Two deep-living rhodaliids (Cnidaria, Siphonophora) from the Mid-Atlantic Ridge

Type Article
Date 2017
Language English
Author(s) Mapstone Gillian M.1, Corbari Laure2, Menot LenaickORCID3
Affiliation(s) 1 : Nat Hist Museum, Dept Life Sci, Cromwell Rd, London SW7 5BD, England.
2 : Museum Natl Hist Nat, Inst Systemat Evolut & Biodiversite, UMR 7205, Paris, France.
3 : Ctr Bretagne, IFREMER, REM EEP, Lab Environm Profond, Plouzane, France.
Source Marine Biology Research (1745-1000) (Taylor & Francis As), 2017 , Vol. 13 , N. 5 , P. 486-493
DOI 10.1080/17451000.2016.1232830
WOS© Times Cited 2
Note Thematic Issue No. 10: Thirty Years of the Hydrozoan Society: New Challenges in Hydrozoan Studies, guest edited by Stefania Puce
Keyword(s) Deep-sea, Mid-Atlantic Ridge, rhodaliid, siphonophore
Abstract Rhodaliids are a semi-benthic family of 14 physonect siphonophore species found in all oceans, except the Mediterranean and Arctic. They inhabit species-specific depth ranges in isolated locations and records are mostly sparse. Here, the first ever observations of rhodaliids from the Mid-Atlantic Ridge are given, from three images of two putative species. They come from depths of 3482 and 3667–3670 metres, on the Mid-Atlantic Ridge (MAR) at 23°N and 26°N, near two hydrothermal vents. Rhodaliids are very delicate animals and extremely hard to sample, particularly from such great depths, and the only comparable deep-living species so far described is the Galapagos Dandelion (Thermopalia taraxaca) from 2480–2938 metres on the Galapagos Rift and East Pacific Rise. This species inhabits the outer zone of certain hydrothermal vents where there is no hydrogen sulphide in the water, but connectivity with the MAR species is unlikely, since the latter inhabit a different ocean basin. Two, or possibly three, rhodaliid species have so far been collected in the North Atlantic, and all occurred near continental margins. These new observations are therefore important, and the images included here will hopefully alert future expeditions to hunt for, and perhaps even collect, more specimens. Rhodaliids are mostly observed individually adhering to a variety of substrata with their long tentacles, but very occasionally abundances of from 1 to 11 individuals m−2 have been noted. Rhodaliids feed on copepods, other small pelagic crustaceans and fish larvae, and can thus represent important members of deep-sea ecosystems. This paper provides a distribution map of all species with an accompanying table showing coordinates, depths and number of specimens collected, and a second table of comparative diagnostic rhodaliid characters, which is used to suggest possible identities for the two putative new MAR species.
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