''Proterospongia'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of single-celled aquatic organisms which form

colonies In modern parlance, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the '' metropolitan state'' ...

. It belongs to the

choanoflagellate The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals. Choanoflagellates are collared flagellates, having a funnel shaped collar of interconne ...

class. As a colony-forming choanoflagellate, ''Proterospongia'' is of interest to scientists studying the mechanisms of intercellular signaling and adhesion present before animals appeared. King, N. The Unicellular Ancestry of Animal Development. Developmental Cell (2004) 7:313-325King, N. and S. B. Carroll. 2001. A receptor tyrosine kinase from choanoflagellates: molecular insights into early animal evolution. Proc Natl Acad Sci U S A 98:15032-7.

Physical characteristics

Members of ''Proterospongia'' have the typical choanoflagellate cell structure characterized by a cell body 5-10μm in diameter with a 20-30μm apical

flagellum A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

surrounded by a collar of 15-25 actin-filled

microvilli Microvilli (singular: microvillus) are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, and are involved in a wide variety of functions, including absorption, secretion, ...

.Leadbeater, B.S.C.; Thomsen H.A. Order Choanoflagellida. The Illustrated Guide to the Protozoa, second edition, (2000) pp. 14-37.Leadbeater, B.S.C. Life-History and Ultrastructure of a New Marine Species of ''Proterospongia'' (choanoflagellida). J. mar. biol. Ass. U.K. (1983) 135-160 The flagellum propels swimming cells through the water column and creates water currents through the microvilli, which trap foodstuff such as bacteria and detritus. The arrangement of organelles in ''Proterospongia'' appears consistent with other choanoflagellates and is characterized by an anterior dictyosome under the flagellar base, a central nucleus, peripheral mitochondria and a posterior food vacuole. As a member of the

Codonosigidae Codonosigidae were a Choanoflagellate The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals. Choanoflagellates are collared flagellates, hav ...

family, ''Proterospongia'' have only a fine investment that is indistinct by light microscopy or completely lack an outer-covering. ''Proterospongia'' species are distinguished by colony morphology, which vary from simple chains of cells to striking astral assemblages.Kent, W.S. Manual of the Infusoria (1880-1882) Colonies having extracellular jelly or mucilage have been described by Kent, Lackey, and Leadbeater; however the composition of this substance is unknown.Lackey, J.B. Morphology and Biology of a Species of ''Proterospongia''. Trans. Amer. Micro. Soc. (1959) pp. 202-206. Kent also described a ''Proterospongia'' species containing two types of cells embedded in mucilage; however, this is the only account of such a species and it has been suggested that the observed amoeboid cells were actually posterior tentacles that are present on some choanoflagellates.

Life history

Although several ''Proterospongia''

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

have been described, only ''P. choanojuncta'' has a described life history. Based on this description, ''Proterospongia'' alternates between colonial and swimming and adherent solitary states. Leadbeater’s 1983 description resulted in the consolidation of ''Choanocea perplexea'' and ''Proterospongia choanojuncta'' species into ''Proterospongia choanojuncta''. Additional studies of solitary and colonial species may result in further species consolidation.

Classification

''Proterospongia'' is a taxonomic classification of colonial Codonosigidae choanoflagellates based on the physical appearance of individual cells and the morphology of the colony. First described by Kent in ''Manual of the Infusoria (1880-1882)'', there are six described species of ''Proterospongia'' and the colony structure varies between species. The members of ''Proterospongia''

remain to be classified in a phylogenetic framework.

Citations

Additional references

# # James, T. Y., F. Kauff, C. L. Schoch, et al. mult. 2006. Reconstructing the early evolution of Fungi using a six-gene phylogeny. Nature 443:818-22. # Lang, B. F., C. O'Kelly, T. Nerad, M. W. Gray, and G. Burger. 2002. The closest unicellular relatives of animals. Curr Biol 12:1773-8. # Philippe, H, Snell, EA, Bapteste, E, Lopez, P, Holland, PWH, and D Casane. 2004. Phylogenomics of eukaryotes: the impact of missing data on alignments. Molecular Biology and Evolution. 21(9):123-135. # Snell, EA, Furlong, RF, and PWH Holland. 2001. Hsp70 sequences indicate that choanoflagellates are closely related to animals. Current Biology. 11:967-970.

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