**Author details**

series of investigations aimed at characterizing molecular indicators of adaptation processes of which components of the immune and antioxidative stress response systems have received most of our attention. As a research goal, long‐term maintenance of vent mussels to atmo‐ spheric pressure was instrumental to further our understanding on molecular relationships under which the vent mussel‐endosymbiont interactions are affected by aquaria conditions and by the gradual disappearance of endosymbiont bacteria from gill epithelia. Hence, the maintenance of live mussels in our aquarium laboratory system has been a key factor in gain‐ ing knowledge into the physiology of vent animals including the study of evolutionary con‐ served immune, inflammatory, and stress‐related factors commonly found in other marine bivalves. *In vivo* and *ex vivo* experiments conducted with live mussels and their excised gill tissues as primary tissue cultures, allowed the specific host‐endosymbiont interactions to be revealed, and further characterized in the deep‐sea vent model *B. azoricus*, establishing dis‐ tinct genetic signatures for the expression of endosymbiont genes and host‐immune genes in relation to different environmental conditions. Increasing evidence now support the role of gills as a *bone fide* immune‐responsive tissue in *B. azoricus*, consistent with a suitable study model for exploring molecular interactions involving host‐endosymbiont‐mediated immune recognition events and adaptation mechanisms to deep‐sea hydrothermal vent environments. Such adaptation mechanisms are likely to be influenced by the microbial community com‐ position surrounding the mussel beds at hydrothermal vents and therefore it is important to continue metatranscriptomic and metagenomic studies [79] from the gill‐associated microbial diversity and surrounding hydrothermal vent sediments [80, 81] in view of the broader eco‐ logical organization and evolutionary importance of animal‐bacterial microbiomes in chemo‐

In recent years, researchers have turned to the human microbiome for its functional role in human health [84] and both composition and alterations in the microbiome have been found associated with diabetes, inflammatory bowel disease, obesity, asthma, rheuma‐ toid arthritis, and susceptibility to infections [85]. Other microbiomes from nonmamma‐ lian and nonvertebrate species have also been characterized, for instance in insects where it was found to be highly dependent on the environment, species, and populations and affecting the fitness of species. These fitness effects may have important implications for the conservation and management of species and populations [82, 83]. Given the temporal instability of deep‐sea hydrothermal vents and their constant fluctuations of physical and chemical environmental conditions, vent animal‐microbiome associations have become critical for our understanding of invasion of nonnative species, responses to pathogens, and responses to chemicals and global climate change in the present and future [82] par‐ ticularly when deep‐sea mining activities are projected to have a major impact on deep‐sea

Acknowledgements are due to IMAR—Marine Institute, Research and Development Unit #531 in the Azores (Thematic Area E) and Portuguese Fundação para a Ciência e Tecnologia

synthetic‐based ecosystems in the deep sea [82, 83].

vent ecosystems [86].

178 Organismal and Molecular Malacology

**Acknowledgements**

Raul Bettencourt1,2,3\*, Inês Barros2,3, Eva Martins1,2, Inês Martins1,2,3, Teresa Cerqueira2,4, Ana Colaço1,2,3, Valentina Costa2,3,4, Domitília Rosa4 , Hugo Froufe5 , Conceição Egas5 , Sergio Stefanni6 , Paul Dando7 and Ricardo S. Santos1,2,3,4

\*Address all correspondence to: raul.s.bettencourt@uac.pt

1 IMAR, Marine Institute, Azores, Horta, Portugal

2 MARE, Marine and Environmental Sciences Centre, Azores, Horta, Portugal

3 OKEANOS, Research Unit, Faculty of Science and Technology, University of the Azores, Horta, Azores, Portugal

4 Department of Oceanography and Fisheries, Faculty of Science and Technology, University of the Azores, Horta, Portugal

5 Next Generation Sequencing Unit, UCBiotech, CNC, Parque Tecnológico de Cantanhede, Cantanhede, Portugal

6 Stazione Zoologica A Dohrn, Napoli, Italy

7 Marine Biological Association of the UK, Plymouth, United Kingdom
