New records on sea anemones (Anthozoa: Actiniaria) from hydrothermal vents and cold seeps

New records on sea anemones (Anthozoa: Actiniaria) from hydrothermal vents and cold seeps P.J. López-González, E. Rodríguez, J.-M. Gili & M. Segonzac López-González, P.J., E. Rodríguez, J.-M. Gili & M. Segonzac. New records on sea anemones (Anthozoa: Actiniaria) from hydrothermal vents and cold seeps. Zool. Verh. Leiden 345, 31.x.2003: 215-243, figs 1-16.— ISSN 0024-1652/ISBN 90-73239-89-3. Pablo J. López-González, Departamento de Fisiología y Zoología, Facultad de Biología, Universidad de Sevilla, Reina Mercedes 6, 41012 - Sevilla, Spain (e-mail: [email protected]). Estefanía Rodríguez, Departamento de Fisiología y Zoología, Facultad de Biología, Universidad de Sevilla, Reina Mercedes 6, 41012 – Sevilla, Spain / Departamento de Biología Marina y Oceanografía, Instituto de Ciencias del Mar, CMIMA (CSIC), Paseo Marítimo de la Barceloneta, 37-49, 08003 Barcelona, Spain (e-mail: [email protected]). Josep-Maria Gili, Departamento de Biología Marina y Oceanografía, Instituto de Ciencias del Mar, CMIMA (CSIC), Paseo Marítimo de la Barceloneta, 37-49, 08003 Barcelona, Spain (e-mail: gili@cmima. csic.es). Michel Segonzac, Ifremer, Centre de Brest, DRO-EP/Centob, BP 70, 29280 Plouzané, France (e-mail: [email protected]). Key words: Cnidaria; Anthozoa; Actinostolidae; Paranthosactis denhartogi gen. et spec. nov.; Hadalanthus aff. knudseni; Maractis rimicarivora; hydrothermal vents; cold seeps. During several cruises carried out by the Ifremer (Institut français de recherche pour l’exploitation de la mer) with the submersile “Nautile” at different hydrothermal sites and cold seeps, an important collection of anthozoans - mainly actiniarians - was sampled. Additional material was collected by an American cruise with the submersile “Alvin”. The goal of the present contribution is to describe part of this actiniarian fauna inhabiting three chemoautotrophic sites, one of them in the Mid-Atlantic Rise and the other two in the Eastern Pacific. A new genus and species of actinostolids is proposed after the study of specimens collected at hydrothermal vents in the Guaymas Basin (East Pacific Rise, Gulf of California, 27º00’N-111º24’W, 2020 m). Furthermore, some specimens collected in cold seeps along the MAT (Middle America Trench, off Mexico, 18º21’-20°01’N 104º21’-106º17’W, 3354-3795 m) are reported as Hadalanthus aff. knudseni. This material is discussed and compared with the existing type material of H. knudseni Carlgren, 1956, and Tealidium jungerseni Carlgren, 1921. In addition, some specimens of Maractis rimicarivora Fautin & Barber, 1999, were collected at hydrothermal vents of the Mid Atlantic Ridge Snake Pit (23º22.9’N-44º55.8’W, 3490 m) site. This species is collected for the first time after its original description at Trans-Atlantic Geotraverse (TAG, 26º08’N 44º49.6’W, 3650 m). Some ecological remarks are given from in situ and video observations. Introduction Hydrothermal vents and cold seeps are characterized by low diversity - but highbiomass - communities. Tube worms (polychaetes and vestimentifera), large bivalves, gastropods, different types of crustaceans (copepods, amphipods, shrimps, brachyurans), and fishes are representative faunistic elements of hydrothermal vent and cold seep sites. Little is known about hydrothermal and cold seep sea anemones (see review by Van Dover, 2000 for vents and Sibuet & Olu, 1998 for seeps), although they have sometimes been observed to be abundant enough to play an important role in the deep sea environments and in the hydrothermal vent food web (see Doumenc & Van Praët, 1988; Gage & Tyler, 1991; Van Dover, 2000, for additional references). They López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003)216 were often reported at seeps, attached on bivalve shells or on other substrates (e.g. Juniper & Sibuet, 1987; Barry et al., 1996; Olu et al., 1997). In spite of the presence of locally dense beds, an endoor episymbiotic relationship with chemoautotrophic bacteria has not been empirically determined. Sea anemones are presumed to be suspension feeders capturing a wide range of prey including large prey items (e.g. Shick, 1991; Van Dover et al., 1997; Fautin & Barber, 1999; Van Dover, 2000). Nothing is known about speciation, evolution or biogeographic processes in sea anemones inhabiting these chemoautotrophic environments. A high level of endemism is expected and may corroborate the idea of reduced gene flow between locations. The evaluation of the potentially restricted gene flow is particularly important with respect to speciation. The Indo-Pacific shows a complex tectonic history in comparison with the Mid-Atlantic Ridge, including four of the six biogeographic provinces (Van Dover, 2000; Van Dover et al., 2001, 2002). In this scenario, most of the sea anemone species reported from hydrothermal vents are currently known from Indo-Pacific sites, while only two species are known inhabiting Atlantic hydrothermal vents. Seven species of sea anemones have been documented from hydrothermal vents. Five species are members of the family Actinostolidae and two species were Hormathiidae, they all belong to the two richest families of deep-sea actiniarians (Desbruyères & Segonzac, 1997; Fautin & Barber, 1999). The Atlantic actinostolids associated with hydrothermal vents only include two species, namely, Parasicyonis ingolfi Carlgren, 1942 and Maractis rimicarivora Fautin & Barber, 1999 (see Segonzac, 1992; Fautin & Barber, 1999). P. ingolfi was collected at Snake Pit (23º22.94’N-44º56.09’W, 3480 m), while M. rimicarivora was found at a northern location, Trans-Atlantic Geotraverse (TAG, 26º08’N 44º49.6’W, 3650 m). From the Pacific, three other actinostolid species have been reported (one of them identified only at generic level): Actinostola sp., Cyananthea hydrothermala Doumenc & Van-Praët, 1988, and Marianactis bythios Fautin & Hessler, 1989 (see Doumenc & Van-Praët, 1988, Fautin & Hessler, 1989). The Fig. 1. Locator map indicating the hydrothermal vents or cold seep where the species described in this paper are present. 217López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003) two former species were collected at 12º48’-49’N-103º56’ (2630-2635 m), while M. bythios was found at Mariana back-arc basin 18º10.9’-12.6’N 144º42.4’-43.2’E (3660 m). The hormathid species reported from hydrothermal vents, one of them only identified at generic level, were collected at 12º48’-49’N-103º56’ (2630-2635 m) in the Eastern Pacific Rise (EPR): Chondrophellia coronata (Verrill, 1883) and Phelliactis sp. (see Doumenc & Van-Praët, 1988). Three species of sea anemones have been reported from cold seep sites, the Hormathidae Monactis vestita (Gravier, 1918), from deep Barbados prism mud volcanoes, 4980 m (Olu et al., 1997) and two Actinostolidae from the Monterey Bay seeps, both only identified at generic level, Stomphia sp. and Paractinostola sp., 1000 m (Barry et al., 1996). In this paper, we describe a new genus and species of actinostolid from hydrothermal vents at Guaymas Basin collected during the GUAYNAUT cruise (Eastern Pacific, Nov-Dec 1991). Furthermore, we describe as Hadalanthus aff. knudseni some specimens attributable to the monotypic genus Hadalanthus Carlgren, 1956, collected from cold seeps at Middle America Trench off Mexico (18°-19°N; Mercier de Lépinay, 1997) during the NAUTIMATE cruise (Eastern Pacific Rise, Jan-Feb 1994). Finally, we give descriptions of the four specimens of Maractis rimicarivora collected from the hydrothermal vents at Snake Pit during the recent American cruise DIVERSExpedition (MidAtlantic Ridge, Jul 2001). Material and Methods This paper is based in part on the material collected in three chemoautotrophic environments, two of them were hydrothermal sites [Guaymas Basin, 2020 m (Eastern Pacific Rise, EPR) and Snake Pit, 3500 m (Mid-Atlantic Ridge, MAR)] and the last one a cold seep system, 3354-3795 m (Middle American Trench) (fig. 1). The GUAYNAUT cruise was supported by the Ifremer, Brest, and the Universidad Autónoma de México (UNAM), and was conducted by A-M. Alayse, (Ifremer, Centre de Brest), on board the R/V “Nadir” and the R/V “El Puma”, the former equipped with the submersible “Nautile”, from 8 November to 7 December 1991. The main goal of this cruise was the study of the ecology of the Guaymas Basin hydrothermal vent system, mainly from the point of view of its bacterian communities and the chemistry of the fluids and the sediments (Marchand et al., 1994; Guézennec et al., 1996), but also the distribution of the megaand meiofauna. The NAUTIMATE cruise was supported by the Université UPMC, Paris, Ifremer, UNAM (México) and Texas A&M University, and was conducted by B. Mercier de Lépinay (Université de Nice-Sophia-Antipolis) and F. Michaud (Laboratoire de Géodynamique sous-marine, Villefranche-sur-mer), on board the R/V “Nadir” equipped with the submersible “Nautile”, from 16 January to 9 February 1994. The main goal of this cruise was the study of some geodynamic aspects of the neogene subsidence along the Middle America Trench off Mexico (18°-19°N). In addition some biological observations and samples were collected from this cold seep. The American cruise DIVERSExpedition was conducted by C. Van Dover (College of William & Mary, Williamsburg, USA), with the participation of American, Portuguese and French institutions (e.g. College of William & Mary, WHOI, Universidade dos Açores and Ifremer), on board the R/V “Atlantis” equipped with the sub- López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003)218 AB CD EF 219López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003) mersible “Alvin”, from 26 June to 29 July 2001. The main goal of this cruise was to prospect and compare the invertebrate composition and biomass associated with beds of the bivalves Bathymodiolus spp. at different hydrothermal sites in MAR (Logatchev, Snake Pit, Lucky Strike, Broken Spur). The sea anemones collected in the before mentioned cruises were fixed in 10% seawater formalin, and then preserved in 70% ethanol. Fragments from selected specimens were dehydrated in buthanol (Johansen, 1940), and embedded in paraffin. Histological sections 7-8 µm thick were stained with Ramón y Cajal’s Triple Stain (Gabe, 1968). Cnidae measurements were taken from preserved material in squash preparations at 1000x magnification with Nomarski differential interference contrast optics. Frequencies given are subjective impressions based on squash preparations. For purposes of comparison, the following type material was examined: - Tealidium jungerseni Carlgren, 1921. 1 syntype (SMNH-type-5568), Ingolf-Expedition, stn 11, Danmark Strait, 64º34’N-31º12’W, 1300 fms, 21 May 1895; 2 specimens (ZMUC), Ingolf Expedition, stn 11, Danmark Strait, 64º34’N-31º12’W, 1300 fms, 21 May 1895; 1 specimen (ZMUC), Ingolf Expedition, stn 38, Davis Strait, 59º12’N51º05’W, 1870 fms, 30 Jul 1895. - Hadalanthus knudseni Carlgren, 1956. 2 paratypes (ZMUC), Galathea Expedition, stn 658, 35º51’S-178º31’W, SW Pacific, 6660-6720 m. Remarks: From these fragmented specimens only a few cnidae measurements were obtained. Tenaculi are present as described in the original description by Carlgren (1956). The material studied in this article is deposited in the Muséum national d’Histoire naturelle in Paris (MNHN), the Zoological Museum in Copenhagen (ZMUC), the Swedish Museum of Natural History in Stockholm (SMNH), and in the Zoology Section of the Faculty of Biology at the University of Seville in Spain (SZ). Results Family Actinostolidae Carlgren, 1932 Paranthosactis gen. nov. Diagnosis.— Actinostolidae with well developed pedal disc. Column smooth (domeshaped to cylindrical in preserved material), not divisible into scapus and scapulus. Fig. 2. Photographs taken in situ at the different chemoautotrophic environments prospected. A) specimens of Paranthosactis denhartogi gen. nov. spec. nov. with the vestimentiferan Riftia pachyptila (one living specimen and two dead ones) on active hydrothermal edifice at the Guaymas Basin at 2020 m depth. Copyright: “Photograph Ifremer/Guaynaut-1991”; B) detail of Paranthosactis denhartogi gen. nov. spec. nov. close to some living specimens of Riftia pachyptila. Copyright: “Photograph Ifremer/Guaynaut-1991”; C) specimens of Hadalanthus aff. knudseni Carlgren, 1956 (brownish tentacles) on dead and living bivalve shells of Calyptogena sp., and the galatheid crab Munidopsis subsquamosa at cold seeps, 3795 m depth, in the Middle American Trench. Copyright: “Photograph Ifremer/Nautimate-1994”; D) oral view of some specimens of H. aff. knudseni living next to cold seeps. Copyright: “Photograph Ifremer/Nautimate-1994”; E) general view of Snake Pit-Elan hydrothermal site at Mid-Atlantic Ridge, 3500 m depth, showing some actiniarians, the mytilid Bathymodiolus putoserpentis, the ophiurid Ophioctenella acies and the fish Pachycara thermophilum. Copyright: “WHOI/DIVERSExpedition-2001”; F) Detail of the sea anemone Maractis rimicarivora Fautin & Barber, 1999 at Snake Pit-Elan, 3500 m. Copyright: “WHOI/DIVERSExpedition-2001”.  López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003)220 Sphincter distinctly marked on the surface of the column as a prominent circumferential marginal ring; moderately strong, mesogloeal. Tentacles of uniform thickness along entire length (not completely hidden in preserved retracted material). Inner tentacles longer than outer; not numerous (about 70). Longitudinal tentacle and oral disc circular musculature ectodermal; that of tentacles equally well developed on all sides. Mesenteries not arrayed according to Actinostola rule; first cycle of mesenteries perfect; all stronger ones fertile, including the directives. Two well developed siphonoglyphs and two pairs of directives. Retractor muscles diffuse; parietobasilar muscles not differentiated; basilar musculature differentiated. Mesogloea relatively thin. Same number of mesenteries distally and proximally. Cnidom: spirocysts, basitrichs, microbasic b-mastigophors(?), microbasic p-mastigophors. Type species.— Paranthosactis denhartogi spec. nov. Etymology and gender.— The generic name refers to the morphological similitude of the new taxon to the genus Anthosactis Danielssen, 1890. The gender is feminine. Fig. 3. Paranthosactis denhartogi gen. et spec. nov. Preserved specimens. A) holotype, MNHN; B) SZ (ANT-2138); C) SZ (ANT-2138); D) MNHN, detail of the distal part of the column and tentacles. Abbreviations: co, column; mr, marginal ring; te, tentacles. Scale bars: A-C, 10 mm; D, 4 mm. AB CD 221López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003) Paranthosactis denhartogi spec. nov. (figs 2A-B, 3-7, table 1) Material.— MNHN, holotype, one specimen, GUAYNAUT cruise, Gulf of California, Guaymas Basin, PL 16, 27º00.94’N-111º24.66’W, 2025 m depth, 28.xi.1991; MNHN, paratypes, 2 specimens, with the same sampling data as the holotype; MNHN, 2 specimens, GUAYNAUT cruise, Gulf of California, Guaymas Basin, PL 07, 27º00.45’N-111º24.53’W, 2020 m depth, 16.xi.1991; SZ (ANT-2137), 2 specimens, GUAYNAUT cruise, Gulf of California, Guaymas Basin, PL 07, 27º00.45’N-111º24.53’W, 2020 m depth, 16.xi.1991; SZ (ANT-2138), 2 specimens, GUAYNAUT cruise, Gulf of California, Guaymas Basin, PL 16, 27º00.94’N-111º24.66’W, 2025 m depth, 28.xi.1991. Description.— External anatomy (fig. 3): Column smooth, much broader proximally than distally; to 16 mm diameter and 15 mm height in preserved and partially retracted specimens. Pedal disc well developed and enlarged, to 35 mm at maximum axis; some specimens with foreign sulphide particles adhered to it. Column smooth, with a marginal prominent ring corresponding to the muscular sphincter (fig. 3B, D). Oral disc not observed in preserved material. Tentacles about 70 in number, outer tentacles shorter than inner ones, up to 8 mm and not completely withdrawn in preTable 1. Size ranges of the cnidae of Paranthosactis denhartogi gen. et spec. nov. X: average. SD: standard deviation. Samples: the ratio indicates the number of polyps in which each cnidae was found out and the number of polyps of each species examined. N: indicates the total number of capsules measured. F: Frequency: +++ = very common, ++ = common, + = rather common, --- = sporadic. Abbreviation: Mc, Microbasic. Categories Range of length and X±SD Sample N F width of capsules in µm Pedal disc Basitrichs (B,C) (17.2-20.2) 3.0 18.6± 1.2 3.0±0.0* 1/1 17 +/++ Column Basitrichs (B,C) (15.1-21.2) (3.0-4.0) 18.3±1.4 3.6±0.5 4/4 67 ++ Tentacles apex Spirocysts (A) (17.2-56.6) (3.0-9.1) 31.2±8.0 5.0±0.2 6/6 80 +++ Basitrichs (B,C) (19.2-30.3) (2.0-4.0) 25.4±2.9 3.2±0.4 6/6 77 ++/+++ Mc. b-mastigophores(?) 1 (D) (24.2-27.3) 4.0 25.6±1.5 4.0±0.0* 2/6 3 --- Mc. p-mastigophores 1 (F) (16.2-19.2) (4.0-5.0) 18.2±1.1 4.5±0.5* 5/6 7 --- Tentacles base Spirocysts (A) (11.1-50.5) (4.0-9.1) 27.3±7.5 5.3±1.3 6/6 80 ++/+++ Basitrichs (B,C) (17.2-25.2) (2.0-4.0) 21.1±1.65 3.0±0.3 6/6 47 ++/+++ Actinopharynx Basitrichs (B,C) (15.1-33.3) (2.0-4.0) 26.8±3.8 3.1±0.4 4/4 46 +/++ Mc. p-mastigophores 2 (G) (30.3-43.4) (4.0-6.1) 34.7±2.3 4.6±0.5 4/4 80 ++/+++ Mc. p-mastigophores 3 (H) (31.3-42.4) (4.0-6.1) 38.2±3.4 5.2±0.6* 3/4 21 + Mc. b-mastigophores(?) 2 (E) (39.4-45.4) (4.0-5.0) 42.4±3.03 4.7±0.6* 1/4 3 --- Filaments Basitrichs (B,C) (12.1-21.2) (2.0-4.0) 15.5±2.0 2.8±0.5* 4/4 31 ---/+ Mc. p-mastigophores 2 (G) (24.2-40.4) (4.0-6.1) 34.7±2.7 4.7±0.6 4/4 70 ++/+++ Mc. p-mastigophores 3 (H) 37.4 (5.0-6.1) 37.4±0.0 5.6±0.7* 1/4 2 + * Average based on less than 40 measured capsules. The measurement of at least 40 capsules is usually considered enough to have significance. López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003)222 Fig. 4. Paranthosactis denhartogi gen. et spec. nov. (SZ (ANT-2138)) A) cross section at stomodaeum level; B) directives; C) basilar musculature. Abbreviations: 1, pair of mesenteries of the first cycle; 2, pair of mesenteries of the second cycle; 3, pair of mesenteries of the third cycle; bm, basilar muscle; di, directives; ms, mesentery; pd, pedal disc; ph, pharynx; rm, retractor muscle. Scale bars: A, 0.6 mm; B, 0.45 mm; C, 0.1 mm. A BC 223López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003) served specimens. Not thickened at base, with longitudinal and transverse furrows due to contraction. Internal anatomy (figs 4, 5, 6): Equal number of mesenteries distally and proximally. Mesenteries hexamerously arranged in four cycles, only the first cycle perfect. Three oldest cycles fertile, including directives. Fourth cycle incomplete, poorly developed and sterile. Two pairs of directives, connected with well-developed siphonoglyphs, mesogloea and gastrodermis of the siphonoglyphs slightly wider than the mesogloea and the gastrodermis of the actinopharynx. Retractor musculature diffuse at stomodaeum level (fig. 4A-B). Parietobasilar musculature not developed. Basilar musculature distinct but poorly developed (fig. 4C). Gametogenic tissue well developed in specimens collected in November; gonochoric; developing oocytes (to 0.13 mm in diameter on histological sections). Sphincter muscle mesogloeal, moderately strong, and relatively short (fig. 5). Oral disc and tentacles with ectodermal longitudinal musculature (fig. 6). Musculature of tentacles with similar development aboral and oral. Column wall of similar thickness entire length. Epidermis 0.02-0.08 mm thick; mesogloea 0.05-0.08 mm thick, and gastrodermis 0.10-0.15 mm thick. Cnidom: Spirocysts, basitrichs, microbasic b-mastigophores(?), and microbasic pmastigophores. No batteries of microbasic b-mastigophores (or supposed microbasic Fig. 5. Paranthosactis denhartogi gen. et spec. nov. (SZ (ANT-2138)) A) longitudinal section at margin showing mesogloeal sphincter, details showed in the figures B, C, and D are indicated; B-D) details from A. Abbreviation: sph, sphincter. Scale bars: A, 0.5 mm; B-D, 0.06 mm. AB C D López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003)230 animals show a brownish crown of tentacles, while the column is dirty white. Distribution and habitat.— At present, Hadalanthus aff. knudseni is known from the Eastern Pacific in the Middle American Trench off Manzanillo (Mexico), between 3354 and 3795 m. This area is the seat of cold seeps coming from the tectonic plate Rivera subduction, on the level of a fault system whose principal one is prolonged to the north into the basin of Guaymas. Colonies of bivalves vesicomyid Calyptogena sp. live on the sediment, often covered by a bacterial mat, at the exit of cold fluids charged of reduced compounds (CH4and SH2). The sea anemones are fixed on these bivalves (fig. 2C-D), alive, or more frequently on the shells, which constitutes the only hard substrate of these sedimentary areas. The accompanying fauna of these communities is very little diversified. It consists of a rare galathea crab Munidopsis subsquamosa (fide E. Macpherson), of zoarcid fish, and serpulid polychaetes Neovermilia sp. (fide H. Zibrowius). Taxonomic remarks.— According to Carlgren’s diagnosis (1956) and Fautin & Hessler’s key (1989), the present material can be included in the deep-sea genus Hadalanthus Carlgren, 1956 by the following set of features: 1) fertility of all stronger mesenteries, 2) ectodermal nature of longitudinal tentacles muscles, 3) six pairs of perfect mesenteries, 4) absence of microbasic b-mastigophores in tentacles, 5) presence of microbasic p-mastigophores in tentacles, 6) presence of a column divided into scapus Table 3. Size ranges of the cnidae of Hadalanthus aff. knudseni Carlgren, 1956. X: average. SD: standard deviation. Samples: the ratio indicates the number of polyps in which each cnidae was found out and the number of polyps of each species examined. N: indicates the total number of capsules measured. F: Frequency: +++ = very common, ++ = common, + = rather common, --- = sporadic. Abbreviation: Mc, Microbasic. Categories Range of length and X±SD Sample N F width of capsules in µm Pedal disc Basitrichs (C) (20.2-25.2) (2.0-3.0) 23.1±1.4 2.8±0.4* 2/2 26 ---/++ Scapus Basitrichs (C) (18.2-24.2) (2.0-3.0) 21.2±1.3 2.5±0.5 3/3 60 +++ Mc. p-mastigophores (D) (20.2-29.3) (3.0-6.1) 26.1±1.6 4.6±0.7 3/3 55 ++ Scapulus Basitrichs (C) (21.2-27.3) (3.0-4.0) 23.7±1.2 3.2±0.4 3/3 60 ++/+++ Mc. p-mastigophores (D) (24.2-35.3) (4.0-6.1) 28.3±2.0 5.1±0.7 3/3 60 +++ Tentacles Spirocysts (A) (18.2-50.5) (5.0-11.1) 30.1±7.2 7.2±1.6 5/5 75 ++/+++ Spirocysts (B) (18.2-36.4) (4.0-10.1) 26.3±4.4 5.1±1.2* 3/5 33 +/++ Basitrichs (C) (14.1-35.3) (2.0-4.0) 21.9±4.6 2.8±0.5 5/5 100 ++ Mc. p-mastigophores (D) (20.2-34.3) (4.0-7.1) 24.9±4.9 5.0±0.9 5/5 85 +/++ Holotrichs ? (E) (23.2-33.3) (6.1-8.1) 29.9±3.3 6.8±0.7* 4/5 8 --- Actinopharynx Basitrichs (B,C) (14.1-26.3) (2.0-4.0) 20.3±3.8 2.7±0.5 3/3 44 ++ Mc. p-mastigophores (D) (22.2-38.4) (4.0-7.1) 31.5±3.8 5.3±0.9 3/3 43 ++/+++ Filaments Basitrichs (B,C) (16.2-25.2) (2.0-3.0) 18.9±2.2 2.8±0.4 3/3 43 +/++ Mc. p-mastigophores (D) (23.2-36.4) (4.0-6.1) 30.1±3.5 4.8±0.5 3/3 48 +/++ * Average based on less than 40 measured capsules. The measurement of at least 40 capsules is usually considered enough to have significance. 231López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003) and scapulus, and 7) presence of distinct tenaculi on low mesogloeal papillae. Carlgren (1956: 13) pointed out the similar appearance of the column of Hadalanthus and Daontesia Carlgren, 1942, taking into account the absence of acontiae in the former genus. Among the actinostolid genera, the presence of mesogloeal papillae (eroded tenaculi ?) in the genus Tealidium could be considered a common feature with Hadalanthus (see Hertwig, 1882, Carlgren, 1921, 1949). However, sensu Carlgren (1949: 77) and Fautin & Hessler (1989: 817), the absence of batteries of nematocysts in tentacles is a distinctive character between both genera. In the examined type material of Tealidium jungerseni, there is no trace of cuticle or tenaculi, although the mesogloeal papillae are clearly visible on the column. However, in the examined type material of Hadalanthus knudseni, the tenaculi - visible at low magnification - are formed by a yellowish cuticle on small mesogloeal papillae. Despite the examination of the type material of Hadalanthus knudseni, it is difficult to decide whether the material collected during the NAUTIMATE cruise should be described as a new species or included under the name of the single species named in the genus Hadalanthus. The current state of the type material of H. knudseni does not allow to obtain more information about the structure of the distal tenaculi (in fact most of them are eroded), additional measurements of undischarged cnidae in order to obtain a positive or negative significance based on statistic analyses (most of them are exploded as indicated in the table 4), and other anatomical structures commonly used to solve specific questions. Thus, although our NAUTIMATE specimens show darker tenaculi (yellowish in the type material), flattened tenaculi distally (can not be observed in the type material due to the poor state of conservation) and some slight differences in the cnidae (these can not be compared by the scarce data obtained form the tissues of the type material, see tables 3 and 4), we identify the NAUTIMATE Fig. 9. Hadalanthus aff. knudseni Carlgren, 1956. Tenaculi on scapus. Note the variability in shape, flattened distally (A) [MNHN, to rounded or pointed at mid-column level (B and C) [MNHN]. Scale bars: A, 3 mm; B, 4 mm; C, 3.5 mm. AB C López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003)232 Table 4. Size ranges of the cnidae of Hadalanthus knudseni Carlgren, 1956 (Syntypes ZMUC). X: average. SD: standard deviation. Samples: the ratio indicates the number of polyps in which each cnidae was found out and the number of polyps of each species examined. N: indicates the total number of capsules measured. F: Frequency, +++ = very common, ++ = common, + = rather common, —- = sporadic. Abbreviation: Mc, Microbasic Categories Range of length and X±SD Sample N F Data from Carlgren, 1956 width of capsules in µm Pedal disc Basitrichs (26.6-30.3)  3.0 29.0±1.9  3.0±0.0* 1/1 4 + no data Scapus (1) Basitrichs (19.2-30.3)  3.0 24.4±2.5  3.1±0.3 2/2 55 ++ (24-32)  (2.8-3.5 Tentacles Spirocysts (27.3-51.5)  (6.1-7.1) 40.0±0.5  5.6±0.8* 2/2 11 ++ 50  5.6 Basitrichs 1 (34.3-42.4)  3.0 38.9±3.0  3.0±0.0* 1/2 6 + (38-43)  (2.8-3.5) Basitrichs 2 not found (48-53.6)  5 Basithichs 3 (14.1-24.2)  (2.0-3.0) 19.0±2.3  3.0±0.3* 2/2 22 ++ no data Mc. p-mastigophores(2) (29.3-35.3)  (4.0-5.0) 33.1±2.6  4.8±0.4* 2/2 9 +/++ (39.0-50.8)  5 Actinopharynx Basitrichs (20.2-30.3)  (3.0-4.0) 24.6±2.8  3.1±0.3* 1/1 20 ++ no data Mc. p-mastigophores(3) (41.4-51.5)  (5.0-6) 45.3±3.7  5.2±0.4* 1/1 8 ++ no data Filaments Basitrichs (16.2-26.3)  (3.0-4.0) 21.0±2.4  3.1±0.2 2/2 83 ++ (19.7-24)  3 Mc. p-mastigophores(4) (35.3-50.5)  (4.0-5.0) 41.4±4.6  4.8±0.4* 2/2 15 +++ (23-48)  4.5 * Average based on less than 40 measured capsules. The measurement of at least 40 capsules is usually considered enough to have significance. (1) 4 exploded capsules (25.2-29.3)  5.0 have been also found. (2) 8 exploded capsules (30.3-40.4)  (4.0-5.0) have been also found. (3) numerous exploded capsules (42.4-50.5  4.0-5.0) have been also found; 5 exploded capsules (42.4-46.5)  (5.0-6.1) have been also found. (4) numerous exploded capsules (42.4-50.5  4.0-5.0) have been found; 52 exploded capsules (23.2)(31.3-48.5)  (4.0-6.1) have been also found. 233López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003) specimens as H. aff. knudseni because of the similitude in the other comparable characters. The available differentiating characters could be product of the large size of the NAUTIMATE specimens (e.g. about 140 tentacles in the larger individual, but about 70 in an individual of similar size as the type material of H. knudseni). Genus Maractis Fautin & Barber, 1999 Maractis rimicarivora Fautin & Barber, 1999 (figs 2E, F, 14-16, table 5) Maractis rimicarivora Fautin & Barber, 1999: 625, figs. 1-4. Material.— MNHN, 2 specimens, DIVERSExpedition cruise, Snake Pit-Elan (Mid-Atlantic Ridge), dive 3674, 23º22.90’N-44º55.80’W, 3490 m depth, 16.vii.2001; SZ (ANT-2141), 2 specimens, DIVERSExpedition cruise, Snake Pit-Elan (Mid-Atlantic Ridge), dive 3674, 23º22.90’N-44º55.80’W, 3490 m depth, 16.vii.2001. Fig. 10. Hadalanthus aff. knudseni Carlgren, 1956. (SZ (ANT-2139)). Cross section at stomodaeum level. Abbreviations: 1, pair of mesenteries of the first cycle; 2, pair of mesenteries of the second cycle; 3, pair of mesenteries of the third cycle; 4, pair of mesenteries of the fourth cycle; di, directives; si, siphonoglyph; Scale bar: 5 mm. López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003)234 Table 5. Size ranges of the cnidae of Maractis rimicarivora. X: average. SD: standard deviation. Samples: the ratio indicates the number of polyps in which each cnidae was found out and the number of polyps of each species examined. N: indicates the total number of capsules measured. F: Frequency: +++ = very common, ++ = common, + = rather common, —- = sporadic. Abbreviation: Mc, Microbasic. Present study Fautin & Barber (1999) Snake Pit, 3500 m TAG, 3650 m. Categories Range of length and X±SD Sample N F Range of length and Sample N width of capsules in µm width of capsules in µm Pedal disc Basitrichs (B) (22.2-30.3)  (3.0-4.0) 24.4±2.2  3.1±0.3 4/4 58 +/++ ----- Column Basitrichs (B) (19.2-29.3)  (3.0-4.0) 23.7±1.9  3.1±0.3 4/4 80 ++/+++ (19.5-31.5)  (1.9-3.9) 5/5 71 Mc. p-mastigophores 1 (D) (25.2-30.3)  (4.0-5.0) 27.4±1.9  4.3±0.5* 2/4 19 —-/++ (21.3-31.9)  (3.4-6.2) 4/5 54 Tentacles Spirocysts (A) (27.3-81.8)  (4.0-7.1) 47.9±12.9  5.1±1.0 4/4 80 +++ (30.0-78.5)  (2.8-7.3) 5/5 91 Basitrichs (B) (19.2-45.4)  (3.0-4.0) 35.4±5.2  3.5±0.5 4/4 67 ++ (31.0-48.4)  (2.5-3.8) 5/5 50 (17.2-25.5)  (1.6-2.9) 5/5 54 (19.2-43.4)  (1.9-3.8) 5/5 74 Holotrichs (G) (35.3-48.5)  (5.0-8.1) 42.4±3.9  6.0±0.7* 3/4 22 ---/+ (30.4-53.9)  (4.5-6.4) 5/5 39 Actinopharynx Basitrichs (B,C) (16.2-36.4)  (3.0-4.0) 23.8±6.9  3.1±0.2* 2/4 17 ---/+ (23.4-34.9)  (2.3-3.2) 3/4 9 Mc. p-mastigophores 1 (D, E) (29.3-41.4)  (3.0-5.0) 35.4±3.1  4.5±0.6 4/4 100 ++/+++ (28.6-42.1)  (4.1-5.2) 3/4 31 Mc. p-mastigophores 2 (F) (1) (30.3-39.4)  (4.0-6.1) 34.1±2.7  4.4±0.6* 2/4 15 + Filaments Basitrichs (C) (14.1-21.2)  (2.0-3.0) 17.3±1.7  2.9±0.3* 4/4 38 ---/++ (16.1-34.1)  (1.8-4.5) 5/5 61 Mc. p-mastigophores 1 (D, E) (28.3-39.4)  (4.0-5.0) 34.6±2.6  4.7±0.5 4/4 100 ++/+++ (26.9-38.9)  (3.3-5.7) 5/5 61 Mc. p-mastigophores 2 (F) (1) (30.3-37.4)  (4.0-6.1) 34.9±2.1  5.1±0.4* 2/4 15 ---/+ * Average based on less than 40 measured capsules. The measurement of at least 40 capsules is usually considered enough to have significance. (1) Although this category could be included with the precedent cnida by the overlapping size range, low frequency and low constancy in the sampled specimens, we have preferred to maintain it separated from the other microbasic p-mastigophore (D,E) by the short V-shaped end and relative length of the shaft. Examination of exploded capsules could give additional information about the structure of the spines rows and solve definitively if they should be considered as the same category or maintained them separated. 235López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003) Description.— External anatomy (fig. 14): Column with rough texture, much broader proximally than distally; to 28 mm diameter and 20 mm height in preserved specimens. Column with transversal furrows due to the contraction of the animals, some sulphide particles adhered to them. Pedal disc well developed and enlarged, to 41 mm along maximum axis, in some specimens with foreign sulphide particles adhered to it. Oral disc not observed in preserved material. Tentacles about 100, outer tentacles shorter than inner ones, up to 16 mm long, and not completely withdrawn in preserved specimens (fig. 14). No thickening at base, with longitudinal and transverse furrows due to the contraction. Internal anatomy (fig. 15): Equal number of mesenteries distally and proximally. Mesenteries hexamerously arranged in four cycles, only the first cycle perfect. All stronger mesenteries fertile. Two pairs of fertile directives, connected with strong and well-developed siphonoglyphs. Mesogloea and gastrodermis of the siphonoglyphs slightly wider than the mesogloea and the gastrodermis of the actinopharynx. Retractor musculature diffuse at stomodaeum level (fig. 15A). Parietobasilar musculature only clearly differentiable in the stronger cycles. Basilar musculature poorly developed. Fig. 11. Hadalanthus aff. knudseni Carlgren, 1956. (SZ (ANT-2139)). A) longitudinal section at margin showing mesogloeal sphincter; details showed in figures B and C are indicated; B) detail of mesogloeal sphincter; C) cross section of a tentacle, showing ectodermal musculature; D) tenaculi. A, 5 mm; B, 0.15 mm; C, 0.2 mm; D, 0.25 mm. AB C D López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003)236 Gametogenic tissue well developed in specimens collected in July; gonochoric; developing spermatic vesicles (to 0.25 mm in diameter in preserved specimens). Sphincter muscle mesogloeal, strong, relatively short, occupying all mesogloea with the muscle bundles reticulated (fig. 15B). Oral disc and tentacles with ectodermal longitudinal musculature (fig. 15C-D). Column wall of similar thickness along entire length. Epidermis 0.04-0.12 mm thick; mesogloea 0.06-0.19 mm thick, and gastrodermis 0.02-0.12 mm thick. Fig. 12. Hadalanthus aff. knudseni Carlgren, 1956. (SZ (ANT-2139)). A) tenaculi and its mesogloeal papilla, longitudinal section. Distal portion showed in B is indicated; B) detail of A. Abbreviations: ep, epidermis; me, mesogloea; mp, mesogloeal papilla; sc, stratified cuticle. Scale bars: A, 0.25 mm; B, 0.05 mm. Fig. 13. Hadalanthus aff. knudseni Carlgren, 1956. Cnidae. A) spirocyst A; B) spirocyst B; C) basitrich D) microbasic p-mastigophore E) holotrich(?). See text and table 3 for explanation. Scale bar: 20 µm A ABC DE B 237López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003) Cnidom: Spirocysts, basitrichs, holotrichs and microbasic p-mastigophores. A survey of the cnidae is presented in table 5 and figure 16. Colour: Preserved material of a yellowish to whitish colour. According to the photographs and video tapes taken in situ (fig. 2E-F) living animals are whitish in colour. Distribution and habitat.— At present Maractis rimicarivora is known to live in two hydrothermal sites at the Mid-Atlantic Ridge, TAG, 3650 m (Fautin & Barber, 1999), and Snake Pit-Elan, 3490 m (Segonzac, 1992, and present account). On these two sites, the sea anemones are fixed on sulphide rocks. They are increasingly dense as one approaches to the active area (until several tens of ind/m2), which makes the presence of this group a good indicator of presence of active sites. Some specimens are observed at the base of the black smokers where the temperature of fluids is ca 10°C. On the Elan site, accompanying fauna is composed by the tube-worm polychaetes Chaetopteridae, gastropods Phymorhynchus, shrimps Rimicaris exoculata and Chorocaris chacei, bivalves Bathymodiolus puteoserpentis and zoarcid fish Pachycara thermophilum. Shrimps R. exoculata can constitute prey for sea anemones living close to the black smokers (Van Dover et al., 1997), but not for the majority of the population that lives at distances the shrimps do not reach. Taxonomic remarks.— The material here described and collected at Snake Pit area agrees well in general aspects with the original description of Maractis rimicarivora (see Fautin & Barber, 1999). Only a relatively shorter, stronger and reticulate mesogloeal sphincter and the presence - in some specimens - of a sporadic nematocyst (fig. 16F) are the apparently differentiating features between TAG and Snake Pit material. Fautin & Barber (1999: 630) pointed out the presence of a small sea anemone in TAG with a muscular sphincter similar to that observed in the present study; that specimen was initially considered as a possible different species to M. rimicarivora and P. ingolfi. In the examined material of M. rimicarivora from Snake Pit we have also observed sphincters of different sizes depending on the specimens [some examples of ratio pedal disc diameter measured on the preserved specimens (in mm) / length of sphincter measured on histological sections (in mm) are: 41/6.5, 30.4/ 3.5, and 21.5/3]. In general, the TAG material of M. rimicarivora studied by Fautin & Barber (1999) reached larger sizes than that available for this study from Snake Pit. Thus, in this case, the relative length of the muscular sphincter could depend on the size of the specimen, and its utility as differentiating character should be taken with caution. Fig. 14. Maractis rimicarivora Fautin & Barber, 1989. Preserved specimen (SZ (ANT-2141)). A) Oral view; B) lateral view. Scale bar A-B: 15 mm. AB López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003)238 AB CD 239López-González et al. New records on sea anemones. Zool. Verh. Leiden 345 (2003) With respect to the cnidae types, sizes and distribution, TAG and Snake Pit material agree in all anatomical parts except for the presence (in Snake Pit specimens) of a rathercommon/sporadic cnida present in the actinopharynx and mesenterial filaments. Moreover, this cnida (apparently a microbasic p-mastigophore in which the shaft has a very short V-shaped end) has only been observed in two of the four examined specimens. In our opinion the slight morphological differences between the material examined here from Snake Pit and the original description based on specimens from TAG (Fautin & Barber, 1999) does not justify a separation at specific level. Concluding remarks With the present records included, eight sea anemone species have been reported from hydrothermal vents, two species in the Atlantic [Parasicyonis ingolfi (Snake Pit) and Maractis rimicarivora (TAG and Snake Pit-Elan)], and six species have been found associated with Pacific hydrothermal sites - two of them identified only at generic level - [Actinostola sp., Chondrophellia coronata, Phelliactis sp., Cyananthea hydrothermala (all four species at 12º48’N-103º56’W, 2630-2635 m), Marianactis bythios (Mariana backarc Basin), and Paranthosactis denhartogi (Guaymas Basin)]. Considering the recent collections, four sea anemone species are now known from cold seeps - two of them identified only at generic level - [Monactis vestita (Barbados prism), Stomphia sp. (Monterey Bay), Paractinostola sp. (Monterey Bay), and Hadalanthus aff. knudseni (MAT)]. Doumenc & van Praët (1988) reported the studied material collected during the French Biocyatherm cruise from EPR, 11ºN, 2000 m depth. However, the original files of that cruise place the sampled sites in EPR, 12º48’-49’N-103º56’, 2630-2635 m depth. Taken into account the possible mistake, we have used in the present paper the original sampling data (Desbruyères et al., 1982). According to the opinion of Doumenc & van Praët (1988), not all reported sea anemones could be strictly considered related to hydrothermal sites. This is also applicable to cold seeps. Those species present in the periphery of the vents (such as Actinostola sp., Chondrophellia sp., and Phelliactis sp.) are well known representatives of non-vent deep sea fauna (e.g. Doumenc, 1975). However, other actiniarians locally form dense beds, sometimes placed directly on the chimneys or on oxidized sulphide areas surrounding black smokers (such as Cyananthea hydrothermala, Marianactis bythios, and Maractis rimicarivora). The knowledge of sea anemones in hydrothermal sites and cold seeps is recent, Grassle (1986) reported that sea anemones are common in the vicinity of hydrothermal vents but none has been described yet. During the last 15 years, 12 species have been described (four of them at generic level) from chemoautotrophic environments (7 species from hydrothermal vents and 5 species from cold seeps). Even with the enormous efforts of the deep sea cruises, the number of known species is low in spite of Fig. 15. Maractis rimicarivora Fautin & Barber, 1989. A) cross section at stomodaeum level; B) longitudinal section of the marginal sphincter; C) cross section of a tentacle; D) detail of the ectodermal longitudinal musculature of a tentacle. Abbreviations: 1, pair of mesenteries of the first cycle; 2, pair of mesenteries of the second cycle; 3, pair of mesenteries of the third cycle; 4, pair of mesenteries of the fourth cycle; em, ectodermal longitudinal musculature; ep, epidermis; ga, gastrodermis; me, mesogloea; sph, sphincter. Scale bars: A, 0.5 mm; B, 2 mm; C, 0.4 mm; D, 0.2 mm. 