Infaunal Life Research Articles

Clam Genome and Transcriptomes Provide Insights into Molecular Basis of Morphological Novelties and Adaptations in Mollusks

Bivalve mollusks, comprising animals enclosed in two shell valves, are well-adapted to benthic life in many intertidal zones. Clams have evolved the buried lifestyle, which depends on their unique soft tissue structure and their wedge-shaped muscular foot and long extendible siphons. However, molecular mechanisms of adaptative phenotype evolution remain largely unknown. In the present study, we obtain the high-quality chromosome-level genome of Manila clam R. philippinarum, an economically important marine bivalve in many coastal areas. The genome is constructed by the Hi-C assisted assembly, which yields 19 chromosomes with a total of 1.17 Gb and BUSCO integrity of 92.23%. The de novo assembled genome has a contig N50 length of 307.7 kb and scaffold N50 of 59.5 Mb. Gene family expansion analysis reveals that a total of 24 single-copy gene families have undergone the significant expansion or contraction, including E3 ubiquitin ligase and dynein heavy chain. The significant expansion of transposable elements has been also identified, including long terminal repeats (LTR) and non-LTR retrotransposons. The comparative transcriptomics among different clam tissues reveals that extracellular matrix (ECM) receptors and neuroactive ligand receptors may play the important roles in tissue structural support and neurotransmission during their infaunal life. These findings of gene family expansion and tissue-specific expression may reflect the unique soft tissue structure of clams, suggesting the evolution of lineage-specific morphological novelties. The high-quality genome and transcriptome data of R. philippinarum will not only facilitate the genetic studies on clams but will also provide valuable information on morphological novelties in mollusks.

Deep-sea infauna with calcified exoskeletons imaged in situ using a new 3D acoustic coring system (A-core-2000)

The deep ocean is Earth’s largest habitable space inhabited by diverse benthic organisms. Infauna play crucial roles in shaping sedimentary structures, relocating organic matter, porewater chemistry, and hence biogeochemical cycles. However, the visualization and quantification of infauna in situ inside deep-sea sediment has been challenging, due to their sparse distribution and that deep-sea cameras do not visualize animals living below the sediment surface. Here, we newly developed a 3D acoustic “coring” system and applied it to visualize and detect burrowing bivalves in deep-sea sediments. The in situ acoustic observation was conducted at a dense colony of vesicomyid clams in a hydrocarbon seep in Sagami Bay, Japan, focusing on a patch of juvenile clams with a completely infaunal life style. We clearly observed strong backscatters from the top and lower edges of animals in our 3D acoustic data. At least 17 reflectors were identified in the survey area (625 cm2), interpreted to correspond to living clams. The estimated depths of the lower edge of clams ranged between 41 and 98 mm. The acoustic system presented here is effective for detecting and monitoring infauna with calcified exoskeletons. This novel tool will help us better assess and understand the distribution of deep-sea infauna, particularly those groups with hard exoskeletons, as well as biogeochemical cycles.

High-resolution taphonomy of the Lower Cretaceous “Amargosa Biota”, Central Tucano Sub-Basin, Bahia, Brazil: Implications for the paleoenvironmental dynamics of a new Konservat-Lagerstätte

We report the Amargosa Biota from the middle part of the Lower Cretaceous Marizal Formation (Central Tucano Sub-Basin, NE Brazil), as a new Konservat-Lagerstätte . Exceptionally preserved fossils are confined to the lower part of an up to 15-m-thick, mud-dominated succession, named Amargosa Bed. Seven bedding planes (L0-L6) with distinct sedimentological and taphonomic attributes were identified in the type section (Amargosa Village, Euclides da Cunha County, Bahia State), distributed in an ~1-m-thick succession of well-laminated claystone, mudstone, siltstone, and very fine-grained sandstone. These contain ostracods, spinicaudatan carapaces, palaemonid shrimps, fish, and comminuted plant remains. Fossils occur in high concentration on at least four bedding planes (i.e., L2, L3, L5, and L6), forming polytypical assemblages that are dominated by one of the fossil groups. Assemblages are formed mainly by autochthonous to parautochthonous elements, representing variable, but limited, temporal mixing. A key attribute of some fossil-rich strata (L3, L5, and L6) is the preservation of poorly biomineralized organisms and/or of complete soft-bodied parts, which are typically prone to destruction due to rapid decay or bioturbation. The polytypical nature of these fossil assemblages, interbedded with non-fossiliferous intervals, suggests mass mortality events, probably caused by abrupt changes in water parameters (anoxia, salinity, pH, among others). The dark greenish gray color (yellowish when weathered), and the finely laminated nature of the claystone, siltstone, and mudstone containing members of the Amargosa Biota indicates that the benthic infaunal life was absent or, at least, very scarce in a locally, relatively deep, oxygen-poor lake bottom. Anoxia and high salinity, linked with local semi-arid conditions during the Lower Cretaceous may have played key roles in the exceptional preservation of some fossils (shrimps, fish). Finally, our data provide a more comprehensive understanding of the temporal distribution of taxa and taphonomic processes associated with the complex genesis of the fossil-bearing interval of the Amargosa Bed in its type locality. • A new Aptian Konservat-Lagerstätte is described in NE Brazil; • Fossil-bearing strata reveal complex taphonomic histories; • Triggers are short-term variations in oxygen availability and salinity, coupled with water level fluctuations; • Fossil-rich bedding planes are frozen snapshots of paleocommunities that lived in highly stressed, aquatic system.

Systematics, age, paleoecology and paleobiogeography of Middle to Late Jurassic benthic foraminiferal assemblages from Jumara Dome, Kutch, Gujarat, India

The studied section of the Patcham-Chari formations of Middle to Upper Jurassic rocks exposed at Jumara Dome, Kutch Basin, Gujarat, India yielded rich foraminiferal assemblages comprising 104 species, of which 49 are reported for the first time from the Indian region. The foraminiferal species are systematically described and illustratedwith the help of SEMimaging. The foraminiferal assemblages are used to interpret the age, paleoecology, and paleobiogeography. Although most of the foraminiferal species are rather long ranging, on the basis of a large number of species characteristic of the Bathonian, Callovian and Oxfordian, globally as well as in the Indian region, a Bathonian to Oxfordian age is assigned to the studied sequence. Based on the dominance of the suborder Lagenina, superfamily Nodosariacea, family Vaginulinidiae, calcareous hyaline forms, the genus Lenticulina, high Fisher’s diversity index, morphogroup J2, shallow infaunal life habit, detrivores, bacterial scavengers, and omnivores feeding strategy in the assemblages, a shallow water, near shore, open marine environment ranging from mid- to outer shelf with normal salinity and normal to well-oxygenated waters with high nutrient influx is interpreted for the studied assemblages. The Middle to Late Jurassic Jumara foraminiferal assemblages are assigned to a separate province of the Antiboreal Realm, the Indo-East African Province, located at the southern margin of the Tethyan Realm and transitional between the Tethyan and the Antiboreal realms.

Remnants of ancestral larval eyes in an eyeless mollusk? Molecular characterization of photoreceptors in the scaphopod Antalis entalis

BackgroundEyes have evolved and been lost multiple times during animal evolution, however, the process of eye loss has only been reconstructed in a few cases. Mollusks exhibit eyes as varied as the octopod camera eye or the gastropod cup eye and are ideal systems for studying the evolution of eyes, photoreceptors, and opsins.ResultsHere, we identify genes related to photoreceptor formation and function in an eyeless conchiferan mollusk, the scaphopod Antalis entalis, and investigate their spatial and temporal expression patterns during development. Our study reveals that the scaphopod early mid-stage trochophore larva has putative photoreceptors in a similar location and with a similar gene expression profile as the trochophore of polyplacophoran mollusks. The apical and post-trochal putative photoreceptors appear to co-express go-opsin, six1/2, myoV, and eya, while expression domains in the posterior foot and pavilion (posterior mantle opening) show co-expression of several other candidate genes but not go-opsin. Sequence analysis reveals that the scaphopod Go-opsin amino acid sequence lacks the functionally important lysine (K296; Schiff base) in the retinal-binding domain, but has not accumulated nonsense mutations and still exhibits the canonical G-protein activation domain.ConclusionsThe scaphopod Go-opsin sequence reported here is the only known example of a bilaterian opsin that lacks lysine K296 in the retinal-binding domain. Although this may render the Go-opsin unable to detect light, the protein may still perform sensory functions. The location, innervation, development, and gene expression profiles of the scaphopod and polyplacophoran apical and post-trochal photoreceptors suggest that they are homologous, even though the scaphopod post-trochal photoreceptors have degenerated. This indicates that post-trochal eyes are not a polyplacophoran apomorphy but likely a molluscan synapomorphy lost in other mollusks. Scaphopod eye degeneration is probably a result of the transition to an infaunal life history and is reflected in the likely functional degeneration of Go-opsin, the loss of photoreceptor shielding pigments, and the scarce expression of genes involved in phototransduction and eye development. Our results emphasize the importance of studying a phylogenetically broad range of taxa to infer the mechanisms and direction of body plan evolution.

Environmental Factors Influencing Benthic Polychaete Distributions in a Subtropical Lagoon

AbstractFine-grained organic-rich sediments (FGORS) in the Indian River Lagoon (IRL), Florida, sometimes called “muck,” contain elevated water, silt-clay, and organic matter contents and are abundant as a result of anthropogenic nutrient inputs. Many polychaetes inhabit the benthic sediments of estuaries and tolerate various degrees of FGORS. FGORS composition can be variable, and its effects on infaunal life such as polychaetes may depend upon concentration and composition. The IRL Cox Muck Index (CMI) is proposed as a mechanism for assigning a single value to the complex composition of muck and found to be a useful tool for summary and comparison. CMI has negative correlations with polychaete density (R2 = 0.2, p < 0.001), richness (R2 = 0.57, p < 0.001), and diversity (R2 = 0.55, p < 0.001) based on multiple regression of principle components (PCs) derived from principle components analysis (PCA). Sediment with CMI of <1 fails to meet the definition of IRL muck in at least one parameter and is assumed capable of sustaining some metazoan life. The CMI range of 0.1‐0.2 supports the most robust polychaete community. The polychaete species Diopatra cuprea, Glycera americana, Alitta succinea, and Pectinaria gouldii persisted in the IRL above 0.6 CMI. An environmental dredging project removed muck sediments midway through this study and polychaete recovery following dredging was monitored. At one site, an area of Turkey Creek with abundant muck, the CMI was significantly reduced from 1.4 to 0.8 (p < 0.001). The developing polychaete community at these stations included G. americana and A. succinea. At the end of the study, there were increases in overall polychaete community density, richness, and diversity to 1,000 m−2, S = 3, H = 0.55, respectively.

Hydraulic sediment penetration and seasonal growth of petalonamean basal discs from the Vendian of Ukraine

Around the Ediacaran-Cambrian transition, about 540 million years ago, marine organisms began to dig in the sediment that has resulted in its better ventilation and further expansion of infaunal life. Few vertical infaunal burrows are known from the Precambrian and they are usually attributed to sea anemones. Here we show that the enigmatic Ediacaran petalonamean ‘sea pens’ were able to penetrate sediment for more than one centimetre depth while anchoring the body in the microbial mat. Their growth, as evidenced by numerous well-preserved basal discs from the late Ediacaran Lomoziv Member of the Mohyliv Formation in Podolia, Ukraine, was under control of rhythmic sedimentation events and periodic microbial mat development. Size frequency distribution in classes of both the final disc size and growth retention stages show that their size increase was stepwise. Each discrete stage corresponds to deposition of a thin sediment layer and development of the microbial mat at its top. Podolia was located near the South Pole in the Ediacaran (Vendian) and such rhythmic sedimentation was probably connected with the local climate seasonality.

Differentiation of delta and open marine deposits based on an integrated ichnological and sedimentological analysis of the Late Triassic Nayband Formation, Tabas Block, Central Iran

The palaeoenvironmental significance of trace fossil assemblages in the shallow marine deposits of the Late Triassic Nayband Formation of the Tabas Block, Central Iran has been assessed for the first time. The siliciclastic successions of the Nayband Formation, are highly bioturbated and allow relationships between changes in ichnoassemblages within a depositional system to be documented and placed in a palaeoenvironmental framework. The main purposes of this paper are: (1) to describe and illustrate the trace fossils assemblages of the Nayband Formation; (2) integration of ichnologic and sedimentologic data to evaluate different stress factors on the infaunal communities; and (3) to briefly discuss paleoenvironmental distribution of various trace fossil assemblages in order to differentiate between deltaic and non-deltaic shoreface successions. The Upper Triassic Nayband Formation has been studied and measured in one section, where the Nayband Formation is well accessible and continuously exposed. This section was logged and evaluated using physical sedimentology and ichnology in order to establish a basis for the interpretation of sedimentary processes (facies) and depositional systems. In this study, trace fossils (diversity, abundances, and ethologies) and the spatial arrangement of sedimentary structures are used to further refining the interpretation of environmental parameters such as hydrodynamic energy, water turbidity, substrate properties, food supply, temperature, oxygenation, salinity, and sedimentation rates. Based on facies characteristics and stratal geometries, the siliciclastic succession is divided into two facies associations, fluvial-dominated delta (FA), and open marine (FB). Twenty-eight ichnogenera have been identified in delta and open marine successions: The assemblage is dominated by Rhizocorallium, Thalassinoides, Ophiomorpha, Helminthopsis, Palaeophycus and Skolithos. Their distribution is clearly linked with lithofacies and depositional environments. High rates of fluvial discharge, high water turbidity, seasonally high rates of deposition and phytodetrital pulses in river-dominated deltas may cause marked variations in the temperature, oxygenation and salinity of the fluvial-dominated delta successions. All of these factors in combination lead to impoverishment in trace diversity and reduction in burrow size but to rapid colonization of the substrate by single-layer colonizers of opportunistic deposit feeders. Low ichnodiversity, low bioturbation intensities with highly bioturbated clusters shown by single colonization events by opportunistic, simple feeding strategies of trophic generalists and a paucity of suspension-feeding structures elements represent a “stressed”, non-archetypal Cruziana ichnofacies. The changes of behavioural complexity and the tiering profiles in the offshore-shoreface complex of the Nayband Formation when compared with the river-dominated delta successions represent the transition from epifaunal life habits with simple tiering structures to infaunal life habits with complex tiering pattern. The occurrence of diverse trace fossil suites attributable to the Zoophycos ichnofacies, the archetypal Cruziana ichnofacies and the Skolithos ichnofacies in wave-dominated shoreface-offshore complex point to stress-free environmental conditions in open waters due to persistent wave agitation, and hence, a wide colonization window.

Responses of molluscan communities to centuries of human impact in the northern Adriatic Sea.

In sediment cores spanning ~500 years of history in the Gulf of Trieste, down-core changes in molluscan community structure are characterized by marked shifts in species and functional composition. Between the 16th and 19th century, a strong heavy metal contamination of the sediments, most notably by Hg, together with the effects of natural climatic oscillations (increased sedimentation and organic enrichment) drive community changes. Since the early 20th century up to 2013, the combined impacts of cultural eutrophication, frequent hypoxic events and intensifying bottom trawling replace heavy metal contamination and climatic factors as the main drivers. The pollution-tolerant and opportunistic bivalve Corbula gibba and the scavenging gastropod Nassarius pygmaeus significantly increase in abundance during the 20th century, while species more sensitive to disturbances and hypoxia such as Turritella communis and Kurtiella bidentata become rare or absent. An infaunal life habit and scavenging emerge as the dominant life strategies during the late 20th century. Down-core shifts in the proportional abundances of molluscan species and functional groups represent a sensitive proxy for past ecological changes and reveal a century-long anthropogenic impact as the main driver behind these processes in the northern Adriatic Sea, offering also a unique perspective for other shallow marine ecosystems worldwide.

Life in the arena: infaunal gastropods and the late Phanerozoic expansion of marine ecosystems into sand

AbstractMarine ecosystems have expanded into the infaunal realm below the surface of soft sediments throughout the Phanerozoic eon. During the Palaeozoic era, this expansion largely involved sedentary animals living in permanent resting places. Active sand‐burrowing animals colonized the infaunal environment later, but when this happened and when specialization for infaunal life evolved remain open questions. Here, phylogenetic evidence, fossil occurrences and previously established criteria for recognizing the sand‐burrowing habit in marine gastropods are used to determine how many gastropod clades became infaunal and when the transitions from surface‐dwelling to infaunal life occurred. At least 20, and as many as 35, clades (all but one of post‐Palaeozoic age) contain actively infaunal species. The overwhelming majority (15 of 20 clades) became infaunal during the Cenozoic, and clades with hundreds of infaunal species in the living fauna diversified beginning in the Early Miocene. The repeated evolution of, and specialization to, the sand‐burrowing habit by gastropods and other animals was enabled by increased habitat availability and higher marine productivity, and was necessitated by intensifying predation. As a result, the infaunal realm was transformed from a marine refuge to an integrated part of the marine biosphere in which high performance in locomotion and defence has become the norm.

Systematics, age, paleoecology and paleobiogeography of Jurassic foraminifera from Fakirwari Dome, Kutch, Gujarat, India

The studied section of the Chari Formation exposed at Fakirwari Dome, Kutch yielded rich foraminiferal assemblages comprising 54 species, ofwhich 22 are reported for the first time from the Indian region. The foraminiferal species are systematically described and employed for interpretations of age, paleoecology, and paleobiogeography. Although most of the foraminiferal species are rather long ranging, on the basis of a few species characteristic of the Callovian in diffrent parts of the world, a Callovian age is assigned to the studied sequence. Based on the dominance of suborder Lagenina, superfamily Nodosariacea, family Vaginulinidiae, calcareous hyaline forms, genus Lenticulina, wide ranging and fluctuating Fisher index, morphogroup K, and potential deep infaunal life habit group in the present assemblages, a shallow water, near shore, open marine middle shelf environment with frequently fluctuating shoreline having normal salinity and nomal to high level of oxygen is envisaged for the studied assemblages. The Middle Jurassic Fakirwari foraminiferal assemblages are assigned to a separate province of the Antiboreal Realm, the Indo-East African Province, located at the southern margin of the Tethyan Realm and transitional between the Tethyan and the Antiboreal realms.

Equatorward increase in naticid gastropod drilling predation on infaunal bivalves from Brazil with paleontological implications

Abstract Understanding the influence of spatial variation on temporal trends is important for interpreting evolutionary patterns of predation in the fossil record. Geographic data on naticid gastropod drilling predation are contradictory and mostly limited to the Northern Hemisphere. This study examines latitudinal variation in drilling on ~ 24,000 beach-collected Recent bivalves from 6°S to 34°S in Brazil. Twenty-eight localities representing 16 latitudes were sampled in the Brazilian and Argentinean provinces, further subdivided into four smaller ecoregions (Northeastern Brazil, Eastern Brazil, Southeastern Brazil, Rio Grande). Analyses focused on bivalves exhibiting infaunal life habits. Increased drilling equatorward was observed at the assemblage-level across several spatial scales (localities, latitudes, ecoregions, provinces). Taxon-level analyses for eight genera drilled across multiple ecoregions generally indicated greater drilling among lower latitudes; size standardization did not affect patterns at the genus level. An equatorward increase in drilling was documented also upon restricting the data to localities characterized primarily by softer substrates, fine- to medium-grained sediments, and in limiting data to samples obtained by a single collecting strategy, minimizing concerns regarding the influence of local environmental variation and different methodologies on latitudinal patterns in drilling. Latitudinal patterns in drilling may be related to temperature and seasonality in influencing metabolic rates, as well as diversity and predator–prey size distributions. The results of this study do not correspond to existing patterns previously described for Western Atlantic molluscan assemblages of the Northern Hemisphere. However, they may help explain temporal patterns in the fossil record of naticid predation.

Persistent ecological shifts in marine molluscan assemblages across the end-Cretaceous mass extinction

Contemporary biodiversity loss and population declines threaten to push the biosphere toward a tipping point with irreversible effects on ecosystem composition and function. As a potential example of a global-scale regime shift in the geological past, we assessed ecological changes across the end-Cretaceous mass extinction based on molluscan assemblages at four well-studied sites. By contrasting preextinction and postextinction rank abundance and numerical abundance in 19 molluscan modes of life--each defined as a unique combination of mobility level, feeding mode, and position relative to the substrate--we find distinct shifts in ecospace utilization, which significantly exceed predictions from null models. The magnitude of change in functional traits relative to normal temporal fluctuations at far-flung sites indicates that molluscan assemblages shifted to differently structured systems and faunal response was global. The strengths of temporal ecological shifts, however, are mostly within the range of preextinction site-to-site variability, demonstrating that local ecological turnover was similar to geographic variation over a broad latitudinal range. In conjunction with varied site-specific temporal patterns of individual modes of life, these spatial and temporal heterogeneities argue against a concerted phase shift of molluscan assemblages from one well-defined regime to another. At a broader ecological level, by contrast, congruent tendencies emerge and suggest deterministic processes. These patterns comprise the well-known increase of deposit-feeding mollusks in postextinction assemblages and increases in predators and predator-resistant modes of life, i.e., those characterized by elevated mobility and infaunal life habits.

Umbonal musculature and relationships of the Late Triassic filibranch unionoid bivalves

Exceptionally well-preserved Late Triassic unionoids from Silesia, Poland, show prominently ornamented juvenile shells and umbonal muscle attachments that are similar to Margaritifera, which are anatomically the least derived among extant unionoids. Their phosphatized (originally chitinous and impregnated with calcium phosphate) gill supports lacked transverse connections, and occasionally some of them were separated from others, being thus at the filibranch grade, like their trigonioid ancestors. Several separate small foot elevator attachments in these unionoids indicate Trigonodidae adaptation to marine or brackish water, in which the original trigonioid strong single attachment was already split into two in the Early Triassic. The ribbing of juvenile shells suggests a change to deeper infaunal life for juvenile stages, and generally less efficient near-surface locomotion, with a wedge-like foot, in adults. Much later the unionoids became eulamellibranchial, which promoted the brooding of the fish that their larvae parasitize. To accomodate the classification of the order under this scenario of evolutionary changes, a new suborder Silesunionina is proposed for its filibranch members. It includes the Silesunionidae fam. nov., with the location of umbonal muscles similar to that in the extant underived unionoids, and the Unionellidae fam. nov., with umbonal muscles attached to the external wall of the umbonal cavity. The early Late Triassic (Carnian) Silesunio parvus gen. et sp. nov. and latest Triassic (Rhaetian) Tihkia(?) silesiaca sp. nov. are proposed. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163, 863–883.

Changes in shell durability of common marine taxa through the Phanerozoic: evidence for biological rather than taphonomic drivers

Phanerozoic trends in shell and life habit traits linked to postmortem durability were evaluated for the most common fossil brachiopod, gastropod, and bivalve genera in order to test for changes in taphonomic bias. Using the Paleobiology Database, we tabulated occurrence frequencies of genera for 48 intervals of ∼11 Myr duration. The most frequently occurring genera, cumulatively representing 40% of occurrences in each time bin, were scored for intrinsic durability on the basis of shell size, reinforcement (ribs, folds, and spines), life habit, and mineralogy.Shell durability is positively correlated with the number of genera in a time bin, but durability traits exhibit different temporal patterns across higher taxa, with notable offsets in the timing of changes in these traits. We find no evidence for temporal decreases in durability that would indicate taphonomic bias at the Phanerozoic scale among commonly occurring genera. Also, all three groups show a remarkable stability in mean shell size through the Phanerozoic, an unlikely pattern if strong size-filtering taphonomic megabiases were affecting the fossil record of shelly faunas. Moreover, small shell sizes are attained in the early Paleozoic in brachiopods and in the latest Paleozoic in gastropods but are steady in bivalves; unreinforced shells are common to all groups across the entire Phanerozoic; organophosphatic and aragonitic shells dominate only the oldest and youngest time bins; and microstructures having high organic content are most common in the oldest time bins.In most cases, the timing of changes in durability-related traits is inconsistent with a late Mesozoic Marine Revolution. The post-Paleozoic increase in mean gastropod reinforcement occurs in the early Triassic, suggesting either an earlier appearance and expansion of durophagous predators or other drivers. Increases in shell durability hypothesized to be the result of increased predation in the late Mesozoic are not evident in the common genera examined here. Infaunal life habit does increase in the late Mesozoic, but it does not become more common than levels already attained during the Paleozoic, and only among bivalves does the elevated late Mesozoic level persist through the Holocene.These temporal patterns suggest control on the occurrence of durability-related traits by individual evolutionary histories rather than taphonomic megabiases. Our findings do not mean taphonomic biases are absent from the fossil record, but rather that their effects apparently have had littleneteffect on the relative occurrence of shell traits generally thought to confer higher preservation potential over long time scales.

Biotic influences on species duration: interactions between traits in marine molluscs

We analyze relationships among a range of ecological and biological traits—geographic range size, body size, life mode, larval type, and feeding type—in order to identify those traits that are associated significantly with species duration in New Zealand Cenozoic marine molluscs, during a time of background extinction. Using log-linear modeling, we find that bivalves have only a small number of simple, two-way associations between the studied traits and duration. In contrast, gastropods display more complex interactions involving three-way associations between traits, a pattern that suggests greater macroecological complexity of gastropods. This is not an artifact caused by the larger number of gastropods than bivalves in our data set. We used stratified randomized resampling of families to test for associations between traits that might result from shared inheritance rather than ecological trait interactions; we found no evidence of phylogenetic effects in any associations examined. The relationships revealed by our study should serve to constrain the range of possible biological mechanisms that underlie these relationships. As previously observed, two-way associations are present between large geographic range and increased duration, and between large geographic range and large body size, in both bivalves and gastropods. In gastropods, planktotrophic larval type is associated with large range size through a three-way interaction that also involves duration; there is no direct association of larval type and geographic range. Gastropods also display two-way associations between duration and life mode, and duration and feeding type. We note that in gastropods, an infaunal life mode is associated with large range size, whereas in bivalves infaunality is associated with reduced range size.

A TEST OF BIOGEOGRAPHICAL, ENVIRONMENTAL, AND ECOLOGICAL EFFECT ON MIDDLE AND LATE TRIASSIC BRACHIOPOD AND BIVALVE ABUNDANCE PATTERNS

Analysis of Middle Triassic data indicates that biogeography influences sample distributions, whereas depositional environment and stratigraphic position play secondary roles in governing sample patterns. During this time, taxa differed among biogeographic realms, while the general ecology remained the same: epifaunal benthos— pedunculate and epibyssate suspension feeders—dominate Middle Triassic samples much as they did in the Early Triassic. In contrast, Late Triassic data prove to be more complex in terms of ecology compared to Middle Triassic. Here, guild structure dictates the faunal patterns in addition to biogeographic realm and stratigraphic position, and an overall increase of infaunal life habits occurs—burrowing suspension and deposit feeders increase. Although diversity after mass extinction began to recover at the Early-Middle Triassic boundary, our results indicate that ecology remained stable through the Middle Triassic until the more modern life habits (e.g., infaunalization) increased in the Late Triassic. We conclude that the taxonomic and ecological differences among Late Triassic geographic regions recorded the initiation of a more mobile and infaunal life habit indicative of a modern lifestyle. Our results also indicate that this modernization did not necessarily unfold simultaneously and in coordinated fashion within regions and throughout time. Instead, details of guild expansion or stability may be region specific.

A re-examination of the Nama-type Vendian organism Rangea schneiderhoehni

The need to re-examine Rangea has been motivated by two factors: first, by the recent progress in the understanding of three-dimensional mouldic preservation of Vendian fossils, and second, by discoveries of this taxon outside Gondwana albeit in the same sedimentary environment as seen in Namibia. Several important features are revealed, including the in situ posture in the sediment, the double-layered quilted structure, the tripartite stemless body and the mucous-supported sheath in the sediment. It is suggested that Rangea represents an infaunal organism, and that the similarity with other members of the Nama-type biota reflects convergence in functional and fabricational constraints in relation to infaunal life habit.

The youngest carpoid: occurrence, affinities, and life mode of a Pennsylvanian (Morrowan) mitrate from Oklahoma

Abundant, well-preserved specimens of a new peltocystidan mitrate carpoid,Jaekelocarpus oklahomensisn. gen. and sp., have been discovered in the Pennsylvanian (Morrowan Series) Gene Autry Shale Member, Golf Course Formation, in southern Oklahoma. The new carpoid postdates the youngest previously known carpoids (Middle Devonian) by about 65 million years. It is characterized by a small (to 4 mm in length) globose theca composed of six plates: two large adaulacophorals, two large marginals, and two relatively small plates that frame the main thecal orifice. One of the plates at the orifice bears a single stout spine. The theca and plates that comprise the theca display a high degree of bilateral symmetry. In contrast, the styloid has an asymmetrical array of spines and blades.We hypothesize that most mitrates, including this one, were adapted to an infaunal life mode. The streamlined, generally symmetrical body shape is an adaptation to moving on or through the substrate. Spines and blades on the lower surface of the styloid and proximal aulacophore are inferred to be adaptations for gripping the substrate as the animal pulled itself backwards (aulacophore first). The main thecal orifice opposite the aulacophore was the site of both mouth and anus. Evidence for a sluggish, epifaunal life mode in the cornute carpoids includes the typically flattened, asymmetrical body, the presence of downward projecting spines and knobs on the marginal thecal plates of many species, and the specialized thecal pores and slits that faced away from the substrate.

The influence of hydrodynamic regime on infaunal assemblages inhabiting carbonate sediments on central Pacific seamounts

We investigated the following hypotheses for deep seamounts in the central Pacific Ocean: (1) infaunal and microbial abundances are elevated in regions of current intensification, (2) infaunal lifestyles reflect variation in hydrodynamic conditions and (3) bioturbation is more intense in high-energy regimes. Our studies were carried out at three sites: the northwest perimeter of the Horizon Guyot sediment cap (1840 m), which is characterized by strong bottom currents and rippled foraminiferan sands, and the central summits of Horizon Guyot (1480 m) and Magellan Rise (3150 m), whose sediments are unrippled and finer grained. Contrary to our first hypothesis, the high-energy, Horizon perimeter sediments exhibited lower biological activity than the summit sites, as reflected in lower organic nitrogen (0.011% vs. 0.015–0.017%), higher C/N ratios (19 vs 11), lower bacterial counts (1.21 vs 2.03−2.15 × 10 8ml −1) and lower macrofaunal abundances (255 vs 388–829 m −2). Sediment organic carbon values (0.14–0.19%) and meiofaunal abundances (2866–5150 m −2) did not differ significantly among the three sites. Infaunal life habits varied among sites but sediment mixing did not. Macrofauna were found deeper in rippled perimeter sediments than in the cap sediments. Sessility and surface-feeding modes dominated among polychaetes at the higher-energy Horizon perimeter, while motility and subsurface feeding were common in the quieter, finer-grained regimes. Significant sediment mixing takes place on 100-year time scales a all three sites, probably a result of large, infaunal bioturbators at the cap sites and physical sediment instability at the perimeter site. Excess 210Pb exhibited moderately high inventories (38–59 dpm cm −2) and deep penetration (15 cm). Estimated mixing coefficients (D b) ranged from 0.6 to 3.0 cm 2y −1 at the three sites. Our findings indicate that hydrodynamic differences can lead to greater variation in sediment and faunal characteristics on a single seamount than are found in similar regimes on different seamounts. Comparison of the Horizon Guyot and Magellan Rise data to comparable data from eastern Pacific seamounts, reveals lower organic carbon content, microbial abundance, macrofaunal densities, and subsurface deposit feeder representation, in central than eastern Pacific seamount sediments.