16 cells, four are in the center, and the other 12 are on the four sides, three each. A description by G.M. Smith (1920, p. 94):Smith, GM. Phytoplankton of Inland Lakes of Wisconsin, Part I, Wisconsin Geological and Natural History Survey, Madison, WI. (1920).

''Gonium'' Mueller 1773: Colonies of 4-8-16 cells arranged in a flat quadrangular plate and embedded in a common gelatinous matrix or connected by broad gelatinous strands. Cells ovoid to
pyriform Piriform, sometimes ''pyriform'', means pear-shaped (from Latin ''pirum'' "pear" and ''forma'' "shape"). It may also refer to: Going pear-shaped * Going wrong or going pear-shaped Anatomy * Piriform aperture, more commonly known as anterior ...
, with a single cup-shaped
chloroplast A chloroplast () is a type of membrane-bound organelle known as a plastid that conducts photosynthesis mostly in plant and algal cells. The photosynthetic pigment chlorophyll captures the energy from sunlight, converts it, and stores it ...
containing one
pyrenoid Pyrenoids are sub-cellular micro-compartments found in chloroplasts of many algae,Giordano, M., Beardall, J., & Raven, J. A. (2005). CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. Annu. Rev. Plant Bio ...
. Each cell with two
cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...
of equal length, contractile
vacuole A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic ...
s at the base of the cilia, and an eyespot. Four- and eight-celled colonies with the cilia on the same side ; sixteen-celled colonies with the four central cells having their cilia on the same side and the twelve marginal cells with radially arranged cilia. Asexual reproduction by simultaneous division of all cells in the colony to form autocolonies, or by a formation of 2-4
zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or m ...
s in each cell. Sexual reproduction
isogamous Isogamy is a form of sexual reproduction that involves gametes of the same morphology (indistinguishable in shape and size), found in most unicellular eukaryotes. Because both gametes look alike, they generally cannot be classified as male or f ...
, by a fusion of biciliate zoogametes.

Evolution

The genus ''Gonium'' represents species closely related to single celled ''

Chlamydomonas ''Chlamydomonas'' is a genus of green algae consisting of about 150 speciesSmith, G.M. 1955 ''Cryptogamic Botany Volume 1. Algae and Fungi'' McGraw-Hill Book Company Inc of unicellular flagellates, found in stagnant water and on damp soil, ...

'' and multicellular differentiated ''

Volvox ''Volvox'' is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. It forms spherical colonies of up to 50,000 cells. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 170 ...

''. The order

Volvocales Chlamydomonadales, also known as Volvocales, are an order of flagellated or pseudociliated green algae, specifically of the Chlorophyceae.See the NCBIbr>webpage on Chlamydomonadales Data extracted from the Chlamydomonadales can form planar or ...

has long been a well recognized model system for the study of multicellular evolution. ''Gonium'' and the family Tetrabaenaceae contain species representative of colony formation among unicells. ''Goniums morphology of colonies of alike cells suggest it is more genetically similar to ''

'' than ''

'', a fact confirmed by phylogenetic analysis. The

have been hypothesized to have evolved in twelve discrete steps. Gonium represents the first six evolutionary steps of multicellularity; (1) incomplete cytokinesis, (2) partial inversion, (3) rotation of the basal bodies, (4) organismal polarity, (5) transformation of the cell wall into extra-cellular matrix (ECM), (6) genetic control of cell number. Although the exact order and progression through David Kirk's twelve steps of multicellular evolution are probably not necessarily linear and each occurs more dynamically than originally thought.

Life cycle

''Gonium'' being evolutionarily related to ''

'' has a life cycle that is derivative of that of ''Chlamydomonas''. ''Gonium'' cells grow asexually as colonies of either 4, 8 or 16 colonial cells. Cell and colony growth of ''Gonium'' is uncoupled from cell division just like ''Chlamydomonas'' and each cell within the colony divides by multiple-fission. Thus, each cell within the colony will divide 2, 3 or 4 times, thus producing 2^"n" daughter cells, or 4, 8 or 16 cells within the colony. Unlike ''Chlamydomonas'' where each of the daughter cells separate from each other, ''Gonium'' daughter cells remain attached to each other in their ECM. The sexual cycle of ''Gonium'' is also very similar to that of ''Chlamydomonas''. The sexual program of ''Gonium'' is induced by nitrogen deprivation where each vegetative cell within the colony differentiates in gametes. ''Gonium'' gametes are isogomous, or equal-sized, and unicellular. Thus unicellular ''Gonium'' gametes break apart from the multicellular colonies when the sexual program is initiated. Also like ''Chlamydomonas'', there are two "sexes", plus or minus controlled by a genes homologous to those found in ''

'' and ''

''.

References

External links

Gonium
- Description with pictures

- Research overview of Dr. Richard Michod at the University of Arizona who studies multicellular evolution and whose lab published a detailed phylogenetic tree of the

VIP
- The Volvocales Information Project led by Dr. Aurora M. Nedelcu at University of New Brunswick
Olson Lab
- Dr. Bradley Olson at Kansas State University who studies multicellular evolution with methods for growing Gonium

- Dr. Hisayoshi Nozaki at the University of Tokoyo who studies multicellular evolution and has cultured many

strains, including Gonium
Hallman Lab
- Dr. Armin Hallman at Bielefeld University whose lab developed a method for transforming Gonium *
UTEX
- The UTEX algal culture collection which houses many Gonium strains including pictures
CCAP
- The CCAP algal culture collection which houses many Gonium strains including pictures {{Taxonbar, from=Q310242 Chlamydomonadales genera Chlamydomonadales