Firm Substrates Research Articles

Seaweed-like Co-MOF/Cu(OH)2/CF composite as an advanced pre-catalyst for oxygen evolution reaction

Directly applying metal-organic frameworks (MOFs) as electrocatalysts or pre-catalysts for the oxygen evolution reaction (OER) faces significant challenges, due to the lack of exposed active sites, low electronic conductivity, and poor structure stability. Herein, a novel alkaline leaching-solvothermal strategy is proposed to synthesize seaweed-like Co-MOF/Cu(OH)2 on copper foam (CF), which is applied as self-supporting pre-catalyst for OER. After electrochemical activation, Co-MOF/Cu(OH)2/CF only requires an overpotential of 279 mV at 50 mA cm-2 and operates steadily for 72 h with negligible activity deterioration. The high activity and stability mainly benefit from the unique structural arrangement, in which Cu(OH)2 nanoneedles serve as firm substrates to grow and stabilize Co-MOFs. The two-dimensional Co-MOFs with nanometer thickness and high accessible surfaces could expose sufficient metal coordination sites, which are ready for reconstruction and electrocatalysis. Additionally, CF framework helps to maintain the self-supporting structure and acts as current collector to enhance the charge/electron transfer efficiency during OER.

Macroalgae from the early Cambrian Chengjiang biota

AbstractThe Chengjiang biota, a Burgess Shale‐type Lagerstätte in eastern Yunnan, South China (Cambrian Series 2, Stage 3), provides valuable information regarding the origin and early evolution of metazoans, and complex marine ecosystems. Although the major animal phyla in the Chengjiang biota have been extensively studied, macroalgae have received comparatively little attention. Here, we establish new taxa Yunnanospirellus typica and Y. elegans, describe five genera and six species (Tawuia sp., Morania fragmenta, Liulingjitaenia alloplecta, Longfengshania stipitata, Lo. spheria and Paralongfengshania sicyoides) not previously reported in the Chengjiang biota, and elucidate the pith structure of Enteromophites intestinalis. With 13 genera and 17 species now recorded, macroalgae rank fourth in species‐level biodiversity in the Chengjiang biota (behind Euarthropoda, Porifera and Priapulida). Macroalgae account for 71.57% of total abundance, far more than all other animal phyla in the Chengjiang biota. Fuxianospira is the most dominant genus, accounting for 52.01% of all macroalgae specimens. Unattached (floating, planktonic or drifting) forms dominate (eight attached; nine unattached species). The high diversity of attached macroalgae indicates that the macroalgal communities adapted to the Proterozoic firm substrate (probably covered by microbial mats) persisted from the Ediacaran to the early Cambrian, providing compelling evidence for the existence of firm substrate during this time. Meanwhile, the blooming of unattached macroalgae in the Chengjiang biota suggests that other niches were also rich in macroalgae. Unattached macroalgae might have provided oxygen and energy to metazoans, eventually leading to ecological expansion in the upper and middle water column of the early Cambrian seas.

Ichnology of tidal ravinement omission surfaces in siliciclastic transgressive deposits from the Puesto El Moro formation (Upper Cretaceous), Southern Patagonia, Argentina

Omission surfaces represent a gap in the sedimentary record on a particular environment, constituting an important tool for basin analyses. Nevertheless, not always these surfaces constitute key sequence-stratigraphic surfaces, and their correct interpretation is highly important for the recognition of genetically related strata. Documentation and interpretation of ichnological data from stratigraphic surface can refine the sedimentological model. The Puesto El Moro Formation (lower Upper Cretaceous) in the Austral-Magallanes Basin, southern Patagonia (Argentina), shows excellent examples of several omission surfaces stacked during a transgressive context associated with the beginning of the foreland stage. Each of these surfaces, interpreted as Tidal Ravinement Surfaces, contain Thalassinoides isp. and Sinusichnus isp., which represent opportunistic colonization by crustaceans into a predominantly firm substrate. In this case study, the vertical recurrence of substrate-controlled trace fossil suites is the result of high-frequency repeated coastal conditions during the transgression; the associated surfaces, which have limited lateral extension, have low potential for correlation at basin scale.

Ecomorphology of the cervid intermediate phalanx and its implications for palaeoenvironmental reconstruction.

This paper reports on newly developed ecomorphological models for the cervid intermediate phalanx. Using a geometric morphometric approach, we quantitatively assess the overall gracility of the bone, the depth and concavity of the proximal articulation and the roundness and symmetry of the distal articulation in the intermediate phalanx, to establish relationships between morphology, locomotor behavior and environment. The morphology of the phalanx was found to vary along a gradient from gracile phalanges with shallow proximal articulations in forms adapted to yielding substrate, to robust phalanges with deeper proximal articulations in taxa adapted to firm substrate. Phylogeny and allometry are accounted for using regressions and phylogenetic comparative methods. Although the results indicate phylogeny explains part of the morphological variation, overall the shape of the intermediate phalanx appears mainly driven by differences in function. Consequently, this element promises to be a useful palaeoenvironmental proxy that can be applied on fossil assemblages with cervid remains.

Evolution of Holdfast Diversity and Attachment Strategies of Ediacaran Benthic Macroalgae

Holdfast morphologies and attachment strategies of benthic macroalgae are somewhat flexible and controlled by both the substrate condition and species. Six forms (tapered base, globose holdfast, composite globose holdfast, discoidal holdfast, rhizoids and horizontal rhizomes) of attachment structures of Ediacaran benthic macroalgae are recognized from the early Ediacaran Lantian biota and late Ediacaran Miaohe biota in South China based on functional morphology. Each form is considered either adapted to firm substrates that dominate the Precambrian seafloor, or soft substrates that are more common in the Phanerozoic. The results show a diversification in both holdfast morphology and attachment strategies of macroalgae during the Ediacaran Period. In the early Ediacaran Lantian biota, none of the benthic macroalgae is adapted to soft substrates, while in the late Ediacaran Miaohe biota, a considerable number (41%) of species are adapted to relatively soft substrates. This shift might be an adaptive response to the diversification of macroalgae and a changing substrate condition during the Ediacaran Period: the decline of microbial mats and increase of water content in the sediments in the Ediacaran.

High-Performance Flexible InAs Thin-Film Photodetector Arrays with Heteroepitaxial Growth Using an Abruptly Graded InxAl1-xAs Buffer.

Current infrared thermal image sensors are mainly based on planar firm substrates, but the rigid form factor appears to restrain the versatility of their applications. For wearable health monitoring and implanted biomedical sensing, transfer of active device layers onto a flexible substrate is required while controlling the high-quality crystalline interface. Here, we demonstrate high-detectivity flexible InAs thin-film mid-infrared photodetector arrays through high-yield wafer bonding and a heteroepitaxial lift-off process. An abruptly graded InxAl1-xAs (0.5 < x < 1) buffer was found to drastically improve the lift-off interface morphology and reduce the threading dislocation density twice, compared to the conventional linear grading method. Also, our flexible InAs photodetectors showed excellent optical performance with high mechanical robustness, a peak room-temperature specific detectivity of 1.21 × 109 cm-Hz1/2/W at 3.4 μm, and excellent device reliability. This flexible InAs photodetector enabled by the heteroepitaxial lift-off method shows promise for next-generation thermal image sensors.

Disaster microconchids from the uppermost Permian and Lower Triassic lacustrine strata of the Cis-Urals and the Tunguska and Kuznetsk basins (Russia)

AbstractWe describe aggregative microconchid (Lophophorata) tubes from the uppermost Permian (upper Changhsingian) and Lower Triassic (Olenekian) lacustrine and fluvial strata of the Tunguska and Kuznetsk basins and the southern Cis-Urals, Russia. These attach to clam shrimp carapaces, bivalve shells, terrestrial plant fragments and a horseshoe crab head shield, and also form their own monospecific agglomerations. Planispiral tubes of a wide size range (0.1–2.5 mm) create dense settlements on these firm substrates, which likely comprise multiple generations of the same species. These finds confirm that this extinct lophophorate group was inhabiting non-marine continental basins during latest Permian and earliest Triassic time, when they were major suspension feeders in such limnic ecosystems. Microconchids dispersed extensively and rapidly in the aftermath of the Permian–Triassic mass extinction into both marine and continental basins at low and moderately high latitudes, which were notably different in salinity, temperature, depth and redox conditions. This confirms that small lightly calcified microconchids were a genuine disaster eurytopic group, whose expansion may have been promoted by low predator pressure and low competition for substrate.

In situ filamentous communities from the Ediacaran (approx. 563 Ma) of Brazil.

Precambrian filamentous microfossils are common and diverse. Nevertheless, their taxonomic assignment can be difficult owing to their overall simple shapes typically lacking in diagnostic features. Here, we report in situ communities of well-preserved, large filamentous impressions from the Ediacaran Itajaí Basin (ca 563 Ma) of Brazil. The filaments are uniserial (unbranched) and can reach up to 200 µm in width and up to 44 mm in length. They occur as both densely packed or sparsely populated surfaces, and typically show a consistent orientation. Although simple in shape, their preferred orientation suggests they were tethered to the seafloor, and their overall flexibility (e.g. bent, folded and twisted) supports a biological (rather than sedimentary) affinity. Biometric comparisons with modern filamentous groups further support their biological affinity, suggesting links with either large sulfide-oxidizing bacteria (SOB) or eukaryotes. Other morphological and palaeoecological characteristics further corroborates their similarities with modern large filamentous SOB. Their widespread occurrence and association with complex Ediacaran macrobiota (e.g. frondose organisms, Palaeopascichnus) suggest that they probably played an important role in the ecological dynamics of these early benthic communities by providing firm substrates for metazoans to inhabit. It is further hypothesized that the dynamic redox condition in the latest Ediacaran, with the non-continuous rise in oxygen concentration and periods of hypoxia, may have created ideal conditions for SOB to thrive.

Nanosheets based mixed structure CuCo2O4 hydrothermally grown on Ni foam applied as binder-free supercapacitor electrodes

• Nanosheets mixed structure CuCo 2 O 4 on Ni foam was synthesized by a facile hydrothermal reaction. • Nanosheets mixed structure CuCo 2 O 4 show the superior electrochemical performances. • CuCo 2 O 4 nanosheets exhibit specific capacitance of 1595 F g −1 at 1 A g −1 and good cycling stability. CuCo 2 O 4 has been successfully hydrothermally grown on Ni foam. The morphology of the sample are observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The product has a unique morphology based on nanosheets which can self-assembly into two main structure. The electrode exhibits good electrochemical performance in supercapacitor application. The specific capacitance is 1595 F g −1 at 1 A g −1 , and specific capacitance keeps 85.1% after 4600 cycles. Such performance may be responsible for some factors. Three-dimensional Ni foam can be regarded as a conductive skeleton and firm substrate. It can further enhance the conductivity by not using binders. The unique mixed structure can provide more exchange between electrode and electrolyte. Both faster electron transmission and shorter ion diffusion path facilitate the redox reactions which can improve the electrochemical performance. The results indicate the nanosheet based mixed structure CuCo 2 O 4 grown on Ni foam have a promising future as supercapacitor electrodes. CuCo 2 O 4 nanosheets grown on Ni foam applied as binder-free electrode of supercapacitor shows an impressive enhancement of the performance including the areal capacitance and cycling stability.

Potential effects of biodegradable single-use items in the sea: Polylactic acid (PLA) and solitary ascidians

With conventional plastics posing a great threat to marine organisms, and potentially also to humans, bio-based, biodegradable plastics are being offered as an ecological solution by which to reduce the environmental impact. Inside compost facilities, bioplastics that comply with the EN 13432:2000 international standard biodegrade almost completely within 180 days. However, outside compost facilities, and specifically in marine environments, these bioplastics may have a similar effect to that of fossil-fuel based plastics. Here we investigated the effects of polyethylene terephthalate (PET) and polylactic acid (PLA) single-use cups and plates on a solitary ascidian’s biological and ecological features. Both PET and PLA microparticles reduced the fertilization rate of Microcosmus exasperatus, with no significant difference between materials. Accumulation rates in adult M. exasperatus exposed to micronized PET and PLA particles at two concentrations were similar for both the bioplastic material and the conventional plastic particles, with no significant difference between the two materials. A microbial-based digestive protocol was developed in order to recover the bioplastic material from ascidian tissue and reduce any material-loss caused by the known digestion protocols. Finally, PET plates submerged for three months in the Red Sea exhibited a significantly higher community richness and cover area in comparison to PLA plates, which did not provide a firm substrate for settlers. Indeed, coverage by the solitary ascidian Herdmania momus was significantly higher on PET plates. The current study demonstrates that discarded bioplastic products may have similar effects to those of conventional plastics on marine organism fertilization and biological accumulation, emphasizing the need to revise both the production and marketing of “biodegradable” and “compostable” plastics in order to prevent a further negative impact on ecosystems due to the mismanagement of bioplastic products.

Firmground crustacean burrow systems (Glossifungites ichnofacies) in marine shelf deposits, Paleocene Clayton Formation, Alabama, USA

The Paleocene (Danian) Clayton Formation of western Alabama, USA, includes multiple marine shelf parasequences, each comprising a relatively thick marl, capped by a thin limestone, the latter variably reflecting marine flooding episodes. The marls host relatively large firmground burrow systems that penetrate 50–60 cm beneath, and are cast by, superjacent limestones. Excavation of two partially exposed burrow systems – one beneath a highstand parasequence-bounding flooding surface and the other beneath an overlying coplanar sequence boundary/transgressive surface (SB/TS) – reveals complex, primarily horizontal, irregularly branching networks. The former, allied with Thalassinoides paradoxicus, lacks wall bioglyphs, whereas the latter, allied with Spongeliomorpha iberica, is characterized by pervasive, mainly rhombohedral wall bioglyphs that reflect a relatively more firm substrate. Contrasts between these burrow systems are consistent with sequence stratigraphical context and inferred differences in the mechanism and magnitude of depositional hiatuses responsible for firmground development. Both excavated burrow systems likely represent cumulative structures produced by multiple organisms over extended periods of time. The cumulative nature and potential taphonomic biases associated with these and comparable burrow systems in the stratigraphical record preclude confident interpretation of tracemakers and their behaviours. The Clayton burrow systems likely were produced by one or more species of decapod crustacean that engaged in suspension-feeding, surface detritus feeding, gardening or some combination thereof.

Taking advantage of seagrass recovery potential to develop novel and effective meadow rehabilitation methods.

Seagrasses are among the most threatened biomes worldwide. Until now, seagrass rehabilitation success has reached about 38% overall and more effective approaches to restoration are urgently needed. Here we report a novel method to rehabilitate Posidonia oceanica meadows based on observation of the species' natural recovery after disturbance. Posidonia oceanica rhizomes were transplanted on gabions filled with rocks of selected sizes in order to build a firm substrate with topographic complexity in the relevant scale range to propagules. Five techniques were tested, each involving a different anchoring device. The "slot" technique, which uses a wire-net pocket to retain the cuttings, was the most successful, with survival exceeding 85% after thirty months. Branching allowed final shoot survival to reach 422% of initial planting density. This study shows how an in-depth knowledge of species life history processes provides a suitable foundation for developing effective restoration methods that benefit from species recovery ability.

Firm evidence for a post-extinction ichnofauna: earliest CarboniferousCruziana reticulataassemblage from the Anti-Atlas of Morocco

Cruziana reticulata is an arthropod-related ichnospecies that is characterized by a conspicuous net-like scratch pattern whose initial formation and later preservation require the presence of consolidated substrates in shallow marine fine-grained bottoms. There are two scenarios in which epifaunal to shallow infaunal benthic organisms may access firm siliciclastic substrates: first, by exposure of the compacted bottom after erosion of the upper, water-saturated and usually soft portion of sediment column; and, second, by primary fast substrate stabilization in the absence of biogenic sediment mixing. Whereas the first mode occurs throughout the Phanerozoic, the latter is only prevalent in marine bottoms during the Early Palaeozoic mainly as a consequence of poorly developed infaunal bioturbation. However, by eradicating burrowing organisms, mass extinctions are known (i.e. the end-Permian extinction) to ‘reset’ intensity of ecospace utilization, which entails the return to this anachronistic style of trace fossil preservation in younger times. An earliest Carboniferous ichno-assemblage dominated by Cruziana reticulata from Morocco attests the spread of firm substrates in the aftermath of the Hangenberg Event – a major extinction at the end of the Devonian period. Since evidence for erosion is lacking in accompanying sedimentary rocks and the ichno-assemblage shows characteristics of opportunistic exploitation of the nutritious muddy seabed, we favour the interpretation of this assemblage to represent a post-extinction ichnofauna. It shows that other taxonomically less severe mass extinctions may also exhibit transient but severe ecological effects in open marine ecosystems such as the collapse of vital sediment mixing. Such post-extinction effects may distort the perception of the stratigraphical record as a firmground ichno-assemblage often taken as evidence for submarine erosion and are crucial in highlighting sequence boundaries. We, thus, encourage appreciating macroevolutionary framework of respective ichnofaunas.

Gigantoproductid and allied productid brachiopods from the “Calcaires à Productus” (late Viséan-Serpukhovian; Montagne Noire, southern France): Taxonomy and palaeobiogeographical position in the Palaeotethys

The “Calcaires à Productus” or “Calcaires à Productus giganteus” on the southern slope of the Montagne Noire (Hérault, France) consist of numerous isolated olistolitic limestone blocks, generally transported by gravitational flows into siliciclastic basinal deposits. The present paper is the first systematic monographic study of gigantoproductids, semiplanids, and some other large-sized productid brachiopods from the upper Viséan to Serpukhovian strata of the Montagne Noire. Gigantoproductids are represented by abundant Datangiasemiglobosa and Kansuella spp.; a single Globosoproductus specimen is described. The semiplanids are represented by Latiproductus aff. latissimus, L. latissimus complicatus and L. edelburgensis, and the linoproductids by Balakhonia aff. kokdscharensis. The Montagne Noire productid faunas are found in very different facies including shell beds and microbial mounds. They are most abundant in assemblages from agitated, shallow water environments with a firm substrate where rugose corals are rare or absent. The palaeobiogeographical relations to the other regions in the western Palaeotethys are often limited to taxa with an almost cosmopolitan character. Worth noting is the absence of Gigantoproductussensu stricto in the Montagne Noire. This genus, and other brachiopod taxa, migrated probably during the late Serpukhovian into southern France. On a larger scale, the presence of Kansuella indicates faunal exchanges with the eastern Palaeotethys (South China) via a westward migration path along North China, the Central Asian Orogenic Belt and south-eastern Laurussia. The studied taxa, even at the genus level, did not migrate into North America even if the Alleghanian Isthmus was still open.

Sulcolithos variabilis igen. et isp. nov.: grooves on firm and hard bedding surfaces

The trace fossil Sulcolithos variabilis igen. et isp. nov. is described from the Middle Triassic (Ladinian) Muschelkalk Group of Germany. The groove-like structures occur on the surface of limestone beds that provided firm to hard substrate to the burrowing and/or boring organisms. The grooves have an elongate, straight or curved course and can be compound with subsurface burrow systems of Balanoglossites. Similar trace fossils have been reported from Late Ediacaran to Holocene deposits, and seem to be prevalent in Ordovician, Triassic and Jurassic time. Based on indirect evidence (e.g. morphology, interrelationship with Balanoglossites, substrate property), S. variabilis is attributed to the combined burrowing and boring activity of polychaetes. This interpretation is supported by direct evidence, such as the occurrence of exceptionally preserved polychaete remains in the traces, both in the Triassic material from Germany and the Ordovician specimens from Anticosti Island, Canada. However, morphologically similar traces in soft and firm substrate can also be produced by other organisms (e.g. bivalves) and represent behavioural convergence.

Evolution of Eye Reduction and Loss in Trilobites and Some Related Fossil Arthropods

The fossil record of arthropod compound eyes reflects different modes and occasions of eye reduction and blindness. In the best-studied fossil examples, the trilobites [trilobites: extinct arthropods, dominant during the Palaeozoic], which have an excellent geological record, eyes are primary structures, and in all known genera which lack them, eye-loss is always secondary. Once the eyes were lost, they never were never re-established. The most striking examples occur in the Upper Devonian, when two unrelated major groups of trilobites, with different kinds of eyes, underwent eye reduction and even total loss of the eyes over the same time period, undoubtedly due to long-term environmental change. One reason is that a mud blanket spread over a vast area, there was no firm substrate, and many trilobites became small and many became endobenthic, reducing or losing their eyes in the process. Toxic environmental conditions may also have had an effect. Certain coeval forms remained, however, which still possess perfectly good compound eyes. Either they found vacant refuges where they could survive, or alternatively their visual systems were elaborate enough to adapt to the changing conditions. Another inducement for evolving small, reduced compound eyes is to become a tiny organism oneself, with simply not enough space to establish a regular and functional compound eye, and in such minaturised eyes special adaptations for capturing enough photons are necessary. Thus very small compound eyes often establish wide acceptance angles of their ommatidia, collecting light over large angular ranges of space and it is beneficial to have a wide rhabdom provided that it is short, has a wide lens diameter, and perhaps even possess highly sensitive receptor cells. We find such a miniaturised system in the first recorded planktonic trilobite. Another kind of reduction of a compound eye, or parts of it, also occurs, if selective pressure claims for a high specialisation of eyes that results in several facets fusing into a single functional unit. This probably can be found in phacopid trilobites, ~400 million years old. Here the enlarged aperture of a resulting large lens may allow vision under dim light conditions such as at greater depth. The fossil record gives relatively little evidence about parasites, which often have reduced eyes. Agnostida are blind relatives of trilobites which lived during the Cambrian and Ordovician. An early suggestion was that some of these were parasitic, but this was never commonly adopted. Finally penstastomids (Crustacea), worm-like parasitic organisms, already have been blind from the Cambrian (~487Ma).

Altaethyrella(Brachiopoda) from the Late Ordovician of the Tarim Basin, Northwest China, and its significance

AbstractAltaethyrella tarimensis, a new species of rhynchonellide brachiopod, is described from the late Katian (Late Ordovician) Hadabulaktag Formation in the Kuruktag region of Xinjiang, Northwest China on the northeastern edge of the Tarim Basin. Serial sections of the shell clearly show no dorsal median septum or septalium in the dorsal valve, and no spiralia or atrypide-style crura. Like other species of the genus,A.tarimensisn. sp. exhibits a high degree of intraspecific variation, including variations in shell shape and size, number of ribs in the sulcus at the anterior, and degree of asymmetry. The discovery ofAltaethyrellain Tarim has important paleogeographic implications, indicating a close relationship between the Late Ordovician brachiopod faunas of Tarim and those of the Kazakh terranes and North and South China paleoplates, supporting a recently published paleogeographic projection that places Tarim near the Chu-Ili terrane during the Late Ordovician. The abundant large biconvex shells ofA.tarimensisn. sp. would have provided a firm substrate for encrusting filter feeders like bryozoans to establish on the Kuruktag Platform.UUID:http://zoobank.org/df8843cd-4db0-48e7-ba03-bf0ce81c4f01

LIDAR-based characterization and conservation of the first theropod dinosaur trackways from Arkansas, USA.

LIDAR-based analyses of the first theropod dinosaur trackways known from the state of Arkansas, USA are reported. The trackways were found on a limestone bedding plane in the Albian De Queen Formation in an active gypsum quarry. Because limited access precluded thorough field study, fieldwork focused on preserving the entire site digitally with ground-based LIDAR, and detailed measurements were later taken digitally from point cloud data. The site contains eight tridactyl trackways associated with sauropod trackways and numerous isolated tracks. Although there appear to be two different tridactyl morphotypes, we show that the tracks are all likely from a single species of trackmaker. We apply a simple method of estimating substrate consistency by comparing the differences between true track dimensions and apparent track dimensions. The tridactyl tracks at the southern end of the site are preserved with significantly greater differences in true vs. apparent dimensions and are shallower than the rest of the tridactyl tracks at the site, which we interpret as the result of outward expansion of the soft tissues of the foot upon contact with a firm substrate. We interpret the firm substrate as having high bulk density and high shear strength, which also explain associated manus-only sauropod tracks. We show that the tridactyl tracks are likely from theropod trackmakers and that footprint lengths, trackway paces, stride lengths, and pace angulations of the De Queen trackways are statistically indistinguishable from equivalent measurements of theropod trackways in the Glen Rose Formation. The Glen Rose tracks are attributed to the large-bodied theropod, Acrocanthosaurus and we likewise attribute the De Queen tracks to Acrocanthosaurus, which is known from skeletal remains in temporally equivalent units and from the mine itself.

Malongitubus: a possible pterobranch hemichordate from the early Cambrian of South China

AbstractMalongitubus kuangshanensis Hu, 2005 from the early Cambrian Chengjiang Lagerstätte of China is redescribed as a pterobranch and provides the best evidence to demonstrate that hemichordates were present as early as Cambrian Stage 3. Interpretation of this taxon as a hemichordate is based on the morphology of the branched colony and the presence of resistant inner threads consistent with the remains of an internal stolon system. The presence of fusellar rings in the colonial tubes cannot be unambiguously proven for Malongitubus, probably due to early decay and later diagenetic replacement of the thin organic material of the tubarium, although weak annulations are still discernible in parts of the tubes. The description of M. kuangshanensis is revised according to new observations of previously reported specimens and recently collected additional new material. Malongitubus appears similar in most features to Dalyia racemata Walcott, 1919 from the Cambrian Stage 5 Burgess Shale, but can be distinguished by the existence of disc-like thickenings at the bases of tubarium branching points in the latter species. Both species occur in rare mass-occurrence layers with preserved fragmentary individuals of different decay stages, with stolon remains preserved as the most durable structures. Benthic pterobranchs may have occurred in some early Cambrian shallow marine communities in dense accumulations and provided firm substrates and shelter for other benthic metazoans as secondary tierers.

Food and micro-habitat partitioning among cyprinids in Sri Lankan hill-stream pools

Cyprinid fish assemblages in three stream pools in southwest Sri Lanka, were investigated with the objective of analysing species segregation, niche complementarity and degree of resource partitioning. Feeding ecology was studied by gut contents analysis and by direct underwater observations. Dietary data were related to the micro-distribution of the fish and to their horizontal distribution, the latter taken from previously published literature. Diet overlaps were calculated for each pool community and for the community as a whole. Resource partitioning among assemblage members was by diet, micro-distribution and horizontal macro-distribution. Among the three feeding substrates (rocky substrates, sand, dead leaves) rocky substrate was the most preferred, but other substrates, especially dead leaves, were used as well. Only Rasbora daniconius, which mainly fed high in the water column, fed always on rocky substrates at the relative rare occasions that it chose a firm substrate. Pethia nigrofasciata was the only species with a clear preference for sand. The assemblage could be divided into three guilds: (1) the surface feeders (Devario malabaricus, Rasbora daniconius) fed largely on terrestrial arthropods, (2) one generalist Systomus pleurotaenia which fed on all five strata, largely on terrestrial arthropods, ephemeropteran and chironomid larvae. (3) the bottom feeders (Dawkinsia singhala, Pethia cumingii, Pethia nigrofasciata, Puntius dorsalis) who fed preponderantly on chironomid larvae. Of the three niche dimensions, horizontal macro-distribution, micro-distribution and diet, horizontal distribution may be the strongest segregating factor among these fish species. The contribution of diet was substantial only between feeding guilds. A relatively high degree of endemism (ca. 40 % is endemic to Sri Lanka) and habitat partitioning suggests that the cyprinid assemblages studied are predictable, co-evolved systems with competition serving as an importing structuring factor.