Giant tube worm
Giant tube worms, Riftia pachyptila, are marine invertebrates in the phylum Annelida (formerly grouped in phylum Pogonophora and Vestimentifera) related to tubeworms commonly found in the intertidal and pelagic zones. Riftia pachyptila lives over a mile deep and up to several miles deep on the floor of the Pacific Ocean near black smokers and can tolerate extremely high temperatures and sulfur levels. They can reach a length of 2.4 m (7 ft 10 in).
They have a highly vascularized, red "plume" at the tip of their free end which is an organ for exchanging compounds with the environment (e.g., H2S, CO2, O2, etc). The tube worm does not have many predators, as few creatures live on the sea bottom at such depths. If threatened, the plume may be retracted into the worm's protective tube. The plume provides essential nutrients to bacteria living inside a specialized organ within its body (i.e., trophosome) as part of a symbiotic relationship. They are remarkable in that they have no digestive tract, but the bacteria (which may make up half of a worm's body weight) turn oxygen, hydrogen sulfide, carbon dioxide, etc. into organic molecules on which their host worms feed. This process, known as chemosynthesis, was first recognized by Colleen Cavanaugh while she was a graduate student at Harvard. With sunlight not available as a form of energy, the tubeworms rely on bacteria in their habitat to obtain nutrients.
The bright red color of the plume structures results from several extraordinarily complex hemoglobins found in them, which contain 24 or 144 globin chains (presumably each including associated heme structures). These tube worm hemoglobins are remarkable for carrying oxygen in the presence of sulfide, without being completely "poisoned" or inhibited by this molecule, as hemoglobins in most other species are.
To reproduce, Riftia pachyptila females release lipid-rich eggs into the surrounding water so they start to float upwards. The males then unleash sperm bundles that swim to meet the eggs. After the eggs are fertilized, the larvae swim down to attach themselves to the rock.
Riftia pachyptila has the fastest growth rate of any known marine invertebrate. These organisms have been known to colonize a new site, grow to sexual maturity and increase in length to 4.9 feet (1.5 m) in less than two years. This is in sharp contrast to Lamellibrachia luymesi, the tube worms that live at deep sea cold seeps and grow very slowly for most of their lives. It takes from 170 to 250 years for Lamellibrachia luymesi to grow 2 meters in length, and even longer worms have been discovered.
- ^ Ruppert, E.; Fox, R.; Barnes, R. (2007). Invertebrate Zoology: A functional Evolutionary Approach (7th ed.). Belmont: Thomson Learning. ISBN 0030259827.
- ^ Cavanaugh, Colleen M.; et al. (1981). "Prokaryotic Cells in the Hydrothermal Vent Tube Worm Riftia pachyptila Jones: Possible Chemoautotrophic Symbionts". Science 213 (4505): 340–342. doi:10.1126/science.213.4505.340. PMID 17819907.
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- ^ http://www.sciencedaily.com/releases/2000/02/000203075002.htm
- Minic, Zoran; Hervé, Guy (2004). "Biochemical and enzymological aspects of the symbiosis between the deep-sea tubeworm Riftia pachyptila and its bacterial endosymbiont". European Journal of Biochemistry 271 (15): 3093–3102. doi:10.1111/j.1432-1033.2004.04248.x.
- Zal, Franck; et al. (1996). "The Multi-hemoglobin System of the Hydrothermal Vent Tube Worm Riftia pachyptila: II. Complete polypeptide chain composition investigated by maximum entropy analysis of mass spectra". Journal of Biological Chemistry 271 (15): 8875–8881. doi:10.1074/jbc.271.15.8875. PMID 8621529. http://www.jbc.org/cgi/content/abstract/271/15/8875.