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Next article FreeAbout the CoverPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreCoverThe images on the cover depict two morphotypes of the scaly-foot gastropod Chrysomallon squamiferum from deep-sea hydrothermal vents in the Indian Ocean, over 2300 meters in depth. This is the only gastropod mollusc known to exhibit dermal scales. The color is linked to vent fluid chemistry: a higher iron sulfide content leads to a darker coloration.The extraordinary feature of the scaly-foot, however, is hidden underneath its scale armor, in its anatomy. This snail has a specialized internal organ to house chemoautotrophic symbionts, as well as an unusually hypertrophied circulatory system to supply nutrients to these endosymbionts. This strategy is distinct from other vent holobiont molluscs, which host bacteria in the gill epidermis that comes in direct contact with vent fluid and which have less extensive circulatory systems, exemplified by the provannid Alviniconcha marisindica that co-occurs with the scaly-foot.On pages 102–112 of this issue, J. D. Sigwart and C. Chen report on the physiology of Indian Ocean vent animals, using closed-chamber respirometry to investigate whether the scaly-foot’s strategy of having an internal symbiont-housing organ increases its routine metabolism. By comparing the oxygen consumption of both Chrysomallon and Alviniconcha at different temperatures, they show that housing symbionts in an internal organ does not fundamentally increase the oxygen requirement. The scaly-foot, however, was able to maintain a steady metabolic demand across experiment temperatures, while Alviniconcha showed stress responses at low temperature. Vent habitats have steep temperature gradients between the superheated vent fluid and the cold surrounding seawater, and such physiological constraints likely play important roles in defining niches in these environments.Credits: Top photo (white), Suguru Nemoto, Enoshima Aquarium; bottom photo (dark), David Shale. Cover design, Jeannie Harrell, University of Chicago Press. Next article DetailsFiguresReferencesCited by The Biological Bulletin Volume 235, Number 2October 2018 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.1086/701310 © 2018 by The University of Chicago. All rights reserved.PDF download Crossref reports no articles citing this article.