Giant tube worm

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Giant tube worm

Scientific classification

Kingdom:	Animalia
Phylum:	Annelida
Class:	Polychaeta
Family:	Siboglinidae
Genus:	Riftia
Species:	R. pachyptila

Binomial name

Riftia pachyptila
M. L. Jones, 1981

Giant tube worms are marine invertebrates in the phylum Vestimentifera (formerly grouped in phylum Pogonophora) related to tubeworms commonly found in the intertidal and pelagic zones. Riftia pachpieptila lives over a mile deep on the floor of the Pacific Ocean near black smokers and can tolerate extremely high temperatures and sulfur levels. They can grow up to a length of eight feet (2.4 meters).

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 any, for few creatures live on the sea bottom. but 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 their 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 was first recognized by Colleen Cavanaugh while she was a graduate student at Harvard.^{[citation needed]}This evolutionary adaptation presumably came about due to the fact that the worms live so far away from sunlight. With sun 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 being able to carry oxygen in the presence of sulfide, and indeed to also carry sulfide, without being completely "poisoned" or inhibited by this molecule, as hemoglobins in most other species are.