Giant tube worms,
Riftia pachyptila, are
marineAn ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
invertebrateAn invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s in the phylum
AnnelidThe annelids , formally called Annelida , are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches...
a (formerly grouped in phylum
PogonophoraThere are two taxa with the name Pogonophora:*Pogonophora - an obsolete animal phylum, now treated as part of the family Siboglinidae*Pogonophora - a genus in the Euphorbiaceae...
and Vestimentifera) related to tube worms commonly found in the intertidal and
pelagic zoneAny water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
s.
Riftia pachyptila lives over a mile deep and up to several miles deep on the floor of the
Pacific OceanThe Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
near black smokers and can tolerate extremely high
hydrogen sulfideHydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
levels. They can reach a length of 2.4 metre.
Body structure
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.,
H2SHydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
,
CO2Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
,
O2Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, 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
bacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
living inside a specialized organ within its body (i.e.,
trophosomeTrophosome is an organ found in the coelomic cavity of the giant tube worm, Riftia pachyptila. Symbiotic bacteria in the trophosome oxidize sulfur found in the tube worm's environment and produce organic molecules that the worm can use as an energy source. This process is known as chemosynthesis....
) 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
oxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
,
hydrogen sulfideHydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
,
carbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, etc. into organic molecules on which their host worms feed. This process, known as
chemosynthesisIn biochemistry, chemosynthesis is the biological conversion of one or more carbon molecules and nutrients into organic matter using the oxidation of inorganic molecules or methane as a source of energy, rather than sunlight, as in photosynthesis...
, was first recognized by
Colleen CavanaughColleen Cavanaugh, Ph.D., is a microbiologist and Edward C. Jeffrey Professor of Biology at Harvard University who has studied hydrothermal vent ecosystems for over 20 years. As a graduate student, Cavanaugh was the first to propose that the giant tube worm, Riftia pachyptila, obtains its food...
while she was a graduate student.
The bright red color of the plume structures results from several extraordinarily complex
hemoglobinHemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
s found in them, which contain up to 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.
Nitrate and nitrite are toxic but nitrogen is required for biosynthetic processes. The chemosynthetic bacteria within the trophosome are able to convert this nitrate to
ammoniumThe ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
ions, which then are available for production of amino acids in the bacteria, which are in turn released to the tube worm. In order to transport nitrate to the bacteria,
R. pachyptila are able to concentrate nitrate in their blood to a concentration that is 100 times more concentrated than the surrounding water. The exact mechanism of
R. pachyptila’s ability to withstand and concentrate nitrate is still unknown.
Energy and nutrient source
With sunlight not available directly as a form of energy, the tubeworms rely on bacteria in their habitat to oxidize hydrogen sulfide, using dissolved oxygen in the water for respiration. They use this reaction for energy in 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 tubeworms are similar to many forms of life which live in the ocean below depths that sunlight can penetrate. However, tubeworms are unique as a large animal, in being able to use bacteria to indirectly obtain all materials they need for growth, from extremely small molecules dissolved in 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. This is in sharp contrast to
LamellibrachiaLamellibrachia is a genus of tube worms related to the giant tube worm, Riftia pachyptila. It lives at deep-sea cold seeps where hydrocarbons are leaking out of the seafloor. It is entirely reliant on internal, sulfide-oxidizing bacterial symbionts for its nutrition.L...
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.
See also
- Siboglinidae
Siboglinidae, also known as the beard worms, is a family of polychaete annelid worms whose members made up the former phyla Pogonophora and Vestimentifera. They are composed of about 100 species of vermiform creatures and live in thin tubes buried in sediments at ocean depths from 100 to 10,000 m...
- Lamellibrachia
Lamellibrachia is a genus of tube worms related to the giant tube worm, Riftia pachyptila. It lives at deep-sea cold seeps where hydrocarbons are leaking out of the seafloor. It is entirely reliant on internal, sulfide-oxidizing bacterial symbionts for its nutrition.L...
- List of long-living organisms
- Maximum life span
Maximum life span is a measure of the maximum amount of time one or more members of a population has been observed to survive between birth and death.Most living species have at least one upper limit on the number of times cells can divide...
- Pompeii worm
Alvinella pompejana, , is a species of deep-sea polychaete worm...
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