In the mud-dwelling amphipod, Corophium volutator the foregut is lined with cuticle and consists of an oesophagus and a stomach, with the latter divided into cardiac, pyloric and funnel regions. The midgut comprises an intestine that is enlarged considerably by three pairs of diverticula: the small anterior dorsal and posterior caeca and the massive ventral caeca. Anteriorly, the intestine encompasses the funnel region and the ventral caeca open into the floor of the stomach at the posterior end of the pyloric region. The hindgut is essentially a simple tube connnecting the intestine with the anus. Particles of food pass along the oesophagus and enter the stomach through a valve. Rows of setae, or folds of cuticle, divide the stomach longitudinally into food, circulation and filtration channels. Ingested particles with a diameter greater than 2 pm are confined to the food channel and supplied with fluids and enzymes from the circulation channels. The digestive enzymes are produced primarily by the ventral caeca and are supplied to the circulation channels through a valve at the entrance of each ventral caecum. Any fine particles and soluble materials extracted from the food channel in the cardiac region are transported into the filtration channels through the first filter of a two part system. Digestible material continues to be extracted in the pyloric region where the volume of the lumen of the food channel is reduced by the intrusion of the vertex of the ventral pyloric ridge. The basis of this ridge supports the second filter which produces a filtrate with particles less than 0.06 pm in diameter. Material retained on the filter membrane is returned to the food channel by brush-like setae facing the membrane. The final filtrate is transported to the ventral caeca. A valve at the entrance to each ventral caecum prevents contamination of the filtrate by material in the food channel. All indigestible food is passed sequentially along the funnel, intestine and, finally, the hindgut from which it is voided as a faecal pellet. Most digestion and absorption occur in the ventral caeca where the epithelium is differentiated into the R /F and B cells. The R /F cells have a much thicker and denser microvillous border than the B cells. Each R /F cell also has numerous mitochondria located mainly ventral to the nucleus in the mid-region. Rough and smooth endoplasmic reticula are sited primarily in the apical and basal regions of the cell, respectively. Furthermore, most of the rough endoplasmic reticulum is confined to cells in the distal region of the caecum which probably forms the main site for the production of digestive enzymes. The proximal region of the caecum contains numerous lipid droplets and is probably involved in the absorption, transport and storage of the products of digestion. Each B cell has a single large, fluid-filled vacuole, distal to which are mitochondria and numerous smaller vacuoles of varying size forming an ‘apical complex’. The nucleus is located proximal to the vacuole together with free ribosomes and rough endoplasmic reticulum. Material from the lumen of the caecum is taken by pinocy tosis into the ‘apical complex’. The large vacuole develops at the expense of the ‘apical complex’ and the microvillous border. The vacuole is eventually liberated into the lumen of the caecum and the cell disintegrates. These discharges may supply enzymes to other regions of the gut, or they could be waste products derived from intracellular digestion. The anterior dorsal caeca and most of the intestine contain cells with a normal complement of organelles. These cells probably make a minor contribution to the processes of digestion and absorption. However, the cells of the posterior caeca and those at the posterior end of the intestine have an extensive development of smooth endoplasmic reticulum. In some cells the mitochondria have a dense matrix and there are only a few free ribosomes and cisternae of rough endoplasmic reticulum. The fine structure of the epithelium in the posterior caeca is typical of tissue that transports fluids and ions. The hindgut has a microvillous border which abuts its cuticular lining. In addition, some cells have numerous mitochondria which are often associated with infolds of the basal cell membrane. The fine structure of this tissue is similar to the ‘ion pumps’ described in the gut of insects which serve to maintain the normal ionic concentration of the blood. The posterior region of the hindgut has no structural specializations.
The isotopic composition of sulfur in convergent margin-related orthomagmatic sulfides is critical to the debate on: 1) petrological mechanisms of sulfide saturation in relatively oxidized magmatic systems, and 2) the relative contribution of subducted sulfate to the overall sulfur budget of the sub-arc mantle. Magmatic sulfides that crystallize in deep-seated plutonic rocks are less susceptible to isotopic fractionation arising from magmatic degassing and are thus better suited for studies of primary S-isotope compositions of arc magmas than their extensively degassed volcanic counterparts. Isotopic compositions of chalcopyrite and pyrrhotite, which crystallized from trapped immiscible sulfide melt, and secondary fibrous pyrite after pyrrhotite in the Polaris Alaskan-type ultramafic-mafic intrusion (Early Jurassic) of the North American Cordillera were determined by secondary ion mass spectrometry. Chalcopyrite grains from five olivine clinopyroxenites are fresh and homogeneous and they have uniform near-chondritic δ34S values (-0.19 +0.48/-0.32‰; n = 97). In contrast, pyrrhotite (δ34S = -1.6 +2.8/-0.6; n = 34) and secondary pyrite (δ34S = -2.7 +1.8/-4.4‰; n = 21) grains display subchondritic but highly variable δ34S. The marked difference in measured δ34S of different sulfide phases attests to the critical advantage of using in-situ microanalytical techniques over whole-rock isotopic analysis. Pyrite grains from hornfelsed volcanogenic country rocks have elevated S-isotope values (δ34S = +7.4 +1.3/-1.7‰; n = 11). The near- to subchondritic isotopic compositions of sulfides from the Polaris intrusion demonstrate that wall-rock assimilation played a minor role and that sulfur in the Polaris magmas is largely magmatic. Fibrous textures and variable, but negative, δ34S of pyrrhotite and pyrite indicate post-magmatic mobility of sulfur due to low-temperature alteration by hydrothermal fluids. The narrow range of chalcopyrite δ34S, however, indicates that it remained unaffected by hydrothermal processes and equilibrated under uniform magmatic physicochemical conditions. Assuming sulfide liquid immiscibility at T ≥ 800 °C, geochemical modeling of S-isotope fractionation indicates that the Polaris parental magmas had suprachondritic δ34S between +1‰ (at log fO2 = FMQ+1) and +5‰ (at log fO2 =FMQ+2), consistent with the contribution of subducted sulfate to the sub-arc mantle.
The general morphology of the antennary and maxillary glands, which form the major renal system of adult Crustacea, has been described and reviewed by Goodrich (1945). However, studies on the fine structure are restricted mainly to the antennary glands of decapods, including Orcotiectes sp. (formerly Cambarus sp.) (Anderson & Beams, 1956; Beams, Anderson & Press, 1956), Orconectes affinis (Kümmel, 1964), Procambarus clarkii (Miyawaki & Ukeshima, 1967; Schaffner & Rodewald, 1978), Procambarus blandingi (Peterson & Loizzi, 1974), Austropotomobius pallipes pallipes (Riegel & Cook, 1975) and Uca mordax (Schmidt-Nielsen, Gertz & Davis, 1968). The maxillary gland of Artemia salina is the only excretory system of a non-decapod which has been studied in detail (Tyson, 1968, 1969 a , b ). Morelli & Tobolla worked independently on the antennary glands of amphipods, Gammarus sp. (cited Kümmel, 1973), but their studies were restricted to the site of filtration.
Abstract Amplification of diagnostic genomic DNA sequences using the highly sensitive polymerase chain reaction (PCR) technique provides a fast, sensitive and relatively inexpensive approach to species identification where there is a lack of diagnostic morphological characters. This applies particularly to the early life-history stages of marine invertebrates. Using PCR primers designed to amplify diagnostic length variants within phylogenetically widespread genes (in this case an expansion segment within the 28S rRNA gene), a first attempt is presented to produce a DNA database for use in the identification of hydrothermal vent larvae. In addition, a scanning electron microscopy study of particulates recovered from the neutrally buoyant plumes of hydrothermal vents on the Mid-Atlantic Ridge revealed evidence of biological material derived both from the vent environment and from the sea surface as marine ‘snow’. This investigation represents the first stage in the development of a bottom-mounted recorder to study the spatial and temporal aspects of larval dispersal in the hydrothermal vent environment. Larval dispersal processes are fundamental to the biogeography, genetics and evolution of the hydrothermal vent fauna.
The Early Jurassic Polaris intrusion in the Canadian Cordillera is an Alaskan-type mafic-ultramafic sill, whose lithological zonation reflects the combined effects of magma differentiation and crystal accumulation, punctuated by recharge and cumulate remobilization. The intrusion contains magmatic mineralization with petrologic and potential economic significance that records the evolution of an oxidized, H2O-rich ultramafic magma. Dunite-hosted platinum group element (PGE) mineralization with high IPGE/PPGE is hosted by thin layers and schlieren of chromitite. Discrete grains of platinum group minerals (laurite) are rare and the bulk of the PGE appear to be hosted within chromite ±olivine. The absence of Pt-Fe alloys and low Pt/Ir in dunite contradict the view that Pt-enrichment of ultramafic rocks is characteristic of Alaskan-type intrusions. This apparent discrepancy is consistent with the positive dependency of Pt solubility on the oxidation state of sulphide-undersaturated magmas. The earliest, high-temperature cumulates of the Polaris intrusion crystallized from strongly oxidized parental magma(s) (log fO2≥FMQ +2). Clinopyroxene- and hornblende-rich cumulates contain low abundances of disseminated pyrrhotite, chalcopyrite, pentlandite, ±bornite, ±pyrite. The sulphide-bearing rocks have primitive mantle (PM)-normalized depletions in IPGE and enrichments in Cu-PPGE-Au, similar to other Alaskan-type intrusions and parallel to PM-normalized concentrations in primitive arc lavas. The absolute abundances, and S-normalized whole-rock concentrations of chalcophile elements in sulphide-bearing rocks, are highest in olivine clinopyroxenites. Several olivine clinopyroxenites have high S-normalized concentrations of PPGE, Au, and Rh that are similar to those of the richest Ni-Cu-PGE deposits (e.g. Noril’sk). Sulphide saturation at the Polaris intrusion appears tied to the appearance of magnetite. A comparison with experimental data suggests that Polaris parental magmas were H2O-saturated, which promoted magnetite saturation at intermediate compositions (MgO ≥5 wt.%). Fractional crystallization of magnetite resulted in reduction of the residual magma to log fO2≤FMQ+1 and induced separation of an oxidized, Cu-rich immiscible sulphide melt.
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