Direct measurement of water loss from isolated podia of Luidia ciliaris under the influence of known levels of hydrostatic pressure has yielded a revised value for the permeability of this structure to water, namely 37.4 x 10-8 cm3/cm2.s.cm H2O pressure. The total fluid loss from a 50 g starfish will therefore be of the order of 0.75 ml/h. The mechanism for the replenishment of this fluid is discussed in the light of the traditional role of the madreporite. It would seem that adequate influx of fluid through this structure has not been observed, neither could it be responsible for ‘topping up’ in the case of arms severed from the parent body which still continue to move for considerable periods.

INTRODUCTION

The nauplius stages of many barnacle species have been described at the light microscope level (Bassindale, 1936; Knight-Jones & Waugh, 1949; Costlow & Bookhout, 1957; Karande, 1974), including those of the British barnacles Balanus balanoides (L.) andBalanus hameri (Ascanius) (Crisp, 1962a, b). Although these studies have included full descriptions of limb structure, it is not possible with the light microscope to resolve the topographical relationship of the limbs and other structures associated with feeding. Attempts to describe the feeding process of barnacle nauplii (Lochhead, 1936; Norris & Crisp, 1953; Gauld, 1959; Moyse & Knight-Jones, 1967) have necessarily been limited for this reason.

The yolk nucleus of Antedon bifida is a large, intensely basophilic structure located in the cytoplasm of small to medium-sized oocytes. Electron microscopy reveals that this yolk nucleus is a conglomeration of hundreds of dense clumps. Each clump, which is a micrometer or two in diameter, consists of finely fibrogranular material in which are embedded ribosome-like particles. Also present in the oocyte cytoplasm are perinuclear dense granules, which may well be the precursors of the clumps making up the yolk nucleus. The yolk nucleus does not appear to participate directly in the elaboration of the yolk granules.

Few investigations into the general biology of associated copepods have been made, although studies dealing with their taxonomy and structure are well documented, for example the many papers of Gotto, Bocquet, Humes and Stock. This work is an attempt to fill certain gaps in our biological information by considering the copepod Paranthessius anemoniae Claus, a cyclopoid associate of the snakelocks anemone Anemonia sulcata (Pennant). First described by Claus (1889) and later by Bocquet & Stock (1959) from Mediterranean waters, Paranthessius has only recently been reported from Irish and British waters (Gotto & Briggs, 1972; Briggs & Gotto, 1973).

The defensive behaviour of 11 species of sea anemone when attacked by the nudibranch Aeolidia papillosa is described. An attempt is made to correlate their defensive responses with the habitat, and with the food preferences of Aeolidia. Actinia equina responds first by tentacle and column retraction, and then by inflation of the column, pedal locomotion, and detachment from the substrate. Anthopleura elegantissima responds in similar ways, but Anemonia sulcata, which has much longer tentacles, uses these in active defence against the eolid. Anemonia also crawls away but it does not detach.

Actinia, Anthopleura and Anemonia are the preferred foods of Aeolidia. They commonly live in dense colonies where locomotion and detachment are likely to result in escape. Tealia felina is less preferred and is much less responsive when attacked by Aeolidia.

Anemones which possess acontia normally eject these when they are attacked by Aeolidia. Although Aeolidia does occasionally eat acontian anemones, evidence is presented which suggests that acontia have some deterrent effect on this predator. Although most acontian anemones are probably able to move by pedal locomotion and to detach from the substrate, these responses are much less frequently given than by Actinia equina.

INTRODUCTION

Dodecaceria caulleryi breeds asexually by fragmentation and regeneration (schizogenesis), and sexually as an epitoke. Fragmentation is initiated in September-November in worms generally more than 40 segments long with the autotomy of the anterior 11–34 segments. Some 14–18 isolated segments are then autotomized in succession from the front of the remainder of the worm, leaving a residual 7–19 posterior segments. The anterior, individual segmental, and posterior fragments produced in this way all begin regenerating; anterior regeneration of the posterior fragment is limited to 14 or fewer segments but posterior regeneration and growth of all fragments is unlimited though slow. When the segmental fragment has regenerated about 7 new anterior and posterior segments, these may be autotomized as secondary individuals and the original segment regenerates again. The anterior regenerate is more commonly shed than the posterior regenerate and not all segmental individuals engage in secondary fragmentation.

Proprioceptive endings associated with the locomotor musculature are apparently extremely uncommon in fishes. Muscle spindles are absent, and only in elasmobranchs have sensory endings of two types been recognized as proprioceptive. One of these, found in sharks, is the coiled corpuscular ending first observed by Wunderer (1908) at the bases of the fins in various species. This type of ending also occurs sub-cutaneously along the body, superficial to the myocommata (Bone, 1964). Lowenstein (1956) examined the responses of the endings associated with the fin bases, and showed that they were slowly adapting mechanoreceptors, functioning as second order proprioceptors since as the fin was bent, so the connective tissue amongst which the endings lie was stretched or compressed, and the receptor discharged.

INTRODUCTION

The development of techniques to culture calanoid copepods over multiple generations in the laboratory has resulted in considerable advances in knowledge about a group of animals of major importance in the marine food web. A series of extensive studies have been made of two species of large calanoids, Calanus helgolandicus (Claus) (Mullin & Brooks, 1967, 1970a, 1970b; Paffenhöfer, 1970, 1971, 1976a, 1976b), and Rhincalanus nasutus Giesbrecht (Mullin & Brooks, 1967, 1970a, 1970b). Feeding, growth, and reproduction have been studied under controlled conditions, using different temperatures, food species, and food concentrations. Some of the information gained in these studies has been incorporated into a simulation model of the planktonic ecosystem of the North Sea (Steele, 1974). However, in the North Sea and in many other sea areas species of small copepod probably form an important component of the food web. Little information is available on the quantitative biology of these small copepods under controlled conditions.

INTRODUCTION

The copepod Temora longicornis Miiller is one of the common zooplankton species in the North Sea and adjacent waters. All developmental stages have been recorded throughout the year off the west coast of Sweden, Temora being considered more common in offshore than inshore waters (Eriksson, 1973). In Loch Striven on the west coast of Scotland it was abundant only in summer, living mainly near the surface (Marshall, 1949). Similarly in the English Channel off Plymouth Temora is present mainly during the summer months (Digby, 1950). T. longicornis was found throughout the year in the Northfrisian Waddensea with temperatures ranging from ca. 1–20 °C (K¨nne, 1952).

The occurrence of Mytilicola intestinalis in populations of mussels in south-west England is recorded and compared with previous data. Since 1955 there have been two main changes in the distribution of Mytilicola: (a) it has invaded all the major estuarine mussel populations on the Bristol Channel coast, and (b) many previously uninfested open-coast populations all round the peninsula are now lightly infested. It is suggested that differences in infestation levels between estuarine and open-coast populations of mussels are due primarily to differences in the degree of exposure to wave action although factors such as size, population density and location of the hosts also influence infestation. The chance of the establishment of breeding pairs of Mytilicola depends on the parasite population size and its distribution through the host population

INTRODUCTION

In an earlier study (Corner et al. 1974) the copepod Calanus helgolandicus (Claus) was found to feed actively on nauplii of the barnacle Elminius modestus Darwin, one adult female ingesting a maximum daily ration equivalent to 25% of the body nitrogen. The present work, in which Elminius nauplii have again been used as a diet, extends the earlier study by determining how efficiently Calanus digests an animal food. In addition, the methods used have provided information on other aspects of carnivorous feeding by Calanus, including the relationship between food concentration and size of ration ingested as well as gross growth efficiency, i.e. the proportion of ingested food invested in growth.

Since the early 1950s a sport fishery for sharks has existed off south-west England. On average some 5000 sharks are taken annually on rod and line between May and October. The catch consists almost entirely of blue sharks, the majority of which are immature or adolescent females, limited numbers of the porbeagle, Lamna nasus Bonnaterre, mako, Isurus oxyrinchus Rafinesque and very occasionally the thresher, Alopias vulpinus Bonnaterre.

There are few teleosts which depart from the ‘classical’ ichthyan body form to such an extent as the seahorse, Hippocampus. In this genus the caudal fin is absent and the tail has become prehensile, the usual function of the caudal fin is taken over by the dorsal and pectoral fins. The dorsal and pectoral fins both have a sculling action, the small anal fin moves ‘bodily’ through the water from side to side.

In the past, interest has generally centred on fast moving fish, which have evolved a limited number of body forms, as few variations are possible without a sacrifice of speed. The evolution of the swimming mechanisms of these fish has favoured an increase in the maximum speed and acceleration. In relinquishing the demands of speed the seahorse has released itself from restrictions which would limit its possible range of form.

INTRODUCTION

Detailed studies of the vertical distribution and migration of the micronekton, plankton and sonic scattering layers in an oceanic environment off Fuertaventura in the Canary Islands were made from R.R.S. ‘Discovery’ during September to December 1965. A general account, including a statement of the objectives of the cruise, has been given by Currie, Boden & Kampa (1969). Foxton (1969) has described the biological sampling methods and techniques utilized. Results of sonic scattering investigations have been published by Blaxter & Currie (1967) and Boden & Kampa (1967). The present study deals only with the pelagic amphipods, and forms a contribution to a series (Angel, 1969; Clarke, 1969b; Baker, 1970; Foxton, 1970a, b; Badcock, 1970; Roe, 1972a, b, c, d; Pugh, 1974) dealing with the distribution and migration of the major taxa sampled during the investigation. An objective summary of the plankton data utilizing factor analysis and cluster analysis has been provided by Angel & Fasham (1973, 1974).

INTRODUCTION

During the last 25 years I have collected opisthobranchs from more than 1200 stations (dredgings, collecting by divers, visits on the tides etc.) all around the Northern Atlantic, and among them close to 200 from the British Isles, viz. during two short visits to Plymouth, two somewhat longer ones to Menai Straits, one to Millport in Scotland, and three to Carna in W. Eire. In all those places, the respective marine stations, leaders and personnel, have been of the utmost help and assistance, and I hereby express my warmest appreciation for the kind way in which I have been received. Without that strong support I should never have been able to accomplish the task of comparing live specimens of opisthobranchs from all around the Northern Atlantic in order to tackle all the taxonomic problems involved. The present paper on the genus Doto is my first separate contribution to a revision of the British nudibranchs. The material obtained is kept in the Zoological Museum of the University of Copenhagen.

In laboratory tanks as well as in the sea Arctica islandica shows a pattern of intermittent burrowing activity. Periods spent at the surface of the deposit alternate with periods buried several centimetres beneath the surface of the sand, during which the animals respire anaerobically. There is no obvious rhythmicity to this behaviour; the duration of periods spent beneath the surface is very variable even in the same animal, but normally lasts between 1 and 7 days.

On the return to aerobic conditions both the heart rate and oxygen consumption areincreased but decline gradually during the following 20–25 h. This increased oxygen uptake is caused primarily by an increase in oxygen utilization but there is little change in ventilation rate. Both the initial rate of oxygen consumption and the duration of the recovery period show a correlation with the duration of the period of anaerobiosis. The concentration of alaninc in the blood of Arctica is high immediately after the return to aerobic conditions but declines during the recovery period. The similarity in the time taken for the concentration of alanine in the blood and the oxygen consumption of Arctica to return to normal levels suggests that at least part of this increased oxygen demand is associated with the metabolism of end-products of anaerobiosis.

INTRODUCTION

This paper forms the second and last part of a study of the vertical distribution and migration of pelagic Amphipoda based on material collected off Fuertaventura, Canary Islands, during the SOND Cruise in 1965. The first part (Thurston, 1976b) dealt with the Gammaridea. The data presented herein deal with the Hyperiidea, to which is added a general discussion.

The background to the cruise has been given by Currie, Boden & Kampa (1969), and Foxton (1969) has described the gear and methods used. This analysis is based primarily on samples obtained from a series of 1 m2 ring-net (N 113) hauls, but has been supplemented by selected materials from modified 3 m Isaacs-Kidd Mid-water Trawl (IKMT), neuston net and 1 m2 Rectangular Mid-water Trawl (RMT 1) hauls. Thurston (1976b) has discussed the limitations of the sampling techniques as they affect the present results.

The filtration rate of Mytilus edulis was measured in a flowing system by estimating the particulate matter concentrations at the inflow (C1) and outflow (C2) of the experimental chamber and immediately surrounding the bivalve (C0). Filtration rate was calculated as R1 = F(C1 – C2)/C0…(1), where F = flow rate through chamber. This formula differs from that previously used in flowing systems (R"t = F(C1 – C1/C2)…(2), by accounting for dilution of inflowing water as it enters the experimental chamber. Formula (1) was used to show that flow rate through the experimental chamber has a negligible effect on filtration rate whereas the use of formula (2) indicates erroneously that flow rate and filtration rate are positively correlated. The particulate matter concentration around the bivalve is also shown to have a negligible effect on filtration rate within the limits tested of approximately 2000–20000 particles ml-1.

This work is the outcome of an undertaking by the Mechanical Engineering Department to repair and if possible to improve a grab used by the Marine Laboratory. The grab was a type which has a good record of effective sampling on coarse hard sediment as reported by Smith & McIntyre (1954) and fully confirmed by our own experience. Its success in these difficult sediments is believed to be due to the initial penetration provided by the spring-propelled jaws and to adequate weight opposing the upward forces as the lifting cable closes them. Because of wear in the cocking mechanism the machine in question had become dangerous to operate and a number of parts had fractured. Improvements to the cocking/triggering mechanism were successful but it was felt that the repaired striking motion would remain prone to further failure by fatigue and wear. A fair degree of mechanical insight was necessary for effective operation and it was considered fairly laborious to use continuously, so the basic problem was reviewed from an engineering design standpoint with attention to the ergonomic and mechanical problems of achieving a quick turnaround in a small boat such as the laboratory's 10 m coble, and to ensuring durability.

INTRODUCTION

The ommastrephid squids are large active animals occurring in most of the world's oceans. Luminous organs or bioluminescence have been observed only in members of the subfamily Sthenoteuthinae, containing the genera Ornithoteuthis, Symplectoteuthis (= Eucleoteuthis), Hyaloteuthis, Ommastrephes and Dosidicus. The light organs of Ommastrephes pteropus are small sub-spherical bodies randomly distributed over the ventral surface of the mantle, head, arms and tentacles (Roper, 1963) and are aggregated dorsally to form a large luminous patch (Clarke, 1965). Relatively little is known about the organs, capabilities and biochemistry of luminescence in cephalopods (Harvey, 1952; Herring, in Press), and the size of the light organ and availability of O. pteropus provide an unusual opportunity for such studies. Although among the molluscs the luminescent systems of the gastropod Latia and the bivalve Pholas have been partially characterized (Shimomura & Johnson, 1968; Henry, Isambert & Michelson, 1970, 1973) the only cephalopod system which has been investigated to date is that of the enoploteuthid Watasenia scintillans (Goto et al., 1974; Inoue et al., 1975). This investigation examines the anatomy and biochemistry of the dorsal light organ of O. pteropus, which differs markedly in these respects from the brachial organs of Watasenia.