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The "green sea fingers" characteristic of the green alga Codium fragile also give rise to another apt description as "dead man's fingers", because the tubular structures tend to hang from rocks when the tide is low. This common species is a dark green filamentous alga that inhabits the intertidal zone, and is a member of the family Codiaceae, lacking leukoplasts and pyrenoids and having variable thallic forms.

Most specimens range from 10 to 30 centimeters in length, and have several branches that spawn from a broad basal disk. The club-shaped utricles, illustrated in the digital image above, are filled with chloroplasts (the site of photosynthesis for these sea creatures), and are tiny woven filaments that comprise the mature diploid macrothallus. The utricles contain chambers, termed gametangia, which undergo meiosis to generate and store biflagellated haploid gametes. Reproduction is triggered by exposure to light and tides, and occurs throughout the year. The female gamete is about twice the size of its male counterpart, but both have an eyespot to sense light and direct them to rise to the surface of the sea for fertilization. After the gametes fuse, they create a diploid zygote that forms a coenocyte after repeated cytokinetic mitotic chromosome divisions.

Contributing Authors

Cynthia D. Kelly, Thomas J. Fellers and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.



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