Alvinella pompejana

The family name Alvinellidae and genus name Alvinella both derive from DSV Alvin, the three-person submersible vehicle used during the discovery of hydrothermal vents and their fauna during the late 1970s. The family Alvinellidae contains over eight other species, but none matches the Pompeii worm's heat tolerance. The genus Alvinella also includes Alvinella caudata, the segmented worm. Pompeii worms get their specific name pompejana from the Roman city of Pompeii that was destroyed during an eruption of Mount Vesuvius in AD 79. ==Discovery==

In 1980 Daniel Desbruyères and Lucien Laubier, just a few years after the discovery of the first hydrothermal vent system, identified one of the most heat-tolerant animals on Earth — Alvinella pompejana, the Pompeii worm. It was described as a deep-sea polychaete that resides in tubes near hydrothermal vents, along the seafloor. In 1997, marine biologist Craig Cary and colleagues found the same worms in a new section of Pacific Ocean, near Costa Rica, also attached to hydrothermal vents. The new discovery and subsequent work led to important progress in the scientific knowledge of these special worms. == Description ==

Physiology Pompeii worms are usually around 10 cm in length, but can reach up to 13 cm. They have a diameter of less than 1 cm. with a red color due to their hemoglobin. The heart provides blood to these organs using contractions, pushing blood along the dorsal and ventral vessels. Beneath the heart lies the animal's stomach which connects to an oesophagus that is used to consume food. Finally, surrounding the organs is a coelom filled with coelomocytes, a type of phagocyte that acts as an immune system for the animal. Studies are hampered by the difficulties of sampling; It is currently quite difficult for Pompeii worms to survive decompression. Internal chemistry Alvinellidae have an exceptionally high congenital oxygen affinity, in addition to a high heat requirement for oxygenation (𝚫H). Therefore, to allow adequate release of oxygen within the body, the Pompeii worm has acidic blood with a pH range of 6.6-6.9. A lower pH decreases the energy required to unbind oxygen from hemoglobin by utilizing the Bohr effect. The effect gradually compounds as the hemoglobin's 4 O2 binding sites are emptied, and it is reaches its maximum when the hemoglobin is fully deoxygenated. As a result, they can release all possible oxygen without expending excessive energy. To further compound this effect, ''A. pompejana's'' vascular hemoglobin has a lower oxygen affinity when compared to coelomic hemoglobin. When it is time to rebind oxygen to the hemoglobin, the blood must be cooled to 20-30 °C to regain optimal cooperativity. However, hydrothermal vents reach much higher temperatures. This makes the low blood temperature strange and seemingly hard to maintain. The bacteria are known to live in a mutualistic relationship with A. pompejana, making them both symbiotrophs. The main nutrition for the Pompeii worm is derived from chemosynthetic bacteria, this is why it chooses to live in such intense environments. This is due to the toxic metal levels of hydrothermal vent fluid, a factor chemosynthetic bacteria require. Unfortunately, the low pH, low oxygen levels and aforementioned metals within the fluid create an environment only fit for extremophiles; A. pompejana has physiological traits to assist in combating this but they are not enough. As a result, they have developed a strong relationship with the bacteria. The bacteria detoxify the fluid; this allows the worm to feed and live. Then, as the worm lives it respires, thus giving the bacteria a carbon source to feed upon. As an additional benefit, the bacteria gain shelter and surfaces to multiply upon due to the worm's tubes. Living among Pompeii worms at the vents are several other polychaete species. They are found living near other alvinellids, polynoids, nereidids, and hesionids. Other taxa frequently found near them are amphipods and brachyuran crabs. Temperatures between 50 and 55 °C (122 to 131°F) for more than 2 hours was fatal for the Pompeii worms. The ideal temperature for the worms is between 20 and 42 °C (68 and 107.6 °F). Previous literature claimed that A. pompejana could thrive in temperatures up to 80 °C (176 °F). However, it was found that A. pompejana proteins started to denature at above 50 °C. This drastic change in literature is likely do to the fact that researchers previously punctured the worms to get a temperature reading inside, causing a change in the flow of water throughout the body of the worm and giving inaccurate results. The extreme thermal limit of A. pompejana is due to its internal chemistry. The proteins inside the Pompeii worm contain many small charged amino acids, which are hydrophobic. This helps the worm to regulate its temperature. A. pompejana also contains a large amount of collagen in its tissues. Collagen is the most heat resistant fiber and therefore allows the Pompeii worm to survive in these temperatures. It was found that the collagen in the Pompeii worm has high Proline concentration. Gly-X-Y triplets of the proline lead to a triple helical structure which greatly helped with stability. Proteins were less likely to be denatured at high temperatures due to this stability. The worm also uses tubes that surround it as a barrier to the hot water. Additionally, epibiotic bacteria coat the back of the worm and help protect from extreme temperatures. ==Biology==

Pompeii worms form large, aggregate colonies enclosed in long tubes. Attaching themselves to black smokers, the worms have been found to thrive at sustained temperatures of from and even for a short time, making the Pompeii worm the most heat-tolerant complex animal known to science after tardigrades (or water bears), which are able to survive temperatures over 150 °C. Pompeii worms simultaneously keep their heads (including the gills) in much cooler water while their tails are exposed to hot water. Since their internal temperature has yet to be measured, a Pompeii worm may survive exposure to hot water by dissipating heat through its head to keep its internal temperature within the realm previously known to be compatible with animal survival. The Pompeii worm feeds upon their chemosynthetic bacteria, using retractable, ciliated feeding tentacles to scoop them up or absorbing their organic matter within the hydrothermal vent fluid. These tentacles are coated with 4 types of secretory cells along the entire epidermis. The tentacle's muscle cells seem to be filled with homogenous blood cells and individual hat-shaped cells, the hat-shaped cells have a condensed nucleus and it is hypothesized that these are heavily modified sperm cells. Life cycle Alvinella pompejana are a gonochoric species with distinct differences between the male and female genital pores (located at the base of the gills). The current hypothesis for egg synthesis and spawning is as follows: first the yolk is formed through a long process within the animal's coelom, next, the mature eggs are stored and finally, the eggs are spawned when either an environmental or biological change occurs (eg. sperm transfer). The method for transfer of spermatozoa it is likely achieved through pseudo-copulatory behavior as the worms have been observed diving head-first into tubes in a display that may be mating. When it is deemed appropriate to fertilize the eggs they are seemingly selected based upon size and then individually passed through the spermathecae. This method of fertilization is more efficient than having all eggs be passed through at once. ==References==