Codium Stackhouse, 1797

Holotype species: Codium tomentosum Stackhouse

Original publication and holotype designation: Stackhouse, J. (1797). Nereis britannica; continens species omnes fucorum in insulis britannicis crescentium: descriptione latine et anglico, necnon iconibus ad vivum depictis... Fasc. 2. pp. ix-xxiv, 31-70, pls IX-XIII. Bathoniae [Bath] & Londini [London]: S. Hazard; J. White.

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Description: Thallus spongy, anchored to rocks or shells by a weft of rhizoids, varying in size from 1 cm. to 10m. long. Habit varying widely applanate, pulvinate, digitaliform, globular, petaloid, membraniform, or dichotomously branched; erect or repent; branches wholly terete or variously flattened, at times anastomosing. Internal structure composed of a colorless medulla of densely intertwined siphons and a green palisade-like layer of vesicles called utricles. Organelles, including innumerable nuclei and discoid chloroplasts (but no amyloplasts) are confined to a layer of cytoplasm appressed to a wall of which mannan is an important constituent. Chloroplasts lack pyrenoids; carotenoid pigments include siphaxanthin and siphonein. Incomplete septa (plugs) formed by centripetal deposition of wall material. Utricles arise primarily by enlargement of sympodial branches of medullary siphons, secondarily by budding or by production of additional utricle-forming medullary siphons from basal portion of existing utricles. Mature utricles cylindrical or clavate, the apical wall usually thickened and often ornamented in a pattern characteristic of particular species. Rhizoidal siphons, which become buried in the medulla, also produced from basal portion of utricles. Colorless hairs, each with a basal plug, produced by utricles shortly below their apices, caducous at the plug, which remains as a prominent scar. Gametangia produced laterally by utricles, each with a basal plug above a short pedicel; fusiform to ovoid, the contents cleaving into biflagellate gametes following meiosis. Gametes extruded in a gelatinous mass through apical rupture. Male gametes contain only one or two chloroplasts, female gametes several times larger, with numerous chloroplasts, the two types produced on the same thallus (monoecious) or more often on different thalli (dioecious). Zygote develops into amorphous prostrate vesicle that produces erect elongate vesicles; these in turn initiate primary utricle-producing siphons which eventually consolidate into a multiaxial thallus. Asexual reproduction by parthenogenesis, fragmentation, or the cutting off of modified aborted gametangia. Despite the ubiquity of Codium very little is know about its biology. The life history outlined above is generalized from fragmentary studies.

Information contributed by: P. C. Silva. The most recent alteration to this page was made on 2011-08-29 by M.D. Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Gender: This genus name is currently treated as neuter.

Comments: Because of its ready availability throughout the world, Codium is often included in comparative biochemical and physiological studies, resulting in many unconsolidated data. Codium fragile subsp. tomentosoides, a weedy genotype of a highly variable and complex species that has spread widely in the Pacific and Atlantic Oceans, has evoked some attention because of its obvious effect on newly invaded biotas. Form/function studies have been made on the preceding species and on C. decorticatum which is widespread in warm Atlantic waters. Although it is assumed that Codium is diploid, C. fragile subsp. tomentosoides has been shown to be haploid but to have a DNA content equivalent to a tetraploid. Chromosome numbers are known for only six species; the basic haploid number appears to be 10. The firm apical walls that form the surface of the thallus, together with the interstices in the cortex make Codium an excellent host for numerous small algae such as Ectocarpus, Streblonema and Ceramium. In a curious biotic interrelationship, chloroplasts of Codium are ingested by some sea slugs (sacoglossan opisthobranchs), which use the photosynthetic products of these endosymbiotic organelles to synthesize mucopolysaccharides. Most of the species have narrow geographic ranges and exhibit little morphological variability. A few species range widely and exhibit complex patterns of morphological variability. Codium fragile has become cosmopolitan by the spreading of weedy genotypes, most notably subsp. tomentosoides ("oyster thief"). Codium grows intertidally, and to at least -40m. It occurs in all marine waters except the Arctic and Southern Oceans. The largest numbers of species are found in floras that are transitional between temperate and subtropical, namely Japan (19), South Africa (19), Australia (l8), and California-Mexico (12). Each of these floras includes a member of most sections of the genus, indicating an ancient dispersal of the progenitors. Because of lack of calcification, there is no fossil record of the genus.

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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.

Linking to this page: https://www.algaebase.org/search/genus/detail/?genus_id=39

Citing AlgaeBase
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 29 August 2011. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 18 April 2024

 
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