Аннотация:The tubeworm Riftia pachyptila is a key primarily producer in the hydrothermal vent communities due to the symbiosis with sulphur-oxidizing bacteria, which provide nourishment to the worm from sulphide, oxygen, and carbon dioxide. These substances diffuse from the vent water into the worm’s blood through their tentacular crowns, and then to the bacteria, hosted in a specialised organ of the worm, called trophosome. The uptake rates of these substances depend on the surface/volume relationship of the tentacles. We here describe two morphotypes, “fat” and “slim”, respectively from the basalt sulphide-rich vents at 9°N and 21°N at the East Pacific Rise, and the highly sedimented, sulphide-poor vents at 27°N in the Guaymas basin. The “fat” morphotype has a thicker body, longer trunk, and smaller tentacular crowns, whereas the slim” morphotype has thinner body, shorter trunk, and presents longer tentacular crowns and higher number of tentacular lamellae. Given dependence on sulphide for the growth of R. pachyptila, as well as high genetic connectivity of the worm’s populations along the studied localities, we suggest that such morphological differences are adaptive and selected to keep the sulphide uptake near to the optimum values for the symbionts. “Fat” and “slim” morphotypes are also found in the vestimentiferan Ridgeia piscesae, in similar sulphide-rich and poor environments in the northern Pacific.