Volvox Linnaeus, 1758: 820

Classification:
Empire Eukaryota
Kingdom Plantae
Subkingdom Viridaeplantae
Phylum Chlorophycophyta
Class Chlorophyceae
Order Volvocales
Family Volvocaceae

Lectotype species: Volvox aureus Ehrenberg

Original publication: Linnaeus, C. (1758). Systema naturae per regna tria naturae, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. Vol. 1 pp. [i-iv], [1]-823. Stockholmiae [Stockholm]: impensis direct. Laurentii Salvii.

Type designated in Ehrenberg, C.G. (1838). Infusionsthierchen als vollkommene Organismen. I-II. pp. 1-547, 64 pls.. Leipzig: Leopold Voss.

Taxonomic status: currently recognized as a distinct genus.

Description: Colonies spherical, subspherical, ellipsoidal or ovoid, containing 500-50,000 cells arranged at the periphery of a gelatinous matrix, forming a hollow sphere. Two to 50 large reproductive cells (gonidia) situated in posterior 1/2 to 2/3 of colony. Each cell enclosed by gelatinous sheath which is distinct or confluent (species dependent). Somatic cells spherical, ovoid or star-shaped, each with two equal flagella, a stigma, two contractile vacuoles at base of flagella, and a cup-shaped chloroplast with single pyrenoid. Cytoplasmic strands between cells are thick, thin or absent and this is species dependent. Asexual reproduction by autocolony formation, each reproductive cell dividing successively to form a hollow, spheroidal plakea, which then inverts to form a daughter colony. Sexual reproduction oogamous; in monoecious species the sexual colony with both sperm packets (bundles of sperm) and eggs. In dioecious species, male colonies with androgonidia which divide successively into sperm packets; such males may be markedly reduced in size (dwarf male) or nearly as large as asexual colonies. The female colony has eggs, whose number is nearly the same as that of gonidia in asexual colonies (facultative female) or much larger (special female). After fertilization zygotes develop a heavy cell wall that may be ornamented with reticulation or spines. Upon germination, zygotes produce a single biflagellate gone cell. Volvox is cosmopolitan in freshwater; V. aureus is common. Volvox was established with V. globator and more than 12 additional species have been described. The genera Besseyosphaera, Campbellosphaera, Merrillosphaera, Copelandosphaera and Janetosphaera were described by Shaw but are now included in Volvox. Each of these genera was later considered to be a section of Volvox, with Euvolvox [=Volvox] including species referable to Volvox by Shaw. Later, the sections Campbellosphaera and Besseyosphaera were rejected and 18 species were recognized in four sections based on differences in the gelatinous matrix, shape of somatic cells, and cytoplasmic strands connecting cells in the colony. Embryogenesis of V. carteri has been studied in detail, and chemical induction of sexual colonies were described for V. aureus, V. carteri, V. rousseletii, V. gigas, V. observus and V. capensis. Inducers are species-specific glycoproteins of ca. 30,000 MW produced by sperm, except in V. capensis where L-glutamic acid is reported. Ultrastructure of flagellar apparatuses in V. rousseletii and V. carteri implied a remote relationship. The extracellular matrix of the four sections of Volvox has also been studied ultrastructurally, and a system of nomenclature was proposed in which the matrix was divided into four main zones.

NCBI Nucleotide Sequences

Numbers of names and species: There are 133 species (and infraspecific) names in the database at present, of which 17 have been flagged as currently accepted taxonomically.

Names: ('C' indicates a name that is currently accepted taxonomically; 'S' a homotypic or heterotypic synonym; 'U' indicates a name of uncertain taxonomic status, but which has been subjected to some verification nomenclaturally; 'P' indicates a preliminary AlgaeBase entry that has not been subjected to any kind of verification. For more information on a species click on it to activate a link to the Species database):

References
Janet, C. (1922). Le Volvox. Deuxième mémoire. Paris : 1-66, pls 1-4.

Information contributed by: H. Nozaki. The most recent alteration to this page was made on 17 Oct 2009 by Stephen Cusack.

Contributors
Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.

Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.