James D Robertson

Ionic regulation in the crab Carcinus maenas (L.) in relation to the moulting cycle

Abstract The concentration of the principal ions, sodium, potassium, calcium, magnesium, chloride and sulphate in the blood-plasma of Carcinus maenas have been measured and compared with those of sea water in which the crabs were kept. Taking the total ionic concentration of sea water as 100, the mean values with standard errors for the plasma at different stages of the moulting cycle are as follows: intermoult 100·±0·26 (N = 19), premoult 107·5±1·00 (5), postmoult within 24 hr 102·9±0·56 (7), postmoult 2–14 days 98·2±0·37 (6), moulted several months 100·3±1·5 (2). Increases of sodium, calcium, magnesium and chloride are responsible for the rise in total concentration in the premoult stage; calcium increases from 126 per cent to 164 per cent of the sea water value, magnesium from 37·1 per cent to 55·5 per cent. Measurements of total particle concentration by the Krogh-Baldes method show the same pattern as the chemical estimations. From the concentrations of non-protein amino-N, lactic acid, reducing sugar, ammonium, inorganic phosphate and bicarbonate in the plasma, it is improbable that at any stage each of these constituents (except bicarbonate) contributes more than 2–3 millimoles or mg ions to the osmotic concentration (the latter is about 1080 mg ions/kg water at the intermoult stage). Uptake of ions and water in intermoult Carcinus, balanching losses in the antennal secretion and by outward diffusion, probably takes place chiefly through the gills. Uptake of water at moult, averaging 66·3 per cent (range 43–96) of the premoult weight, takes place through the foregut and hepatopancreas. Chemical analyses show that the fluid absorbed is essentially sea water, with all its ions. Absorption of water into the extracellular fluid halves the concentration of blood protein. About on third of the water is absorbed intracellularly. Extracellular volume in intermoult crabs, as determined by the distribution of injected sucrose and inulin, averages 32·6 ml per 100 g (30·2–34·9 ml in four estimations). Hepatopancreatic secretion differs inorganically from plasma in having higher potassium, calcium and magnesium concentrations. During the postmoult phase, when sea water is being absorbed, all the ions of the secretion except chloride are higher than those of the plasma, sulphate being thirty times as high. Sulphate accumulates owing to the slowness of its absorption compared with the other ions present in sea water.

THE HABITAT OF THE EARLY VERTEBRATES

1 On geochemical grounds it seems that the early Ordovician seas were very similar in salinity and ionic composition to seas at the present time. Physiological speculations based on the assumption of dilute sea water in the Ordovician oceans, especially those which relate the level of salts in vertebrate blood to that of these seas, are invalid. The first marine and freshwater vertebrates were probably subjected to the same physicochemical environmental stresses which affect present‐day fishes and the lower marine chordates. 2 The earliest vertebrate remains are from the Ordovician and include problematical fish‐jaws (from Missouri, U.S.A.), plates and scales of heterostracans and coelolepids (from Colorado, U.S.A.), and teeth of acanthodian fish (from the neighbourhood of St Petersburg, Russia). All these remains are from marine sediments, associated with typical marine invertebrates in the first two cases. 3 Ostracoderms and placoderms have been found in Silurian strata (including the Downtonian) in eight countries of Europe and in North America. The fossils comprise heterostracans, coelolepids, anaspids, osteostracans, acanthodians and arthrodires. Associated marine invertebrates are found with the vertebrate fossils in the vast majority of the records, and in no case is there any evidence that the ostracoderms and fishes lived otherwise than in the sea. 4 Ostracoderms and bony fishes are represented in both marine and freshwater deposits of the Devonian period. 5 A marine origin for the vertebrates is supported by the fact that the three protochordate groups, Hemichordata, Urochordata, and Cephalochordata, are marine. 6 The members of the marine order Myxinoidea of the Cyclostomata have an internal medium of high salt concentration, equivalent to that of the surrounding sea water, a feature found in the lower chordates and in marine invertebrates. This may well be a primary feature, derived directly from marine chordate ancestors. 7 Consideration of the glomerular kidneys of the marine myxinoids and elasmo‐branchs, forms with blood isosmotic with sea water, and of the kidneys of other fishes, leads to a rejection of the view that such kidneys are a freshwater adaptation which has arisen in some freshwater protovertebrate. Glomerular kidneys probably existed in marine protovertebrates, and subsequently became a useful preadaptation for life in fresh water. 8 The arguments deemed to support a freshwater origin of vertebrates have been considered and rejected on the grounds that some are erroneous and others improbable. Palaeontological and physiological evidence leads to the conclusion that the vertebrates were originally a marine group.

Osmotic constituents of some echinoderm muscles

Abstract 1. 1. The muscles of the holothurian Parastichopus tremulus and the echinoids Echinus esculentus and Strongylocentrotus droebachiensis have been analysed and compared with the perivisceral fluids bathing them. 2. 2. Inorganic ions and phosphates account for 60–69% of the osmotic concentration, the balance being predominantly free amino acids in the echinoids and amino acids and betaine in the holothurian. 3. 3. The phosphagen in Parastichopus is arginine phosphate, but the echinoids have both arginine and creatine phosphates.

Osmotic constituents of the blood plasma and parietal muscle of Scyliorhinus canicula (L.)

Abstract 1. 1. The principal osmotic constituents of plasma and muscle have been determined, 17 and 22 respectively. 2. 2. Specimens from Plymouth and Millport areas were isosmotic with sea-water within 1%. Fluid ultracentrifuged from muscle was 6% (5–8%) hyperosmotic to plasma, presumably due to some breakdown of labile constituents. 3. 3. Calculated osmolalities using osmotic coefficients agreed reasonably well with the direct measurements.

The composition of blood plasma and parietal muscle of oslo fjord eels [Anguilla anguilla (L.)] and the river lamprey [Lampetra fluviatilis (L.)]

Abstract 1. 1. The principal osmotic constituents of eel and lamprey parietal muscle have been determined and summations of ions and nitrogenous constituents compared with those in the plasma. 2. 2. By ultracentrifuging eel muscle, analysing the muscle fluid and centrifuged muscle, and determining their extracellular fluid (inulin space) ion-binding in the cells was estimated as Na 60%, K 4.6%, Ca 67%, Mg 28%, Cl 46% and P 1.3%. 3. 3. Calculated osmolality of muscle exceeds that of the plasma, and this is discussed in relation to binding and other factors.

The osmotic concentration of parietal muscle of the hagfish Myxine glutinosa L., including estimates of free and bound constituents

The principal osmotic constituents of plasma and of muscle before and after ultracentrifugation have been determined. By analysing the muscle fluid and centrifuged muscle and determining their extracellular fluid (inulin space), ion-binding in the cells was estimated at Na 26%, K 0.3%, Ca 93%, Mg 24%, Cl 21% and P 10%. Muscle fluid was 4.9% (2.7-7.4%) hyperosmotic to plasma. This is discussed in relation to calculated osmolality of muscle and plasma.

The free amino acids in muscle of three marine invertebrates Nephrops norvegicus (L.), Limulus polyphemus (L.) and Eledone cirrhosa (Lamarck)

Abstract 1. 1. The highest concentrations of amino acids were found in Nephrops and Eledone, with mean values of 481 and 345mmol/kg water, respectively. 2. 2. Arginine, taurine, proline and alanine were among the six highest amino acid concentrations in the three species, making up 82–98% of the totals, the lowest concentration being that of Limulus in concentrated sea-water. 3. 3. Total amino acids are considered from the point of view of osmotic concentration in relation to other nitrogenous compounds of muscle.

Ionic composition of the coxal gland secretion of Limulus polyphemus

Abstract 1. 1. The concentrations of ions in the coxal gland secretion have been determined and compared with those in the plasma. 2. 2. High values of magnesium and sulphate in the secretion are correlated with the reduced values of these ions in plasma compared with sea-water

Osmotic constituents of the body-wall muscles of the hemichordate Balanoglossus clavigerus, the tunicate Ciona intestinalis, and the cephalochordate Branchiostoma lanceolatum

Abstract 1. 1. The body-wall muscles have been analysed for inorganic and nitrogenous constituents, 20 in all. 2. 2. The proportion of ions to nitrogenous constituents is highest in Ciona muscle which has the lowest amino acids and creatine of the three, Balanoglossus and Branchiostoma are very alike in composition, except for much higher phosphorus and creatine in the latter. 3. 3. Calculated muscle osmolality has been compared with directly determined osmolality of fluid centrifuged from muscle in Ciona and Branchiostoma . 4. 4. Phylogenetic implications of the phosphagens and other features are discussed.

The free amino acids of muscle in the cephalochordate Branchiostoma, the cyclostome Myxine and some fishes

Abstract 1. 1. Branchiostoma and Myxine have the highest concentrations of amino acids (207 and 234 mM) of the five species investigated. 2. 2. The predominant amino acids are glycine, proline, alanine, taurine, serine and valine, which form 83–98% of the total, except in Latimeria (60%). 3. 3. Total amino acids are considered from the point of view of osmotic concentration in relation to other nitrogenous compounds of muscle.