The small species of Pogonophora that are widely distributed in sediments along the Continental Slope and in the Norwegian fjords (Webb, 1965; Southward & Southward, 1967; Southward, 1971,1979) carry Gram-negative bacteria in the posterior part of the body (Southward, 1982). In this they resemble the giant pogonophores (Vestimentifera) that live around hydrothermal vents in the Pacific ocean floor (Cavanaugh et al. 1981; Cavanaugh, 1983). The bacteria in both groups are autotrophic (Felbeck, 1981; Southward et al. 1981), capable of synthesizing organic matter from carbon dioxide. The bacteria in Riftia and other vent pogonophores appear to obtain energy by oxidation of reduced sulphur compounds (Felbeck, 1981; Felbeck, Childress & Somero, 1981). Hydrothermal vent waters may contain as much as 6 nut dissolved sulphide (Edmond et al. 1982; Edmond & Von Damm, 1983), which is diluted to about 200-300 μM near the giant pogonophores, whose blood can transport sulphide without affecting the affinity of its haemoglobin for oxygen (Arp & Childress, 1983; Powell & Somero, 1983; Childress, Arp & Fisher, 1984).