Search

Mulinia edulis and Mytilus chilensis are suspension-feeding bivalves with homorhabdic gills that live in different sedimentary habitats in the lower and upper intertidal, respectively, in Yaldad Bay, Chile. They are faced with different suspended particle size distributions when feeding, and both eliminate most of the inorganic particles by pseudofaeces production. This study used histology, scanning and transmission electron microscopy, and video endoscopy to compare particle processing on the labial palps and the mechanisms of particle sorting, acceptance, and rejection in the two species. In both species, disaggregation of mucus-bound particles occurs on the plicate surface of the palps. Particles destined for ingestion pass anteriorly from crest to crest and reach the mouth via the palp acceptance tract. Those destined for rejection enter the troughs between the plicae and move ventrally to the palp rejection tract. The palps manipulate the pseudofaeces into a mucous ball, which is transferred to the mantle rejection tract. In Mulinia edulis (an infaunal, siphonate mactrid), the pseudofaeces are stored in a chamber at the base of the inhalant siphon until expelled by intermittent contraction of the siphon wall. In contrast, Mytilus chilensis (an epifaunal, non-siphonate mytilid) releases pseudofaeces continuously when submerged., Introduction The quality and quantity of the seston in the water column in coastal environments such as estuaries, intertidal flats and salt marshes can vary considerably on various time scales [...]

The influence of the spherulite size and distribution on the fracture toughness and Izod impact strength at different temperatures of controlled-rheology polypropylenes with 0, 154, 402, and 546 ppm of peroxide has been evaluated. As the peroxide content increased, the average spherulite size was enhanced and the distribution width reduced. The fracture toughness and the Izod impact strength were lowered with the peroxide content due to the diminution of the amorphous interconnections among the crystalline regions. Porosity seems to control the fracture behavior for the materials with the highest peroxide content. Besides, a considerable loss of ductility was observed ahead of the stable crack growth zone. Below the glass transition temperature, the impact strength underwent a sudden drop with the temperature, more remarkable as the molecular was higher. The main mechanism of deformation and failure consisted on the formation of crazes, stretch out, and a final collapse through the interspherulitic zones. POLYM. ENG. SCI., 52:805-813, 2012. ©2011 Society of Plastics Engineers, INTRODUCTION Low manufacturing costs, ease of recycling, and possibility of tailoring properties are some of the reasons why isotactic polypropylene (iPP) has exhibited a fast growth in consumption since its [...]

Sessile females of the gastropod Crepidula fecunda are exclusively suspension-feeders. Our previous work showed that particles removed from suspension are entrained on the gill and continuously accumulate as a mucous string on the distal margin of the lamella, although some are transferred by a ciliary tract to the food pouch, where they form a mucous ball. The mucous string is transferred from the gill margin to the neck canal, where it forms a mucous cord which is transported to the mouth. The mucous ball and the mucous cord are ingested with the aid of the radula. In this study we examined the response of the system to a wide range of cell concentrations of the flagellate Isochrysis galbana. As the particle concentration increased from 5,000 to 200,000 cells [ml.sup.-1], the volume of the mucous ball almost doubled, as did the number of radular extrusions required to ingest it. The total volume of mucous balls produced and ingested increased very slightly as particle concentration rose from 5,000 to 100,000 cells [ml.sup.-1], but the volume of mucous cord material ingested increased four to five times over the same range. At higher food concentrations the mucous cord increased in thickness, but not in length, which is constrained by the length of the gill margin. At all particle concentrations the mucous cord accounted for 80-95% of the total material (mucous cords plus mucous balls). Ingestion rate reached a maximum at 140,000 cells [ml.sup.-1] for mucous balls and mucous cords. At higher concentrations the production of pseudofaeces increased from all sources ('type-I' pseudofaeces from rejected mucous balls; 'type-II' pseudofaeces from rejected fragments of mucous cords; and 'type-III' pseudofaeces, which come from particles trapped in a coarse mucous net at the mouth of the inhalant mantle cavity and are transferred via the lateral ciliary tract to the mantle margin, by-zpassing the food pouch). Thus C. fecunda has adopted a feeding strategy in which particle entrainment by the gills is continuous, even at very high ambient particle concentrations (200,000 cells [ml.sup.-1] for I. galbana), and excess material which cannot be ingested is rejected by one or more of three routes for the elimination of pseudofaeces., Introduction Intertidal organisms are exposed to considerable variations in the physical and chemical environment, not only between locations but also during the tidal cycle (Sanders 1968, 1969; Slobodkin and Sanders [...]

The response of digestive enzymes to variable nutritional conditions over a 7-day acclimatisation period in epifaunal (Mytilus chilensis) and infaunal (Mulinia edulis) bivalves were determined. This study has established that the cellulase complex was the most important enzyme in the digestive gland and the crystalline style of Mytilus. In Mulinia, protease and laminarinase were prominent in the digestive gland, and laminarinase, in the style. The enzyme activity in M. chilensis was markedly different between its original habitat (tidal flat) and following a period of acclimatisation in a subtidal habitat, and showed increases in all specific and total digestive enzyme activities. However, transplant to a subtidal habitat affected the enzyme system in Mulinia in different ways. The differences observed in enzyme behaviour in response to variable feeding conditions reflected a more rapid adaptation of the epifaunal species (Mytilus), whereby over a 7-day period enzyme production increased in response to an improvement in feeding conditions. Enzyme response was less noticeable in the infaunal species (Mulinia).

Research was conducted to examine the regulatory transposition in the chimera of mammalian guanylyl and adenylyl cylases (GC/AC chimera) by coexpressing guanylyl cyclase and adenylyl cylase halves. Results demonstrate the ability of functional complement at the catalytic sites in both cyclases. Findings obtained from the enzymatic characterization of the chimeric cyclase suggest an important role of the N-terminal adenylyl cyclase half for stimulatory actions.