R. pachyptila, (Fig.5), is known to be distributed along the Galapagos Rift and East Pacific Rise including the Guaymas Basin (Desbruyères et al. 2006).
Figure 5. Riftia pachyptila, C. Van Dover (OAR/National Undersea Research Program (NURP)
These worms may grow up to 1.5m in length, possessing tubes made from chitin-protein, that form permanent attachment to sulphide chimneys (Fig.5) (Desbruyères et al. 2006; Gage & Tyler 1991). They are the fastest-growing vestimentiferans described to date (Desbruyères et al. 2006; Gage & Tyler 1991; Tait & Dipper 1998).
Describing R. pachyptila in taxonomic terms was at first difficult, due to its novel anatomical features and morphology, namely having no digestive system or particulate feeding mechanisms (Gage & Tyler 1991; Tait & Dipper 1998), therefore, it was placed into a new family, Riftiidae (Gage & Tyler 1991).
These worms settle in areas with a flow of sulphide-enriched warm water with which they engage with their red plume to supply their symbiotic bacteria with H2S. They possess haemoglobin in their red plume (Fig.6) which enables them to cope lengthy anoxic periods (Gage & Tyler 1991).
Figure 6. Riftia pachyptila cross-section, David Fischer.
The chemoautotrophic system used by the endosymbionts of R. pachyptila is amongst one of the most studied. These chemoautotrophic bacteria live within the specialised cells of the trophosome (Fig.6), which is a tissue that can oxidize H2S (Gage & Tyler 1991; Pradillon & Gaill 2009).