Filtering, feeding, and digestion in the lamellibranch Lasaea rubra

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Methods of extraction of the toxin from cultures of Gymnodinium veneficum are described. This is now done by dialysis and evaporation under reduced pressure. The toxin molecule must be large, as it cannot penetrate a dialysis membrane; it is soluble in water and the lower alcohols, but insoluble in ether and chloroform. It is unstable in acids, turning into another toxic product, and is decomposed by hot alkali, though in neutral solution is more or less thermostable. The toxin as it occurs in sea water is not the same as paralytic shellfish poison, but there are some resemblances between this and the 'acid extract', though much more work is needed to check this point.The action of the toxin on a variety of animals is described, and an attempt is made to devise an approximate assay technique using gobies as the test animals.The action has also been observed on a range of isolated preparations, and although the final conclusion as to the mode of action is not quite clear, we feel confident that the site of action in whole animals is in the nervous system, probably acting on ganglion transmission. With regard to the mode of action it depolarizes nerve and muscle membranes. It also abolishes the potential across frog skin without measurably altering the skin resistance.This depolarization probably occurs by interference with the sodium exchange mechanism, allowing rapid entry of sodium into the cells.

Section: Mammaliamentioning

confidence: 99%

The toxin fromGymnodinium veneficumBallantine

Abbott

Ballantine

1957

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“…The method used was that described by Ballantine & Morton (1956), a Harvey light absorptiometer being used to measure the decrease in optical density of an Erdschreiber culture of the diatom Phaeodactylum tricornutum. Each vessel contained 7'5 C.c.…”

Section: Differences In Filtering Behaviour At Different Levelsmentioning

confidence: 99%

The adaptations of Lasaea rubra (Montagu), a small intertidal lamellibranch

Morton

Boney²,

Corner

1957

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A study has been made of the ecology of the small intertidal lamellibranch Lasaea rubra at various tidal levels at Plymouth and Wembury. In addition, experiments have been carried out to investigate physiological and behavioural differences arising from varying amounts of submersion at different tidal levels, and the following findings have been made.During the first hour after their submersion by sea water, L. rubra from high up the shore filter at a rate approximately twice that of animals which live lower down. After 2 h, however, both sets of animals filter at the same rate.High-level animals respond significantly faster to wetting by splash and can tolerate a considerable range of salinity. They also respire at a rate approximately twice that of low-level animals. Respiration, however, is not detectable when the animal is not immersed in sea water.

“…1, column 10). Here, there may have been some small entry of particles such as debris dislodged from the animal's shell; but even after submergence in cultures of the toxic flagellate Gymnodinium veneficum, in which (see Ballantine & Morton, 1956) filtration is prevented, the resecretion of the style was not impeded (Fig. 1, column II Lasaea rubra is without gut phagocytes at any stage.…”

Section: Lasaea Rubra At Various Times Of the Tidal Cyclementioning

confidence: 99%

“…In Lasaea rubra there is evidence, from two sources, of extracellular digestion of other substances as well. First, Ballantine & Morton (1956) have already reported in detail the preliminary digestion of Phaeodactylum (' Nitzschia '), the flagellate Isochrysis, and-more slowly-the diatom Thalassiosira. All these organisms were digested extracellularly within the lumen of the stomach.…”

Section: Lasaea Rubra At Various Times Of the Tidal Cyclementioning

confidence: 99%

The tidal rhythm and action of the digestive system of the lamellibranchLasaea rubra

Morton

1956

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It has been well established that some of the features of the feeding and digestive process in molluscs are rhythmic in character. Notably Hirsch (1915, 1917, 1931) has demonstrated a rhythmic periodicity of secretion in the salivary glands and digestive glands of some carnivorous Gastropoda, and Krijgsman (1925, 1928) has done similar work on the land pulmonate Helix. In all of these animals—and in cephalopods, too, where there is a more elaborate nervous control of secretion—discontinuous feeding is the rule. In the other and perhaps larger category of molluscs—those continuously feeding on fine particles—the central mechanism of the gut is the crystalline style, or its forerunner the protostyle. Here the need is, in Yonge's words (1937), ‘to the extent to which they depend on extracellular enzymes for digestion, continuous secretion’. In Yonge's view, now classical, the style was regarded as ‘an ideal mechanism for the continuous liberation of small quantities of an amylolytic enzyme’. Graham (1939), in his work on style-bearing gastropods, showed that the style is in general confined to animals with a continuous feeding habit, whether by ciliary means or by using the radula to graze on and rasp off fine particles. It is known that style secretion stops and the style is frequentiy dissolved when animals are removed from the water and cease feeding (see Yonge, 1925).