During an examination of the distribution and relationships of muscle receptor organs in the hermit crab, Pagurus bernhardus (Pilgrim, in preparation), it was found that not enough was known about the muscular anatomy of the animal for the experimental work to be described satisfactorily. This paper is therefore an account of the anatomy appropriate to a better understanding of the receptor organs. In the preparation of this account, it was necessary to examine the skeleton of the animal in great detail, since a knowledge of the relationships of especially the movable skeletal parts is basic for an understanding of the muscular system. The study also forms part of a series in which the comparative anatomy of the axial skeleto-muscular systems is examined in the Decapoda. This paper falls naturally into two parts, dealing respectively with the skeleton and the muscles. Although emphasis in this work is on the trunk anatomy of the last six segments of the thorax, it is necessary to extend observations beyond this region for certain interpretations.

All animals do not display the same capacities for repairing injuries, i.e. they possess what may be termed different ‘regeneration potentials’. One parameter influencing the regeneration potential manifested by an organism is its developmental history, or ontogeny. Early in an animal's ontogeny many of its cells are still undergoing both structural and biochemical modifications. As the animal matures, its cells become increasingly differentiated, ultimately attaining a high degree of specialization (Hay, 1966; Balinsky, 1970).

Numerous studies support the contention that the younger an animal ontogenically, the greater is its regeneration potential. Investigations using amphibians have presented several cogent examples of this generalization (Balinsky, 1970). Analogous situations are also evident in the Cnidaria. In the hydrozoan, Hydra, the tentacles contain what are among the ontogenically ‘oldest’ cells in the organism (Tripp, 1928; Brien & Reniers-Decoen, 1949; Burnett, 1966; Campbell, 1967b). Unlike the remainder of the organism, these structures also reportedly possess no regeneration potential (Peebles, 1897; Kanaev, 1952).

Three explanations have been proposed to account for the absence of regeneration potential in isolated tentacles. Nussbaum (cited in Kanaev, 1952) suggested that the absence of interstitial cells in the tentacles precluded regeneration. However, other regions of the animal, when experimentally deprived of this cell type, retained their regenerative capacities (Brien, 1953; Diehl & Burnett, 1964).

A second explanation invoked the size of an isolated tentacle as a factor limiting regeneration. In disputing this suggestion, Peebles (1897) measured tentacle volume. Isolated Hydra grisea (Pallas) tentacles ranged from 0.01 to to 0.03 mm3, while the volume of the smallest body fragment capable of total regeneration was considerably smaller, 0.006 to 0.01 mm3. From these measurements she concluded that the size of isolated tentacles could not account for the inability to regenerate.

The largest recorded specimen of the mesopelagic scyphomedusa, Stygiomedusa fabulosa Russell 1959, was taken in the North Atlantic (49° 53' N, 33° 18' W). Umbrella diameter was 140 cm with an oral arm length of 164 cm. This specimen is morphologically intermediate between the nominal species of the genus, S. fabulosa and S. stauchi. This suggests that S. stauchi is not a distinct species. The midwater fish Thalassobathia peligica was captured in the same haul and could live in association with large scyphomedusae.

The accumulation from sea water of 65Zn, 54Mn, 59Fe and 58Co by the mussel, Mytilus edulis, has been studied in relation to the stable element levels of these isotopes both in the sea water and in individual tissues. For all four radionuclides the greatest accumulation occurred in the stomach and digestive gland samples and further localization of 65Zn and 69Fe was demonstrated by autoradiography. As the animals were starved during the accumulation period the loss of stable elements by individual tissues was also followed. Again the most notable effect occurred in the digestive gland tissues with the exception of a large loss of iron by the foot. Autoradiography showed that after two weeks accumulation 59Fe occurs in large clusters in the foot, notable in the byssus gland area. These clusters disappear after a further two week period and may thus be secreted into new byssus threads.

Studies of the distribution of china clay waste and its effects on the bottom communities off the south coast of Cornwall, initiated by Portmann (1970) and Howell & Shelton (1970), have been supplemented by further surveys, the results of which will appear in future papers by Shelton & Rolfe (in preparation) and Probert (in preparation). This paper describes two polychaete species which have been discovered in this area, namely the hesionid Gyptis capensis (Day) and the ampharetid Sosane sulcata Malmgren. From the zoogeographical viewpoint, the records of both species are of great interest: hitherto, G. capensis was known only from southern Africa and the tropical West Pacific region, and S. sulcata from Scandinavia, West Scotland and the Mediterranean.

Many workers have experienced difficulties in trying to identify species within the genus Enteromorpha. The difficulties arise from our lack of knowledge of the range of variation for the characters used to delimit the taxa and of the sources of the variation shown.

Enteromorpha intestinalis (L.) Link was originally described by Linnaeus (1753) under the name Ulva intestinalis as ‘Ulva tubulosa simplex’ and Enteromorpha compressa (L.) Grev., also by Linnaeus (1753) under the name Ulva compressa as ‘Ulva tubulosa ramosa compressa’. In their interpretations by later authors, the two species differ only in that the former is unbranched and the latter branched. In their cell size, in the unordered arrangement of the cells and in the single pyrenoid in the chloroplast, they seem to belong together. Whether or not a plant is branched would seem to be a straightforward character to use in practice, but for an alga of this kind this is not necessarily so. In its development the unbranched tube of the thallus begins life as a zoospore or zygote which at first divides transversely to form a short uniseriate filament and later by radial longitudinal divisions, the subsequent expansion of which leads to the formation of the hollow tube. In the formation of branches, individual cells, usually towards the base of the frond, divide by a single periclinal division. The outer cell of the pair thus formed then divides transversely forming a single-celled filament, later dividing by radial longitudinal divisions and repeating the structure of the main axis.

The buoyancy, lipid levels, and orientation of five species of myctophid from the Biscay area were examined, and it was found that two of the five were probably normally denser than the sea water in which they live. Analysis of the swimbladder gas of Myctophum punctatum collected at the surface at night indicated that this species has a less extensive vertical range in this area than elsewhere. A functional classification of myctophids is proposed, based upon density, lipid levels, and the presence or absence of a gas-filled swimbladder.

A comparison has been made between the concentrations of eleven trace metals in the tissues of two species of scallops, Pecten maximus (L.) and Chlamys opercularis (L.), collected from the same area of the English Channel. Although there was considerable variation between individual animals, the mean concentrations of Ag, Co, Cr, Cu, Mn, Ni, Pb and Zn were higher in the whole body of Chlamys than in Pecten but concentrations of Al, Cd and Fe were lower. In both species, seasonal changes in the concentrations of Co, Cu, Fe, Mn, Ni, Pb and Zn were observed and, in general, the highest values were found in the autumn and winter months. These changes may be related to food supply, since concentrations were generally highest when phytoplankton productivity was low and tended to fall in the spring as productivity increased rapidly to its annual peak. Despite problems arising from individual and seasonal variation, the kidneys and digestive gland of scallops appear to have potential as biological indicators of trace metals.

The results obtained for Pecten and Chlamys are compared with those in the literature for species from the family Pectinidae.

The movements of herring and plaice larvae of different age, from hatching to about 8 weeks old, were monitored at different levels in a vertical tube by means of matched pairs of thermistors controlled and ‘balanced’ by bridge circuits. Movement of larvae past the thermistors upset the balance and the resulting change in the circuit could be followed on a pen-recorder. Having established, by visual comparisons, the interpretation of the pen record, experiments could be performed over extended periods or at low light intensities when visual observations would have been tedious or impossible. The numbers of larvae present were shown by the number of spikes on the pen record per unit time, while a measure of their size or activity was given by the height of the spikes.

The light intensity could be altered by interposing neutral-density filters between an artificial light source and the surface of the tube. Alternatively, natural daylight could be beamed in by a mirror above the tube when placed by a window. Using artificial light, changes of very large intensity had little effect on the larvae until a critical level was reached (equivalent to the intensity at late dusk or early dawn) when a vertical migration took place. A similar vertical migration took place when the natural light at dusk was beamed in; many larvae then moved to the surface and remained there, apparently very active throughout the night untill the light increased at dawn. Vertical migration could be simulated in the laboratory at any time by imposing an artificial light-cycle of appropriate amplitude on the larvae.

An opening and closing net system is described in which 1 m2 and 8 m2 rectangular trawls are combined in the same framework; details of the acoustic telemetering and release equipment are included. A brief account of the application of the rectangular system to larger and to more specialized trawls is given.

Pogonophora are long thin tube-dwelling invertebrates similar in size to polychaetous annelids, but lacking both mouth and gut, and found mainly in the deep sea. Current discussion of their systematic position had revealed a need for more information about particular aspects of their morphology and embryology (Southward, 1971a). The earlier attribution of Pogonophora to the echinoderm-chordate group, Deuterostomia, based mainly on their apparently tricoelomate structure, has been questioned recently, following the discovery of the previously unknown posterior end (Webb, 1964a; Ivanov, 1965). This posterior end is a small and delicate structure composed of several coelomate segments separated by septa and provided with short bristles. It has such a strong resemblance to the posterior end of an annelid, though of course it does not contain a gut, that there has been much speculation about the possibility of a relationship between Pogonophora and Annelida and some reconsideration of the features thought to indicate affinity to the Deuterostomia (Livanov & Pornrieva, 1967; Webb, 1969b; Ivanov, 1970; Norrevang, 1970a, b; Southward, 1971a).

The type species of Platychrysis, P. pigra, was described by Geitler in 1930 from a sample taken at Las Palmas in the Canary Islands (Geitler, 1930). It was later recorded by Carter in 1937 from a brackish pool at Bembridge, Isle of Wight, and a more complete description of the species was given, including a description of the motile cells (Carter, 1937). A taxonomic comparison of the three genera Prymnesium J. Massart, Chrysochromulina Lackey and Platychrysis Geitler was published by Conrad (1941), whose Belgian records for the species (Lilloo) were subsequently published in 1954 (Conrad & Kufferath, 1954). In 1967, Norris (Norris, 1967) described a new species, P. neustophila, recorded from Puerto Peñasco (Mexico), but this species needs further investigation since the account is somewhat incomplete.

A number of workers have studied the uptake of zinc by algae, but the mechanisms of uptake are not fully understood. Broda, Desser & Findennegg (1964) concluded that 65Zn uptake by Chlorella was a passive process since it was affected neither by metabolic inhibitors nor by anaerobic conditions. In later papers, however, Broda and co-workers (Matzku & Broda, 1970; Findennegg, Paschinger & Broda, 1971) have concluded that 65Zn uptake occurs both by a rapid passive process of ion-exchange and also by a slower, metabolically dependent process. Bachmann & Odum (1960) showed that65Zn uptake by Chaetomorpha was stimulated by light and they concluded that uptake was a metabolically active process. Gutknecht (1961,1963) showed that uptake of65Zn by Viva and Porphyra was stimulated by illumination and by increase in temperature. He also showed that increase in pH of the surrounding medium increased65Zn uptake and thus concluded that65Zn uptake was a passive process which was affected indirectly by metabolism.

The tunicate heart has been extensively studied, with particular recent emphasis on the physiology of heart reversal (see Krijgsman (1956) and Kriebel (1968) for reviews). The salp heart, however, has received much less attention (Schultze, 1901; Nicolai, 1908), mainly because of the difficulty of maintaining this delicate marine animal in the laboratory. Thus the structure and function of the salp heart has been assumed to be similar to that of the sessile tunicates (Ihle, 1935; Berrill, 1950).

1. The data for five planktonic taxa sampled during the SOND cruise (autumn 1965) by R.R.S. ‘Discovery’ in a day and a night series of horizontally towed nets have been analysed by factor and cluster analyses.

2. The factor analyses of hauls showed that there were five biologically distinct zones in the water column between the surface and 1000 m. The zones were more distinct in the day series than in the night.

3. Factor analyses of the individual taxa gave sensible groupings of species and the factor score plots gave ‘averaged’ depth distributions for each group.

4. Cluster analyses of the individual taxa gave results consistent with the factor analyses. Both methods gave groupings which fitted the zonation patterns of the hauls, except for the two zones between 100 and 460 m at night.

5. Only cluster analyses could be carried out on the total data matrices. Although satisfactory interpretation was only possible with the aid of the analyses of the individual taxa, the zonation and species groupings were again largely retained.

6. The zonation of the planktonic taxa is shown to be very similar to that described for nektonic species sampled on the same cruise.

7. The usefulness of these analytical methods is compared with the conclusions of other investigators. It is concluded that the rotation of the matrices to simple structure in the factor analysis gave a marked improvement in the ease of interpretation.

8. For this data, principal component analyses gave very similar results to the full factor analyses.

Neutral lipid classes were analysed in the livers, muscles and sera of Deania, Centroscymnus, Squalus and Prionace. All three squaloid sharks contained triglycerides and alkyldiacylglycerols and the two deep sea squaloids contained additionally hydrocarbons. Prionace contained triglycerides and hydrocarbons but no alkyldiacylglycerols. For a given species the class compositions of the lipids were similar in liver, muscle and serum, except that serum contained additionally cholesteryl esters and wax esters. Cholesteryl esters in Squalus serum were rich in oleic acid whereas wax esters were very rich in polyunsaturated fatty acids. Squalus serum contained a major and a minor lipoprotein species both of which transport all four neutral lipids in serum. It is concluded that, with the exception of cholesteryl and wax esters in serum, neutral lipids are distributed between shark tissues by a mechanism that is relatively non-specific with respect to lipid class.

It is usually very difficult to obtain knowledge of predator-prey relationships in the marine plankton. However, because of the very specialized nature of this relationship, where the copepod spends part of its life as a parasite and part of its life as a predator, detailed understanding of the relationship has been obtained from both laboratory and field observations.

The usual concept of predation involves a predator which is the same size or larger than its prey. This prompted Foxton (1966), in discussion of the large salp Salpa thompsoni, to consider only the gut contents offish, sea birds, seals, etc., when analysing data on predation. He noted that considerable mortality occurred between the embryos and the adult stages which did not appear to be explained by the data on predators which he considered. He concluded that ‘further study is necessary before (the salp's) true role can be defined’.

Copepods and amphipods are often associated with salps in distribution (Hardy, 1936), usually being regarded as parasites (Furuhashi, 1966; Wolfenden, 1911). Amphipods which lay their eggs directly into the living tissue of salps have been described (Haruhiko, 1967), while the use of the salp test as a protective house by the amphipod Phronema is well known (Hardy, 1956).

Dense swarms of Thalia democratica occurring in S.E. Australian waters are often associated with high densities of Sapphirina copepods (Dakin & Colefax, 1940; Thompson, 1948; Sheard, 1965). Observations of these swarms underwater, by the author, show the presence of many Sapphirina copepods inside salps in the undisturbed state, as in Plate I (A).

At the present time only limited data about the release of organic matter by phyto-plankton in the marine environment are available (Antia, McAllister, Parsons, Stephens & Strickland, 1963; Fogg, Nalewajko & Watt, 1965; Hellebust, 1967; Jitts, 1967; Home, Fogg & Eagle, 1969; Anderson & Zeutschel, 1970; Thomas, 1971; Samuel, Shah & Fogg, 1971).

A series of controlled, labelled feeding experiments were carried out on Neomysis integer in order to investigate its lipid metabolism. The techniques of thin-layer chromatography, preparative column chromatography, analytical and preparative gas-liquid chromatography and low-background 14C counting were used to follow the incorporation of a 14Clabelled fraction from a range of diets into the animal's lipid. Neomysis integer was found to be capable of converting dietary starch or short-chain saturated fatty acids to longchain polyunsaturated fatty acids, which were then incorporated into the TG and PL fractions.