Calyptogena magnifica (Fig.8), is a giant-sized mollusc (together with the mussel Bathymodiolus thermophiles), which is unusual for many bivalves of the deep-sea (Gage & Tyler 1991).
Figure 8. Calyptogena magnifica, Richard A. Lutz
C. magnifica may obtain a shell length of up to 26.3cm, and occurs in dense aggregations around hydrothermal vents (Gage & Tyler 1991), in the northern and southern East Pacific Rise and Galapagos Rift (Desbruyères et al. 2006; Pradillon & Gaill 2009).
This bivalve occurs only at hot vent sites, and it has been found that species distribution and abundance links with elevated H2S levels (Desbruyères et al. 2006; Pradillon & Gaill 2009).
Up to 75% of the gills in C. magnifica may be made up of incorporated symbiotic bacteria (Gage & Tyler 1991). In observations of C. magnifica at ‘Rose Garden on the Galapagos Rift’, H2S was found undetected around the siphons of C. magnifica; therefore it was concluded that these bivalves may gain energy by inserting their foot into crevices with an exposure to vent flow and they may also take up oxygen and inorganic carbon by means of their siphons and internal gill-structures (Gage & Tyler 1991; Hessler et al. 1988).
Bathymodiolus thermophilus (Fig.9), is distributed along the Galapagos Rift and East Pacific Rise (Desbruyères et al. 2006). It is a species endemic to hydrothermal vents and is commonly found in areas with ‘elevated temperatures and high levels of H2S’ (Desbruyères et al. 2006). The mussel may obtain a shell length of up to 18.4cm (Desbruyères et al. 2006; Fisher et al. 1988).
Figure 9. Bathymodiolus thermophilus, Woods Hole Oceanographic Institution
B. thermophilus has a fully-functional digestive system and may derive food particles from the water column, as well as ingest ‘free-living bacteria’ (Gage & Tyler 1991). The mussel also houses symbiotic bacteria within its gill-structures, but the exact role of these microorganisms is not fully known; however they may provide an additional source of energy. This may be why these mussels can cope with an extensive range of vent conditions and varying flow exposures (Fisher et al. 1988; Gage & Tyler 1991).