by Piter Kehoma Boll
Let’s dive deep into the ocean and talk about this awesome animal, the giant tube worm Riftia pachyptila. Initially classified in a separate phylum, Vestimentifera, today it is included in a family of Annelids called Sibloginidae. Its common name comes from the fact that it can reach a length of 2.4 meters, quite big for a worm.
Endemic to deep-sea hydrothermal areas in the Pacific ocean, these worms are adapted to tolerate the high temperatures, pressure and levels of hydrogen sulfide in their environments. With their body protected by a chitin tube which can reach 3 meters in length, the only part exposed is a red structure, the branchial plume, highly vascularized ad rich in a hemoglobin complex of high molecular mass.
Below the plume lies the vestimentum, a muscular region which hosts the brain and the heart and is responsible for the extension and withdrawal of the plume. The name of the old phylum comprising this species, Vestimentifera, refers to this structure.
Follwing the vestimentum is the trunk and after it the opisthosome, which anchors the animal to the tube.
The plume is used to carry oxygen, carbon dioxide and sulfides into the animal’s body, which, however, lacks a mouth and gut.
To achieve nutrients, the giant tube worms host an endosymbiotic chemolithoautotrophic γ-Proteobacterium inside the trophosome, a richly vascularized organ in the trunk that constitutes a specific morphological adaptation to house the symbiotic bacteria. The sulfides are transported by the worm from the environment to the symbionts, which possess a sulfur oxidizing respiratory system and so can produce metabolic energy for themselves and for the worm.
The association between the giant tube worm and its chemoautrophic bacteria was the first of this kind to be described more than 30 years ago by Cavanaugh et al. and is currently the best studied one, but many questions about the details of this relationship, including the achievement of the bacteria by young worms, are yet to be fully answered.
Since the worm lacks a digestive system, its nutrition is entirely dependent on its symbiotic bacteria and all the anatomic adaptations designed to allow this association makes this a very good example of coevolution and make us think that there are no limits for life to adapt itself.
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Lopez-Garcia, P., Gaill, F., & Moreira, D. (2002). Wide bacterial diversity associated with tubes of the vent worm Riftia pachyptila. Environmental Microbiology, 4 (4), 204-215 DOI: 10.1046/j.1462-2920.2002.00286.x
Minic, Z., & Hervé, G. 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
Stewart FJ, & Cavanaugh CM 2006. Symbiosis of thioautotrophic bacteria with Riftia pachyptila. Progress in molecular and subcellular biology, 41, 197-225 PMID: 16623395