Monterey Bay Aquarium Research Institute
Marine Botany

Antithamnion defectum


The Antithamnion Genus was first discovered in 1847 by Nageli, and Antithamnion defectum was first discovered by Harald Kylin in 1925, 30-60 feet (9-18 meters) down on the pilings of the docks in Friday Harbor in the San Juan Islands, WA, USA. [1]

There were 51 identified species of Antithamnion in the world in 1989 [2], and my literature research indicates that there have been four more new species identified as of March 2005, making the total number of species 55. Since its discovery in 1947, a total of 100 species have been put in the genus, however 55 have been transferred to other genera, and at least 9 have been discovered to be conspecific with other Antithamnion species. [2] Over the last few decades, research has revealed that A. setaceum and A. pygmaeum are conspecific with A. defectum, and genetic analysis has revealed that A. defectum is closely related to A. sparsum and A. densum. [3]

Scroll down to learn more about the classification of Antithamnion defectum.

Division: Rhodophyta

The beautiful red algae! This Division is mostly marine algae with a wide variety of construction in forms, although most species are relatively small unlike the brown algae which include the well known kelps. There are over 4,000 known species and 675 genera. The red color of this algae comes from the photosynthetic phycobilin pigment, phycoerythrin. Some species are dominated by another pigment called phycocyanin, giving a more grayish-blue color. Chorophyll is used in photosynthesis as are carotenoid accessory pigments, and the main storage product is floridean starch. Most red algae have pit-plug-connections between cells and have cell walls made of cellulose, although the corallines use calcium carbonate. Red algae usually have three life stages, are dioecious, and have non-motile spores and sperm. [4]

Class: Florideophyceae

In this class, the thalli are multicellular, filamentous, polysiponous, or aggregated filaments which can appear more "leaf-like." Growth occurs from the apical cell, there are pit-connections, and both phycoerythrin and phycocyanin are present. Sexual reproduction is relatively typical of red algae (for more details see life-history link. [4]

Order: Ceramiales

Antithamnion sp. are part of this order because of their uniaxial, filamentous, growth. Filaments in this order all have an obvious apical cell(s) from which all of the growth occurs. Antithamnion defectum has cruciate division on its tetrasporangia, although other algae in the order may have tetrahedral division. [4]

Family Ceramiaceae

Antithamnion sp. are part of this family because of their uniaxial thalli and their lack of cortication. Other members of this family may be corticated to various extents, like Ceramium, and most members' reproductive structures lack any sterile covering. [4]

Genus: Antithamnion

This genus is characterized by verticillate branching, with the basal cell of each branchlet being smaller than adjacent cells. The tetrasporangia are lateral on the branchlets. [4]

Species: defectum

This species is special because the indeterminate branches lack an opposite whorl-branch. [1]

branching of A. defectum

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References and Acknowledgements

© 2005 Charlotte Stevenson

Last updated: Feb. 05, 2009