Two new melanodrymiid snails from the East Pacific Rise indicate the potential role of inactive vents as evolutionary stepping-stones

Abstract

Since their discovery in 1977, animals specialized to life in active deep-sea hydrothermal vents have been the focus of many studies. Inactive spires in the vent periphery, however, have received little attention. Recent shifts of deep-sea mining interests from active vents to inactive sulphide deposits have led to an urgent need to characterize the inactive vent fauna. Here, we report two new species of the vent-endemic genus Melanodrymia that are apparently specific to surfaces of inactive sulphides on the East Pacific Rise. Melanodrymia laurelin sp. nov. and M. telperion sp. nov. are easily distinguished from other congeners by shell shape and sculpture; their standings as distinct species are supported by molecular analyses using the mitochondrial cytochrome c oxidase subunit I (COI) gene. They were collected together with numerous specimens of M. galeronae, another species originally described some distance away from active vents. Phylogenetic reconstruction indicates Melanodrymia species living in active vents likely evolved from ancestors specializing in inactive spires, and in turn from sunken wood. Our findings add to the growing evidence that inactive sulphides host unique species, bolstering the need to better understand these systems before any anthropogenic exploitation takes place.

https://zoobank.org/urn:lsid:zoobank.org:pub:D8E8EB3F-B246-4962-B70C-1CD94AEB134D

Key words:

• Deep sea
• hydrothermal vent
• Melanodrymiidae
• Neomphalida
• Neomphalina
• Neomphaliones
• polymetallic sulphides

Acknowledgements

We thank the captain and crew of R/V Atlantis cruise AT50-06 for their support of the scientific activities; and we extend our thanks to the HOV Alvin team. We are grateful to the scientific party on-board cruise AT50-06, led by chief scientist Shawn Arellano (Western Washington University), for collecting the specimens of Melanodrymia studied herein. We gratefully acknowledge Michael Meneses (Woods Hole Oceanographic Institution) for directing sampling at sea and sorting the gastropod specimens, and Susan Mills (Woods Hole Oceanographic Institution) for directing our attention to the protoconch morphology. Distribution data from this manuscript will be deposited in BCO-DMO (Biological & Chemical Oceanography Data Management Office) and provided to OBIS (Ocean Biodiversity Information System. Comments and edits from José H. Leal (Bailey-Matthews National Shell Museum) and another anonymous reviewer improved an earlier version of this paper. Inspirations for the new species names came from J. R. R. Tolkien’s legendarium, as well as the Lord of the Rings (2001–2003) and The Hobbit (2012–2014) film trilogies directed by Peter Jackson.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Associate Editor: Barna Pall-Gergely

Additional information

Funding

Collection of the Melanodrymia specimens used herein was funded by the U.S. National Science Foundation grants OCE 1947735 (to Lauren S. Mullineaux) and OCE 2152453 (to Lauren S. Mullineaux and Stace E. Beaulieu).