Meeting Abstract
The iconic ‘scaly-foot gastropod’ from deep-sea hydrothermal vent ecosystems of the Indian Ocean is distinctive for the dermal scales covering its foot. These iron-sulfide coated sclerites, and its nutritional dependence on endosymbiotic bacteria, are both noted as specialist adaptations to the ‘extreme’ environment of hydrothermal vents. The distinctive scales are reminiscent of the girdle scales in polyplacophoran molluscs (chitons) and the multipart scleritomes of many early fossil molluscs. Despite striking external similarities, the sclerites and chiton scales are secreted by starkly different mechanisms. This convergence highlights the ability of molluscs to rapidly adapt mineralised dermal structures. We also present new evidence for further specialist adaptations revealed through dissection and 3D reconstruction of the internal anatomy. Of particular interest is the hypertrophied circulatory system. A well-developed ctenidium supported by extensive blood sinuses provides oxygen for the host but the circulatory system is enlarged beyond the scope of other similar vent gastropods. It has a remarkably voluminous heart representing approximately 4% of the body volume, with a very muscular ventricle. This proportionally giant heart primarily supplies the highly vascularised oesophageal gland, the organ that houses the endosymbionts. Thus we infer the elaborate cardiovascular system most likely evolved to oxygenate the endosymbionts in a hypoxic environment and/or to supply them with hydrogen sulfide. As a result of specialisation to resolve energetic needs in a chemosynthetic environment, this dramatic ‘dragon-like’ species has become a carrying vessel for its bacteria.
