Journal of the Marine Biological Association of the United Kingdom

Research Article

A new species of Exrima, synonymy of four species of Aphotopontius, Stygiopontius and Rhogobius, and record of first copepodid stage of Dirivultidae (Copepoda: Siphonostomatoida) from deep-sea hydrothermal vents of the East Pacific Rise (13°N)

Viatcheslav N. Ivanenkoa1 c1, Danielle Defayea2, Michel Segonzaca2, Alexis Khripounoffa3, Jozée Sarrazina3 and Frank D. Ferraria4

a1 Department of Invertebrate Zoology, Biological Faculty, Moscow State University, Moscow 119899, Russia

a2 Muséum National d'Histoire Naturelle, Département Milieux et Peuplements Aquatiques, UMR 7208, 61, rue de Buffon, 75005 Paris, France

a3 Institut Français de Recherche pour l'Exploitation de la MER, Département Etude des Ecosystèmes Profonds, Laboratoire Environnement Profond, Centre de Brest-BP 70, 29280 Plouzané, France

a4 IZ/MSC; MRC-534, National Museum of Natural History, Smithsonian Institution, 4210 Silver Hill Road, Suitland, MD 20746 USA

Abstract

Females of the new species Exrima walteri sp. nov. were found in sediment trap samples deployed over different sites of the East Pacific Rise (13°N) at 2600 m depth. Four traps were deposited during the HOPE99 cruise (1999) and recovered during the AMISTAD (1999) cruise on the research vessel ‘L'Atalante’. The new species is distinguished from congeners, E. singula Humes, 1987 and E. dolichopus Humes, 1987, by the following derived characters: first somite of the urosome with 3 (one dorsal and two lateral) stout conical extensions; distal endopodal segment on the swimming leg 4 broad. In addition, many specimens of copepodids I and lecithotrophic nauplii, identified as belonging to Dirivultidae gen. sp., were found in the samples of all sediment traps. This is the first record of copepodids I and of a nauplius of dirivultids from the Pacific Ocean. Study of type and additional material collected during different Ifremer cruises at different vent sites (HERO91, EXOMAR, PHARE and MoMARETO) required synonymy of four species of Aphotopontius Humes, 1987, Stygiopontius Humes, 1987 and Rhogobius Humes, 1987. Aphotopontius rapunculus Humes and Segonzac, 1998 is transferred to the genus Rhogobius because it possesses all presumed derived attributes of this genus: last abdominal somite with lobes at sides of anal operculum; second segment of antennal endopod elongate and slender. A new study of the type material suggests that: Aphotopontius temperatus Humes, 1997 is a synonym of A. atlanteus Humes, 1996; Stygiopontius lumiger Humes, 1989 is a synonym of S. sentifer Humes, 1987 while S. bulbisetiger Humes, 1996 is a synonym of S. pectinatus Humes, 1987. Females of the three synonymized species were found to be sub-adult females at copepodid V. Leg 6 on these specimens is one seta located dorsolaterally on the posterior part of the genital somite. This position for leg 6 is unknown for copepodid V of other siphonostomatoids whose leg 6 is located ventrally at copepodid V; the dorsolateral position is presumed derived and shared by the dirivultid genera Aphotopontius Humes, 1987 and Stygiopontius Humes, 1987. A new key to the Dirivultidae genera is presented.

(Received July 31 2010)

(Accepted January 11 2011)

(Online publication March 14 2011)

Correspondence:

c1 Correspondence should be addressed to: V.N. Ivanenko, Department of Invertebrate Zoology, Biological Faculty, Moscow State University, Moscow 119899, Russia emails: ivanenko@mail.bio.msu.ru, ivanenko.slava@gmail.com