Giant tube worm

Not to be confused with Giant tube worm (shipworm).
Giant tube worms
Scientific classification
Kingdom: Animalia
Phylum: Annelida
Class: Polychaeta
Order: Canalipalpata
Family: Siboglinidae
Genus: Riftia
Species: R. pachyptila
Binomial name
Riftia pachyptila
M. L. Jones, 1981

Giant tube worms, Riftia pachyptila, are marine invertebrates in the phylum Annelida[1] (formerly grouped in phylum Pogonophora and Vestimentifera) related to tube worms commonly found in the intertidal and pelagic zones. Riftia pachyptila live 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 hydrogen sulfide levels. These worms can reach a length of 2.4 m (7 ft 10 in) and their tubular bodies have a diameter of 4 cm (1.6 in). Ambient temperature in their natural environment ranges from 2 to 30 degrees Celsius.[2]

The common name "giant tube worm" is however also applied to the largest living species of shipworm, Kuphus polythalamia, which despite the name "worm" is a bivalve mollusc, rather than an annelid.

Development

Riftia develop from a free-swimming, pelagic, non-symbiotic trochophore larva, which enters juvenile (metatrochophore) development, becoming sessile and subsequently acquiring symbiotic bacteria.[3][4] The symbiotic bacteria, on which adult worms depend for sustenance, are not present in the gametes, but are acquired from the environment via the digestive tract. The digestive tract transiently connects from a mouth at the tip of the ventral medial process to a foregut, midgut, hindgut and anus. After symbionts are established in the midgut, it undergoes substantial remodelling and enlargement to become the trophosome, while the remainder of the digestive tract has not been detected in adult specimens.[5]

Body structure

Hydrothermal vent tubeworms get organic compounds from bacteria that live in their trophosome.

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. If threatened, the plume may be retracted into the worm's protective tube. The plume provides essential nutrients to bacteria living inside the trophosome. Tube worms have no digestive tract, but the bacteria (which may make up half of a worm's body weight) convert oxygen, hydrogen sulfide, carbon dioxide, etc. into organic molecules on which their host worms feed. This process, known as chemosynthesis, was recognized within the trophosome by Colleen Cavanaugh.[6]

The bright red color of the plume structures results from several extraordinarily complex hemoglobins, which contain up to 144 globin chains (each presumably including associated heme structures). These tube worm hemoglobins are remarkable for carrying oxygen in the presence of sulfide, without being inhibited by this molecule as hemoglobins in most other species are.[7][8]

Nitrate and nitrite are toxic, but nitrogen is required for biosynthetic processes. The chemosynthetic bacteria within the trophosome convert this nitrate to ammonium ions, which then are available for production of amino acids in the bacteria, which are in turn released to the tube worm. To transport nitrate to the bacteria, R. pachyptila concentrate nitrate in their blood, to a concentration 100 times more concentrated than the surrounding water. The exact mechanism of R. pachyptila’s ability to withstand and concentrate nitrate is still unknown.[9]

Energy and nutrient source

With sunlight not available directly as a form of energy, the tube worms rely on bacteria in their habitat to oxidize hydrogen sulfide,[10] using dissolved oxygen in the water as electron acceptor. This reaction provides the energy needed for chemosynthesis. For this reason, tube worms are partially dependent on sunlight as an energy source, since they use free oxygen, which has been liberated by photosynthesis in water layers far above, to obtain nutrients. In this way tube worms are similar to many forms of life which live in the ocean below depths that sunlight can penetrate. However, tube worms are unique in being able to use bacteria to indirectly obtain almost all materials they need for growth from molecules dissolved in water. Some nutrients have to be filtered out of the water. Tube worm growth resembles that of hydroponically grown fungi more than it does that of typical animals which need to "eat".

Reproduction

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 have hatched, the larvae swim down to attach themselves to the rock.

Growth rate and age

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.[11] 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.[12]

See also

References

  1. ↑ Ruppert, E.; Fox, R.; Barnes, R. (2007). Invertebrate Zoology: A functional Evolutionary Approach (7th ed.). Belmont: Thomson Learning. ISBN 0-03-025982-7.
  2. ↑ Bright, M.; Lallier, F. H. (2010). "The biology of vestimentiferan tubeworms" (PDF). Oceanography and Marine Biology: An Annual Review. Taylor & Francis. 48: 213–266. doi:10.1201/ebk1439821169-c4. Retrieved 2013-10-30.
  3. ↑ Monica Bright. "Riftia pachyptila".
  4. ↑ Diane K. Adams; et al. (Mar 2012). "Larval dispersal: Vent life in the ocean column" (PDF). Oceanography.
  5. ↑ Meredith L. Jones; Stephen L. Gardiner (Oct 1989). "On the early development of the vestimentiferan tube worm Ridgeia sp. and Observations on the Nervous System and Trophosome of Ridgeia sp. and Riftia pachyptila" (PDF). Biol Bull. pp. 254–276.
  6. ↑ 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.
  7. ↑ Zal F, Lallier FH, Green BN, Vinogradov SN, Toulmond A (Apr 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" (Free full text). J. Biol. Chem. 271 (15): 8875–81. doi:10.1074/jbc.271.15.8875. ISSN 0021-9258. PMID 8621529.
  8. ↑ Minic Z, Hervé G (Aug 2004). "Biochemical and enzymological aspects of the symbiosis between the deep-sea tubeworm Riftia pachyptila and its bacterial endosymbiont". Eur. J. Biochem. (Free full text). 271 (15): 3093–102. doi:10.1111/j.1432-1033.2004.04248.x. ISSN 0014-2956. PMID 15265029.
  9. ↑ Edda Hahlbeck; Mark A. Pospesel; Franck Zal; James Childress; Horst Felbeck (July 2005). "Proposed nitrate binding by hemoglobin in Riftia pachyptila" (Free full text). Deep-Sea Research. 52 (10): 1885–1895. doi:10.1016/j.dsr.2004.12.011. ISSN 0967-0637.
  10. ↑ C.Michael Hogan. 2011. Sulfur. Encyclopedia of Earth, eds. A.Jorgensen and C.J.Cleveland, National Council for Science and the environment, Washington DC
  11. ↑ Lutz, R. A.; Shank, T. M.; Fornari, D. J.; Haymon, R. M.; Lilley, M. D.; Von Damm, K. L.; Desbruyeres, D. (1994). "Rapid growth at deep-sea vents". Nature. 371 (6499): 663. doi:10.1038/371663a0.
  12. ↑ "Tube Worms In Deep Sea Discovered To Have Record Long Life Spans". ScienceDaily.
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