The shallow-water hydrothermal system of Punta Mita in Banderas Bay is located on the fault called Fisura de las Coronas off Punta Pantoque beach. In this area, three sites with hydrothermal vents were studied at a depth of 9 m. This study aimed to characterize the structure of the benthic infauna communities that coexist in this hydrothermal system; therefore, physicochemical parameters were measured and the organisms found in the sediment samples were identified up to the class taxonomic level. The highest temperatures (89°C) were recorded within the hydrothermal influence area, which was reflected in an inverse relationship with pH, conductivity and salinity. Sediment temperature profiles increased at greater depth. A total of 371 individuals were found and these were grouped into eight classes: Malacostraca, Maxillopoda, Gastropoda, Bivalvia, Scaphopoda, Polychaeta, Leptocardii and Stenolaemata. The Malacostraca class was the most abundant with 240 individuals, while the Scaphopoda was the lowest with 3. The organic matter contents in the sediments were higher in the areas adjacent to the hydrothermal activity. The high temperature of the hydrothermal discharges structures the benthic community since it was the factor that differed most significantly in the study sites, causing lower abundances in the area of hydrothermal influence compared with the more distant areas. Despite the above, it is concluded that the benthic community of the area with hydrothermal activity is part of the community adjacent to this influence, only in lower numbers.

We present the first record of the very large deep-sea mytilid Gigantidas horikoshii Hashimoto & Yamane, 2005 outside of its type distribution, based on a juvenile specimen collected by fishermen at the Tashi fishing grounds east of Taiwan. This record extends the distribution of the species in about 20 latitudinal degrees to the west (about 1916 km), and it is the first record for this species outside the Izu-Ogasawara Island-arc, southern Japan, representing the westernmost geographic limit of this species and the first record in Taiwanese waters.

Hydrogen cyanide (HCN) is considered a fundamental molecule in prebiotic chemistry experiments due to the fact that it could have an important role as raw material to form more complex molecules, as well as it could be an intermediate molecule in chemical reactions. However, the primitive scenarios in which this molecule might be available have been widely discussed. Hydrothermal systems have been considered as abiotic reactors and ideal niches for chemical evolution. Nevertheless, several experiments have shown that high temperatures and pressures could be adverse to the stability of organic molecules. Thus, it is necessary to carry out systematic experiments to study the synthesis, stability and fate of organic molecules in hydrothermal scenarios. In this work, we performed experiments focused on the stability and fate of HCN under a simple hydrothermal system scenario: the thermolysis of HCN at 100°C, at acidic and basic pH and in the presence of Mg-montmorillonite. Furthermore, we analysed the products from HCN thermolysis and highlighted the role of these chemical species as prebiotic molecules under a hydrothermal scenario.

Aggregates of the Polychaeta Phyllochaetopterus socialis were recorded for the first time off Gemlik Bay in the Sea of Marmara, in August 2008. These were found at about 53 m depth, on the soft sediments around the sub-sea part of the North Anatoly Earthquake Fault. Samples were landed by beam trawl. Total wet weight of the mats was 58 kg. Forty-three species belonging to 10 phyla associated with P. socialis were recorded from the whole landing materials. Echinodermata and Gastropoda were the most abundant (12 and 8 species, respectively). Shannon–Wiener diversity and Margalef species richness indices were applied to analyse the structure of benthic communities. Presence and abundance lognormal distribution of the species and communities in mat habitat are shown. The hydrographic environment of the water mass is also discussed.

A new species of the hippolytid shrimp genus Lebbeus White, 1847 is described from the Von Damm Vent Field (VDVF) on the Mid-Cayman Spreading Centre, Caribbean Sea, at 2294 m water depth. Lebbeus virentova sp. nov. is defined and illustrated from seven specimens, with brief notes on its distribution and habitat. Molecular phylogenetic data from the COI mDNA region are used to analyse the species’ phylogenetic position, and its morphology is compared with previously described species. This new species represents the second family of caridean shrimp to be reported from the VDVF. Lebbeus virentova sp. nov. is the eighth member of the genus to be described from hydrothermal vents and appears to be the first hippolytid shrimp at a vent field known from outside the Pacific Ocean.

Iheyaspira bathycodon sp. nov. is described from the Von Damm Vent Field on the world's deepest spreading centre, the Mid-Cayman Spreading Centre (MCSC), Caribbean, at 2300 m depth. The new species is defined and illustrated from 11 specimens, with brief notes on habitat and known distribution. Molecular phylogenetic data from partial COI mDNA, 16S rDNA and nuclear 18S rDNA regions are used to analyse the species’ phylogenetic position and its morphology is compared with previously described skeneid and vent taxa. The new species is distinguished from the most closely allied vent species, Iheyaspira lequios Okutani, Sasaki & Tsuchida, 2000 by morphological differences in radula diagnosis and appendage structure of the head-foot. Iheyaspira bathycodon sp. nov. is the tenth turbinid to be described from a hydrothermal-vent environment and the second species to be named from recently discovered hydrothermal vents on the MCSC. Determining the faunal composition of assemblages at the vent fields of the MCSC will help to elucidate the vent biogeography of the region.

Rimicaris hybisae sp. nov. is described from hydrothermal vent fields on the world's deepest seafloor spreading centre, the Mid-Cayman Spreading Centre (MCSC), Caribbean, at depths of 2300–4960 m. The new species is described and illustrated on the basis of 17 specimens. Brief notes on the distribution and habitat of the new species are provided. Molecular phylogenetic data from mitochondrial COI (460 base pair (bp)), 16S ribosomal RNA (549 bp) and nuclear 18S ribosomal RNA (576 bp) regions is used to complement the description. Morphological variation within R. hybisae sp. nov. and morphological affinities with previously described species are discussed. Based on morphological and molecular evidence, the new species is provisionally assigned to the genus Rimicaris, and differs from all known species in the genus by a distinctive pair of ‘pores' on the posterior lobes of its four-lobed dorsal organ. An emended diagnosis for Rimicaris is provided. Rimicaris hybisae sp. nov. is the first taxon to be described from MCSC vent fields. This record extends the known geographical range of Rimicaris into the Caribbean Sea and constitutes the deepest documented occurrence of alvinocaridid shrimp.

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.

The parapagurid hermit crab, Paragiopagurus ventilatus, is reported from hydrothermal vents on the Nikko Seamount, Mariana Trough, at a depth of 410 m. This is the first record of this species outside Taiwan, and represents a major range extension. The animals were found using empty tubes of the siboglinid worm Lamellibrachia satsuma for housing, representing the first example of this carcinoecium for a hermit crab. However, it was observed that some of them changed their housing to gastropod shells during rearing in aquaria. Originally, this species was reported to use gastropod shells for housing. It is considered that the use of siboglinid tubes is due to necessity rather than preference, because empty gastropod shells are very scarce in the collection site.

A new species of the palaemonid shrimp genus Periclimenes, P. cannaphilus, is described from upper bathyal hydrothermal vents of the Bonin-Mariana Arc in the north-western Pacific at depths of 392–456 m. A symbiotic relationship between the new shrimp species and a siboglinid tube worm Lamellibrachia satsuma is suggested by their simultaenuous collection and further observations in situ. Similarities in the morphology and symbiotic association suggest that the new species is closely related to P. thermohydrophilus, also associated with L. satsuma in shallow hydrothermal vent fields in Kagoshima Bay, southern Japan, but differences in the rostral shape, the position of the epigastric tooth on the carapace, and the development of the hepatic tooth on the carapace morphologically differentiate the two species. Phylogenetic analysis based on sequences of the mitochondrial DNA COI gene supports the recognition of two clades corresponding to these two taxa.

Using a morphology-based approach, we explore the relationships between three poorly understood species of organic-walled Foraminifera. Thalmann and Bermudez (1954) described Chitinosiphon rufescens as the type species of a new monotypic genus which they compared to the tubular agglutinated foraminiferan Bathysiphon. Loeblich and Tappan (1964), however, considered C. rufescens to be identical to Reophax membranacea Brady 1879, type species of another organic-walled genus, Nodellum. Based on a re-examination of the type specimens of both species, new material of C. rufescens from the Lost City hydrothermal field, and new material of N. membranacea from the NE Atlantic and Pacific Oceans, we show that these two deep-sea species are distinguished by the following features. (1) Chitinosiphon rufescens lacks the distinct, regular constrictions that divide the tubular test of N. membranacea into a series of segments. (2) The proloculus is spindle-shaped in C. rufescens but sub-cylindrical in N. membranacea. (3) A distinctive, pocket-like invagination is developed at the base (proximal end) of the proloculus in N. membranacea but not in C. rufescens. However, a series of undescribed species which occur in deep-sea sediments blur the distinction between the two genera. We therefore adopt a conservative position and regard Chitinosiphon as a junior synonym of Nodellum. We also examined the holotype and new material of Nodellum moniliforme Resig, 1982, the type species of Resigella Loeblich and Tappan, 1984, in which the organic-walled test comprises a series of bulbous chambers. This species exhibits a basal invagination, identical to the feature present in Nodellum membranacea. These three remarkable species are united by the basically tubular test and the nature of the test wall which is largely organic, brownish in colour, and exhibits no internal structure when broken sections are examined by SEM. The surface of the organic test of Nodellum rufescens from Lost City is strewn with tiny (≤1 μm), needle-shaped mineral particles, visible only by SEM. More equidimensional, micron-sized particles are present in the other two species. We agree with Thalmann and Bermudez (1954) that N. rufescens is related to tubular agglutinated taxa such as Bathysiphon. Resigella may have similar affinities, although this needs to be tested using molecular approaches.

Deep-sea hydrothermal vents display extreme and highly variable environmental conditions that are expected to be among the most important factors structuring associated benthic populations and communities. We tested this assumption, focusing on the distribution of gastropods, as well as on the demographic population structure and reproductive biology of one dominant gastropod species in zones characterized by alvinellid polychaetes and vestimentiferan tubeworms. A total of 14 biological samples from both types of habitats were collected at three sites on the East Pacific Rise 13°N vent field in May 2002. At all vents except one, the physico-chemical environment was described in two steps: (1) pH, total sulphide and reduced iron concentrations have been measured in situ in Alvinella habitats and correlations to temperature were assessed at the scale of each sampled vent; and (2) assuming the consistency of these relationships within a single edifice, ranges of physico-chemical factors were estimated for each biological sample from the corresponding fine scale temperature measurements. A total of 11 gastropod species were identified from all samples and 2 main faunal assemblages were distinguished: one dominated by Lepetodrilus elevatus in the alvinellid zone as well as in the vestimentiferan zone, and one dominated by the peltospirids Nodopelta heminoda, N. subnoda and Peltospira operculata confined to the alvinellid zone. Peltospirid gastropods were dominant over lepetodrilid gastropods in the more acidic, sulphide-richer, and hotter environments. Although this pattern could be related to specific physiological tolerances to temperature and sulphide toxicity, the weak correlation between community structure and physico-chemical variables suggests that additional factors are also involved. Particularly, the low species richness and the overwhelming dominance of L. elevatus in one faunal assemblage suggest that this species may outcompete peltospirids and greatly affect community structure. This hypothesis is supported by large differences in the demographic structure and reproductive biology of L. elevatus between the 2 faunal assemblages.