Three new northeastern Pacific species of the deep-sea limpet family Neolepetopsidae are described. One (Paralepetopsis tunnicliffae) is from the hydrothermal vent habitat, and two (Paralepetopsis clementensis and Neolepetopsis nicolasensis) are from whale bone. This is the first record of the genus Paralepetopsis from the eastern Pacific, and the first record of the family from whale bone, in contrast to all previous records from hydrothermal vents and seeps. The family Neolepetopsidae joins the cocculiniform Pyropeltidae in its occurrence in the vent/seep habitat and the whale-fall habitat. Unlike the Pyropeltidae, in which species may occur in both the vent/seep and the whale-fall habitat, the two new neolepetopsid species in the whale-fall habitat are not the same as the species in the nearest vent/seep habitats.

A taxonomic review of the two genera of the family Alvinocarididae (Decapoda: Caridea), Rimicaris Williams and Rona, 1986 and Chorocaris Martin and Hessler 1990, is presented based on study of type materials and/or supplemental material from recent collections. Two species of Rimicaris, R. exoculata Williams and Rona 1986 and R. kairei Watabe and Hashimoto 2002, and three species of Chorocaris, C. chacei Williams and Rona 1986, C. vandoverae Martin and Hessler 1990, and C. paulexa Martin and Shank 2005, are recognized. All species are exclusively associated with deep-water hydrothermal community. Close relationship between the two genera is confirmed by morphological characters, but the monophyly of Chorocaris is not corroborated. An examination of a good series of material from the Mid-Atlantic Ridge shows that juveniles of Rimicaris exoculata can be arranged in four sequential ontogenetic stages based on morphology. A dramatic change occurs at the size of 7.0 to 9.0 mm in the carapace length. The synonymies of Iorania concordia Vereshchaka 1996 and Rimicaris aurantiaca Martin, Signorovitch & Patel 1997 with Rimicaris exoculata, indicated from molecular evidence by Shank et al. (1998), are confirmed. Morphological differences between R. exoculata and R. kairei and those among C. chacei, C. vandoverae, and C. paulexa, are reassessed.

Lepetodrilid limpets are common inhabitants of deep-sea hydrothermal vents worldwide, but the frequent occurrence of morphologically cryptic species makes their identification very difficult. To facilitate these identifications, we provide DNA barcodes based on ∼1,000 bp of cytochrome-c-oxidase subunit I (COI), for 20 taxa within the genus Lepetodrilus. The method was also used to identify lepetodrilids that were found living on vent decapods. A preliminary phylogenetic analysis resolved relationships among members of several cryptic species complexes; however, COI sequences alone were unable to resolve higher-level systematic relationships caused by saturation of synonymous nucleotide substitutions.

The “Bathymodiolus” childressi group is the most geographically diverse assemblage of deep-sea mussel species. In this paper we consider several possible hypotheses to explain the present biogeographic distribution of the “B.” childressi species complex. Mussels were collected for the first time from mud volcanoes in the Gulf of Cadiz (NE Atlantic Ocean) during the training through research (TTR) 16 research expedition in 2006. Preliminary observations of the shell features indicate that they belong to the “B.” childressi species complex, which has been recognized as morphologically and genetically distinct from other Bathymodiolus species. Molecular analyses of two mitochondrial genes (COI-5 and ND4) were used to characterize the new mussel population from the Gulf of Cadiz (GOC) and to determine their phylogenetic relationships with other members of the “B.” childressi group. The results indicate that the GOC mussels are conspecific with “Bathymodiolus” mauritanicus Cosel (2002), described from West Africa margin, and support a previous hypothesis that “B.” mauritanicus is an amphi-Atlantic species

This paper provides a review of relevant literature concerning the vent crab Bythograea thermydron. This body of work describes a crab species that shares fundamental biological characteristics with typical shallow-water brachyuran crabs, yet possesses a suite of highly evolved traits specific for life at hydrothermal vents. Bythograea thermydron is one of only six known species of Bythograea and is very abundant at vent sites along the East Pacific Rise. Because of the large amount of scientific work at this location, almost everything known about bythograeid vent crabs is based on studies of this single species. This review specifically deals with biogeography, systematics, and evolution; morphology, physiology and special adaptations; ovarian development; mating, brooding, and hatching; and larval biology and dispersal. The various sections emphasize comparisons with shallow-water crabs and highlight characteristics such as: (1) the unique eye structure in the adult stage, which is adapted for sensing the exceptionally dim light that is generated by the vents themselves; (2) the extreme tolerance of adults and juveniles to conditions of low oxygen and high sulfides; (3) the exceptional eurythermal character of juvenile and adult physiology; and (4) the seasonality of ovarian development and subsequent reproductive activity. Discussion of larval biology presents various scenarios of larval dispersal and recruitment back to the vent sites.

The vent shrimp Rimicaris exoculata thrives around many hydrothermal vent sites along the Mid-Atlantic Ridge (MAR), where it aggregates into dense swarms. In contrast to hydrothermal vent fields at the East Pacific Rise (EPR), where the biomass is dominated by tubeworms, clams, and mussels, this shrimp is one of the major animal species at MAR vents. These animals are found in the dynamic mixing interface between cold oxygenated seawater and hot, reduced hydrothermal vent fluid. The adaptation of this shrimp to the hostile deep-sea hydrothermal environment and its survival strategy has been investigated since their discovery at the TAG site in the late 1980s. Rimicaris exoculata is now known to colonize black smoker complexes along the MAR in the depth-range of 2,300–3,900 m (Rainbow, Broken Spur, TAG, Snake Pit, Logatchev, 5°S (Rimicaris cf exoculata). Although the presence of the Rimicaris genus was first believed to be restricted to the MAR, a related species, Rimicaris kairei, was found recently at the Central Indian Ridge (CIR) (Edmonds and Kairei vent field). This review summarizes the current knowledge of Rimicaris shrimp, focusing on their spatial and temporal distribution, chemical and thermal environment, as well as on possible nutrition strategies and behavioral aspects. Recent studies suggested that iron oxide encrusted bacteria hosted in the branchial chamber of R. exoculata from the Rainbow vent field (MAR) might rely on iron oxidation. Striking results on the occurrence and morphology of iron precipitates, as well as on bacterial-mineral interaction in the gill chamber, have lead to the hypothesis of an iron-based symbiosis between bacteria and the shrimp. Special attention is called to these issues.

Species of the neomenioid aplacophoran genus Helicoradomenia Scheltema & Kuzirian are found only in areas of hydrothermal vents, oceanic ridges, and back-arc basins and have been collected widely in the East Pacific, Southwest Pacific, and the Triple Junction in the Indian Ocean, but not in the Atlantic. As with other vent taxa, species diversity of Helicoradomenia in the East Pacific is greatest south of the subduction zone of the Pacific Plate under the North American Plate, which divided the ridge system into two sectors during the Eocene: the northern Juan de Fuca system and southern East Pacific Rise. Diversity of Helicoradomenia species reflects, in smaller numbers, the diversity of the vent limpets in the two sectors. Two Helicoradomenia sister species are illustrated with the characters that separate them, H. juani Scheltema and Kuzirian (1991) from the northern sector and H. acredema Scheltema (2000) from the southern. They apparently speciated when the vicariant event of subduction of a once continuous ridge occurred.

Mussels in the genus Bathymodiolus host endosymbiotic bacteria in their gills, from which the mussel derives much of its nutrition. Bathymodiolin mussels also have functional digestive systems and, as in shallow-water mytilid mussels, cells of the digestive diverticulae are of two types: basophilic secretory cells and columnar digestive cells. Cellular contents of secretory and digestive cells of Bathymodiolus thermophilus and Bathymodiolus brevior from deep-sea hydrothermal vents are comparable to cellular contents of these cell types observed in shallow-water mytilids. In the seep mussel Bathymodiolus heckerae, cellular contents of columnar cells were anomalous, being dominated by an unknown cellular inclusion herein called spherical inclusion unknown or SIX. SIX was observed in all digestive cells and some basophilic cells of B. heckerae examined with TEM. It is a large (2–10-μm diameter) and abundant (7 ± 1.5 inclusions per epithelial cell section) inclusion, with a double external membrane and stacked internal lamellae. No microbial DNA was detected in digestive tubules of B. heckerae using molecular probes, preferential DNA amplification techniques, or DAPI staining, suggesting that SIX is not a unicellular parasite or symbiont. The ubiquity and abundance of SIX within cells of the digestive diverticula suggest that it has an important cellular function (positive or negative), yet to be determined.

The gametogenic biology is described for seven species of gastropod from hydrothermal vents in the East Pacific and from the Mid-Atlantic Ridge. Species of the limpet genus Lepetodrilus (Family Lepetodrilidae) had a maximum unfertilized oocyte size of <90 μm and there was no evidence of reproductive periodicity or spatial variation in reproductive pattern. Individuals showed early maturity with females undergoing gametogenesis at less than one third maximum body size. There was a power relationship between shell length and fecundity, with a maximum of ∼1,800 oocytes being found in one individual, although individual fecundity was usually <1,000. Such an egg size might be indicative of planktotrophic larval development, but there was never any indication of shell growth in larvae from species in this genus. Cyathermia naticoides (Family Neomphalidea) had a maximum oocyte size of ∼120 μm and a fecundity of <400 oocytes per individual. Rhynchopelta concentrica (Family Peltospiridae) had a maximum oocyte size of 184 μm and a fecundity <600, whereas in Eulepetopsis vitrea (Family Neolepetopsidae) maximum oocyte size was 232 μm with a fecundity of <200 oocytes per individual. In none of these three species was there any indication of episodicity in oocyte production. From our observations we support the paradigm that there is no reproductive pattern typical of vent systems but is more related to species' phylogeny.

Our study describes the extraordinary capability of the endosymbiont-bearing bivalve Lucinoma aequizonata to tolerate environmental anoxia. The clam survives without oxygen for 262 days (50% mortality). The total quantity of glycogen in a specimen does not decrease significantly after long-term anoxia (10.5 mo). Common glycogen-derived anaerobic products (opines, lactate, succinate, acetate, and propionate) are only produced in minor quantities. This indicates either severe metabolic depression or the utilization of alternative energy sources. We have found indications that the endosymbiotic bacteria might function as an important carbon source for the bivalve. Transmission electron microscopy studies showed that the symbionts are largely degraded after L. aequizonata was incubated anoxically for 10.5 mo. Polyphosphates detected in symbiont granules by energy dispersive X-ray spectrometry (EDX) might represent an alternative energy source for the clam's metabolism under this stress situation.

Molecular phylogenetic analyses revealed no evidence for cospeciation between deep-sea bathymodiolin mussels (Bivalvia: Mytilidae) and their associated thiotrophic (sulfur-oxidizing) bacterial endosymbionts. Host and symbiont tree topologies were not congruent and inferred time-depths of the gene trees were inconsistent, as expected if the mussel hosts are infected by local strains of the symbiont. Evolutionary divergence among the thiotrophs is correlated with geographical distances among sample locations. Apparently these bacteria established a global distribution long before contemporary oceanic barriers achieved their current positions, and before evolutionarily younger mussel hosts diversified into presently recognized species.

Abundant bacteria have been found on the abfrontal regions of the gill filaments of three species of small mussels from a variety of habitats: Idas washingtoniana and Adipicola sp. from hydrothermal vents on the Juan de Fuca Ridge; Idas simpsoni from a whale skull and from oily drill cuttings in the North Sea. The ultrastructure of their gills and of the associated bacteria is described and illustrated. The Adipicola species differs from the two species of Idas in having bulkier gills and a thicker layer of bacteria, with tighter retention of the symbionts under stalked clusters of microvilli. In both genera the symbionts are superficial, similar to the situation in some Thyasiridae, but unlike the enclosed symbioses of Bathymodiolus species, Lucinidae or Vesicomyidae. The bacterial ultrastructure indicates thiotrophic rather than methylotrophic metabolism in each case. The habitats and food sources of these small mussels are discussed and it is suggested that absorption of dissolved organic compounds may play a part in their nutrition in some circumstances.

Efforts to determine the utilization of Gulf of Mexico (GOM) chemosynthetic production by benthic predators have relied on stable isotope differences between photosynthetic and chemosynthetic production. Whereas the photosynthetic δ¹³C value in GOM surface waters is relatively uniform, chemosynthetic production may differ in different areas depending on prevalence of thiotrophy versus methanotrophy and inorganic carbon source. In this paper we compare the δ¹³C and δ¹⁵N signatures of the symbiont-containing mussel, Bathymodiolus childressi Gustafson, 1998, from four different chemosynthetic sites to test the hypothesis that methanotrophic production results in significant differences among them. Bathymodiolus childressi from two areas characterized by brine seepage and biogenic methane (GC425 and GC233) had very low δ¹⁵N (−3.7‰ and −16.6‰) and δ¹³C (−57.5‰ and −63.5‰) relative to areas with substantial thiotrophic production (GC234 and GC185). Bathymodiolus childressi from each chemosynthetic community had significantly different δ¹³C, and three of the sites also had distinct δ¹⁵N values. The δ¹³C and δ¹⁵N signatures of hagfish (Eptatretus sp.) and giant isopods (Bathynomus giganteus) captured from two sites showed little or no chemosyntheic usage. Squat lobsters (Munidopsis sp.) showed heavy incorporation of chemosyntheic production, but did not directly consume B. childressi.

The continental slope of the Gulf of Mexico supports dense aggregations of tubeworms and mussels that have symbiotic chemoautotrophic bacteria. Associated with these communities are numerous heterotrophic fauna and free-living bacteria. Here we examine the stable C, N, and S isotope compositions of fauna from two chemoautotrophic communities to identify isotope ranges of chemoautotrophic primary production and determine the usage of that primary production by heterotrophic invertebrates. The range in isotope values of the chemoautotrophic production is different between sites. A brine seep (GC233) dominated by mussels symbiotic with methanotrophic bacteria has ¹³C and ¹⁵N depleted nutrient sources (−50 to −65‰ and −9 to −12‰, respectively), indicating methanotrophy using biogenic methane and suggesting ammonium as the dominant nitrogen source. However, those same sources were ³⁴S-enriched (6‰–11‰), as indicated by resident heterotrophs (Munidopsis sp., Methanoaricia dendrobranchiata Blake 2000, Alvinocaris stactophila Williams 1988, Phascolosoma turnerae Rice 1985), indicating that thiotrophy was a minor chemosynthetic method at the site. A site dominated by tube worms and mussels (GC234) has two isotopically distinct sources of carbon, one between −24 and −30‰ and another of approximately −40‰, as indicated by the resident heterotrophs. Resident heterotrophs at GC 234 had δ¹⁵N and δ³⁴S values from 1‰ to 5‰ and −10‰ to 6‰, respectively. These isotope values suggest a mix of thiotrophy and methanotrophy (largely from thiotrophic sources) at the site. We estimate that hagfish (Eptatretus sp.) captured approximately 2 km from the communities derived at least 10% of their carbon from chemoautotrophic sources because of low δ¹³C values. In contrast, giant isopods (Bathynomus giganteus Milne Edwards, 1879), captured with the hagfish show negligible incorporation of chemosynthetic production.

Carbon fixation by sulfur-oxidizing chemosynthetic bacteria forms the base of the food chain in deep-sea (diffuse-flow) hydrothermal vent ecosystems. Temperature and the availability of oxygen and reduced sulfur are believed to be factors that contribute to the structure of hydrothermal vent communities. Sulfur concentration and speciation can change rapidly as highly reducing vent fluids mix with cold oxygenated seawater, thus the path followed by source water before passing over organisms hosting sulfur-oxidizing endosymbionts may have important implications for these animals. Here we show an apparent correlation between the zonation of symbiont-containing species and the sulfur chemical speciation (sulfide, polysulfides, thiosulfate) in the water bathing them. We also report in-situ measurements of thiosulfate (S₂O₃ ²⁻) in hydrothermal fluids, predominantly in the area inhabited by the mussel, Bathymodiolus brevior. These results provide field evidence of environmental levels of thiosulfate that may be capable of supporting thiosulfate-utilizing symbionts at hydrothermal vents. The three dominant shellfish species were arranged concentrically in a distinct bull's eye pattern at our study site. Alviniconcha sp. 1 snails inhabited the central, most reducing sulfide-rich zone, Ifremeria nautilei snails formed a thin band surrounding the Alviniconcha, and B. brevior mussels were farthest away from the source fluid in the most oxidized region. After removal of many of the Alviniconcha, some I. nautilei moved into the vacated space, whereas the B. brevior remained around the extreme periphery of the area impacted by the diffuse flow. These results suggest that diffuse flow chemistry is one of the key parameters affecting organism distribution.

Between October 2005 and March 2006, a seafloor volcanic eruption occurred at 9°50′N East Pacific Rise (EPR), establishing a “time zero” for characterizing newly-formed hydrothermal vent habitats and comparing them to pre-eruption habitats. Before the eruption, mussels (Bathymodiolus thermophilus) formed large aggregates between 9°49.6′ and 9°50.3′N. After the eruption, the few mussels remaining were in sparsely-distributed individuals and clumps, seemingly transported via lava flows or from mass wasting of the walls of the axial trough. In situ voltammetry with solid state gold-amalgam microelectrodes was used to characterize the chemistry of vent fluids in mussel habitats from 2004 to 2007, providing data sets for comparison of oxygen, sulfide, and temperature. Posteruption fluids contained higher sulfide-to-temperature ratios (i.e., slopes of linear regressions) (10.86 μM °C⁻¹) compared with pre-eruption values in 2004 and 2005 (2.79 μM °C⁻¹ and −0.063 μM °C⁻¹, respectively). These chemical differences can be attributed to the difference in geographic location in which mussels were living and physical factors arising from posteruptive fluid emissions.

In April 1991, submarine volcanic eruptions initiated the formation of numerous hydrothermal vents between 9°45′ and 9°52′N along the crest of the East Pacific Rise (EPR). Dramatic changes in biological community structure and vent fluid chemistry have been documented throughout this region since the eruptive event. By April 2004, mussels (Bathymodiolus thermophilus) dominated the faunal assemblages at several of the vent sites formed during of after the 1991 eruptions, whereas other habitats within the region were dominated by the vestimentiferan Riftia pachyptila. In the present paper, we build upon the extensive data sets obtained at these sites over the past decade and describe a manipulative experiment (conducted at 9°49.94′N; 104°14.43′W on the EPR) designed to assess interrelationships between vent fluid chemistry, temperature, biological community structure, and seismic activity. To this end, in situ voltammetric systems and thermal probes were used to measure H₂S/HS⁻ and temperature over time in a denuded region of an extensive mussel bed in which an exclusion cage was placed to inhibit the subsequent migration of mussels into the denuded area. Fluid samples were taken from the same locations to characterize the associated microbial constituents. Basalt blocks, which were placed in the cage in April 2004 and subsequently recovered in April 2005, were colonized by more than 25 different species of invertebrates, including numerous vestimentiferans and remarkably few mussels. Recorded temporal changes in vent fluid chemistry and temperature regimes, when coupled with microbiological characterization of the vent fluids and seismic activity data obtained from ocean bottom seismometers, shed considerable light on factors controlling biological community structure in these hydrothermal ecosystems.

In 1993 and 1994, the shelf and slope experimental taphonomy initiative (SSETI) deployed shells of a suite of molluscan species in a range of environments of deposition (EODs) representing a range of depths, sediment types, and environmental conditions with the goal of measuring taphonomic rates over an extended period of time. In 1999 and 2001, SSETI retrieved skeletal remains from 41 locations in the Bahamas and on the Gulf of Mexico continental shelf and upper slope that had been on the seafloor for eight years. Here, we compare taphonomic processes in two different ocean basins, across 24 environments of preservation (EOP) to evaluate the influence of species, sedimentary environment, degree of burial, and water depth on the preservational process. Taphonomic signature after eight years was almost exclusively a function of location of deployment and, frequently, taphonomically-distinctive locations of deployment were subsumed within distinctive EODs. EOD-level characteristics were insufficiently discriminative to delineate environments of preservation. EOPs and EODs are not synonymous concepts. Across all sites and species, the dominant taphonomic process was discoloration. Dissolution was of penultimate importance; nevertheless the cumulative impact over eight years was insufficient to produce a significant loss in shell weight in any EOP. Maximum dissolution intensity was normally observed on the outer shell surface; the inner and outer shell surfaces are inherently different in their time course of shell deterioration. Principal components analysis (PCA) demonstrated limited co-occurrence of discrete taphonomic processes among the 24 EOPs. Breakage and edge rounding fell on the same PCA axis, but these two processes were independent of all others. PCA divided dissolution into three independent components that discriminated the inner and outer shell surface of bivalves (and spire and body whorl of gastropods) and pitting from the development of a chalky surface. Discoloration was dissembled into five distinctive discoloring processes: fading without subsequent discoloration, the development of a brown-to-red coloration, orange/orange mottled discoloration, development of a green/green mottled color, and gray-to-black discoloration. The only concordance of ostensibly distinctive taphonomic processes was the association of small pits on the shell surface with orange discoloration on the shell. Depth did not exert a single significant effect on any of the eight primary taphonomic factors resolved by PCA, likely because of burial processes. The trends in taphonomic signature cannot be explained by any simple combination of sediment type and degree of exposure. A comparison between two-year and eight-year deployments suggests that important revelations can be gleaned from short-term experimental deployments, yet the same comparison discloses the spuriousness of other inferences. Thus, long-term experiments are essential to understand the time course of preservation. The taphonomic process is, in general, slow, and nonlinearity in rates over time constrains the subset of inferences that can be deduced accurately from short deployment periods.

Unusually fine preservation of soft anatomy in the fossil record, often referred to as Lagerstätte deposits, has led to great advances in understanding the evolution of life. An understanding of the potential environments of deposition that might lead to exquisite preservation may help to reconstruct the effects of the taphonomic filter and thereby better interpret the completeness of fossil Lagerstätten. Seafloor brines are potential environments leading to exceptional preservation. The Shelf and Slope Experimental Taphonomy Initiative (SSETI) placed mollusc shells, decapod crustaceans, sea urchins, and wood into a Gulf of Mexico seafloor brine pool environment to study the rates and modes of skeletal and soft tissue decay. We found that skeletons, soft tissue, and wood placed directly in the sulfidic anoxic brine were essentially not degraded or discolored over nearly a decade. Where the brine mixed with overlying seawater in a brine stream, the taphonomic signature was quite different. Calcium-carbonate shell and urchin tests underwent severe dissolution, whereas terrestrial plant remains were unaltered. Farther from the brine, shell and urchin carbonate was only slightly dissolved, wood was completely consumed by xylophagus animals, and decapods were reduced to claw parts only. From these experiments, we conclude that the taphonomic signature of a brine seep can be recognized by a unique juxtaposition of preservation styles that varies across phyla. The central area of the anoxic brine would promote exquisite preservation of carbonate, soft-animal tissue, and cellulose. The central area would be ringed by a zone of near total loss of shell carbonate, but paradoxically would promote the preservation of organic tissue such as shell periostracum and ligament, wood, nuts, and cones. Where seawater salinity is normal, the taphonomic signature would return to a seafloor assemblage appropriate to the depth and depositional environment. Brine seep systems may provide a mechanism for maintaining unaltered organism remains at the sediment-water interface long enough to become buried with soft anatomy intact and undisturbed. The very important fossil deposit known as the Burgess Shale exhibits preservation styles and patterns that might be explained by presence of brine. Our experimental work in a modern brine system may shed some light on the taphonomic conditions that led to preservation known as the “Burgess Shale type.”

Protein metabolism is an expensive cellular process that can generally account for one third of basal metabolism in animals. Shifts in the stability of proteins under increased environmental temperatures could potentially alter the energy budget of an organism. However, studying the thermal stability kinetics of individual proteins is tedious and ultimately, difficult to relate to changes in the fitness of an organism. Yet understanding how organisms inhabiting extreme environments (polar seas, hydrothermal vents, and deep ocean basins) are able to maintain or limit the rate of protein turnover in the total cellular protein pool is crucial for our understanding of the total metabolic costs associated with survival in these habitats. To assess protein stability in field collected organisms at a proteome scale, we developed a high-throughput assay for protein denaturation profiles of total tissue extracts in bivalves. These profiles are quantitative and reveal unique compositional features of different tissues. Heat stress experiments in the clam Mercenaria mercenaria reveal that the protein pool of mantle and digestive mass tissues are more thermally stable after a short exposure to 35°C. This increase in stability could have large implications for the energy budget of M. mercenaria when exposed to high summer water temperatures. This methodology could readily be used to assess the stability and/or turnover potential of a variety of organisms experiencing extremes of both temperature and pressure.