A. pompejana (Fig.7), is found in the East Pacific Rise, but not in the Guaymas Basin and Galapagos Rift, unlike R. pachyptila (Desbruyères et al. 2006).
Figure 7. Alvinella pompejana (Pompeii worm), University of Delaware College of Marine Studies.
This worm has been described as being amongst the most heat-tolerant eukaryotic, metazoan organisms on the planet (Pradillon & Gaill 2009), as it has been shown to inhabit the surfaces of very high temperature vent chimneys, that may reach 80°C or more; such as the surfaces of the black-smoker chimneys of the Eastern-Pacific Rise (Pradillon & Gaill 2009). For this reason, A. pompejana is a much studied species for the adaptive mechanisms it uses to cope with high environmental temperatures (Pradillon & Gaill 2009).
A. pompejana may grow up to 150mm in length and lives in a tube, which typically forms honey-comb arrangements with other worms of the species, around the openings of vents and on the walls of sulphide chimneys (Desbruyères et al. 2006; Gage & Tyler 1991; Pradillon & Gaill 2009).
In contrast to R. pachyptila; A. pompejana possesses ‘epibiotic-chemoautotrophic symbionts’. These are abundant on the surface of the branched appendages of the worm; they are also found on the inner surface of the tube which it inhabits (Desbruyères et al. 2006; Gage & Tyler 1991; Pradillon & Gaill 2009).
The role of the symbiotic bacteria is not fully understood and could be important for helping to provide a source of nutrition for the worm by production of organic compounds (Desbruyères et al. 2006; Gage & Tyler 1991; Pradillon & Gaill 2009); or to reduce the toxicity of the surrounding environment (Gage & Tyler 1991; Pradillon & Gaill 2009). They may also help to reduce the extent of heat exposure from the sulphide chimneys on which it lives (Pradillon & Gaill 2009).
The way in which these worms tolerate such high temperatures may be due to their extracellular composition which contains modified collagen, that allows for an exceeded thermal stability, withstanding temperatures of over 65°C (Pradillon & Gaill 2009).
However, unlike adult worms, which inhabit hot, sulphide-chimney walls, embryonic worms do not possess forms of collagen that allow them to be thermotolerant (Pradillon & Gaill 2009). A study showed that embryos incubated near to adult worms, in hot venting areas, showed development-prevention or death (Pradillon & Gaill 2009). Nevertheless, embryos that were incubated near to the milder, R. pachyptila region, below the A. pompejana colony, survived and developed normally(Pradillon & Gaill 2009).
These results suggest that development of juvenile A. pompejana species can occur outside of the main colony until the worms are developed enough to withstand the high-temperature habitat of the adult worms (Pradillon & Gaill 2009).
It has also been shown that development of the worms is halted at ‘abyssal temperatures’ of approximately 2°C, such as those in bottom currents near to the sea bed. These currents may allow for ‘dispersal of the embryos in a dormant state’, which could then be reversed when the embryos encountered a vent-site, where they would experience an increase in temperature; however more research into this theory is needed (Pradillon & Gaill 2009).