Cadlina laevis (L.) is the first British species of nudibranch shown to possess direct development. The embryo leaves the egg-capsule approximately 50 days (at 10° C) after oviposition, and resembles the adult in the general form of the body. Sufficient food reserves remain to sustain life and apparent growth for more than 1 week of benthic life. A vestigial veliger phase is passed through within the egg-capsule. The shell, velum, mantle, and metapodium-rudiment resemble transitorily those organs of opisthobranch veliger larvae, but certain veliger structures (larval kidney, velar locomotor and pedal cilia) are vestigial in Cadlina, and others are altogether absent (operculum, larval retractor muscle, subvelar ridges, metapodial mucus-gland, pedal sensory cilia, and nephrocysts).

In the Opisthobranchia three distinct development types can be recognized. Type 1 includes those species which possess planktotrophic veliger larvae. Type 2 comprises the species which have lecithotrophic larvae (in the sense employed by Ockelmann, 1965). Type 3 species have direct development, in which many veliger structures may be briefly recapitulated before hatching. Species of type 3 possess eggs of the largest sizes, species of type 2 in general have smaller eggs, while species of type 1 possess the smallest eggs. There is a positive correlation between egg size and the length of the embryonic period, and an inverse correlation between both and batch size. Within any development-type, the largest species tend to produce larger eggs in greater numbers. Within any species, the largest individuals tend to produce more eggs than do the smaller individuals; egg size varies little through the geographical range.

An accurate, dependable determination of 0–60 μg-at./l. of NO−3-N in sea water has been developed. The sample is treated with tetrasodium ethylenediaminetetraacetate solution and passed through a column of copperized cadmium filings. A nearly quantitative reduction of nitrate to nitrite results. Nitrite is then determined by a diazotization method. Neither sulphide nor high nitrite concentrations interferes. Approximately eight samples per hour per column can be analysed with a standard deviation of 0.12 μg-at./l. at the 20 μg-at./l. level.

Introduction

Accurate determinations of nitrate ions in sea water have been difficult, especially under shipboard conditions.

The colorimetric method described by Harvey (1926, 1930) and improved by Cooper (1932), Zwicker & Robinson (1944), and others uses strychnidine in concentrated sulphuric acid to produce a red colour. The reagent lacks reliable sensitivity, because it is dependent on the rates of mixing and cooling.

In a method by Armstrong (1963), the absorbance of nitrosyl chloride in the UV region is measured with a spectrophotometer. While the method is good for small samples containing high concentrations of nitrate, the use of concentrated sulphuric acid and lack of sensitivity limit its use in routine analysis.

A method in which nitrate is quantitatively reduced to nitrite would be advantageous, because nitrite can be readily determined by the sensitive diazotization method proposed by Griess (1879). Several such methods have been proposed. FØyn (1951), Vatova (1956), and Chow & Johnstone (1962) used zinc powder for the reduction, but the reduction is sensitive to temperature, and it is necessary to centrifuge or filter each sample.

The pigments of the polychaete Sabella penicillus L. were reinvestigated. In addition to zeaxanthin and traces of lutein, a series of carotenoids which may represent steps in the formation of canthaxanthin have been found. These are β-carotene, isocryptoxanthin, echinenone, 4-hydroxy-4′-keto β-carotene and canthaxanthin. No astaxanthin was found. In two other sabellids, Myxicola infundibulum (Renier) and Megalomma vesiculosum (Montagu), astaxanthin was confirmed as the major pigment and the presence of echinenone was established. Attention was drawn to the similarity of the pigments of Sabella penicillus with those of other invertebrates and it has been suggested that in invertebrates a common pathway for the formation of canthaxanthin may exist.

Eggs of plaice, Pleuronectes platessa L., were incubated in salinities of 5, 17.5, 35 and 50%. After fertilization a large concentration difference is maintained between the yolk and the external medium; this difference is present throughout development. The unfertilized egg becomes isosmotic with the medium within 24 h.

High mortalities were found at all stages of development in salinities below 17.5% most eggs died in the blastula or early gastrula stages. In addition, mechanical disturbance (e.g. during transport) also led to many deaths at this stage.

Water movement could occur between the environment and both the yolk and embryonic cells, it was detected by changes in the freezing-point of the yolk and changes in the volume of the blastula cells.

After hatching, the yolk-sac larvae tolerated salinities of 15–60% for 1 week, and the body fluid concentration was regulated within fairly narrow limits in these salinities. After metamorphosis, tolerance to high salinities was less (45% for 1 week), but tolerance and regulation in low salinities was greater (2.5% for 1 week). It is suggested that functional changes in the epidermis and kidney underlie these changes in tolerance.

Introduction

An investigation of the effects of salinity on the early development of the herring (Holliday & Jones, 1965) suggested that the ability to osmoregulate was present in the cells of the early blastula, but not in the vitelline membrane of the fertilized egg. The yolk was not fully regulated until gastrulation was complete; until this time it was approximately isosmotic with the medium in which it was being incubated.

Larvae of Branchiostoma lanceolatum (Pallas), of a late pre-metamorphosis stage and characterized by a bright fluorescent green around the ilio-colonic ring, were taken in the Plymouth area plankton in August 1965.

Adults were kept in 0.04% thiouracil to determine the general effect at this concentration. It was lethal over a period of weeks.

The larvae were kept in the dark at a constant temperature of 10° C, individu-ally or in pairs, in 0.04%, 0.02%, 0.01%, 0.005% and 0.0025% thiouracil, in saturated solutions and suspensions of thyroxine and triiodothyronine, and in ordinary sea water. Solutions were changed weekly. The flagellate Dunaliella primolecta Butcher was supplied as food.

All the larvae metamorphosed at approximately the same time and rate, two exceptions being that 0.04% thiouracil was a more obviously toxic concentration and the thyroxine and triiodothyronine larvae were rather more precocious in their metamorphosis.

It is suggested that metamorphosis is a ‘triggered’ process and is self-sustaining. Thus once it has begun it cannot be delayed or accelerated significantly. All the larvae caught were at a stage when this ‘triggering’ had been released.

It is considered possible that the metabolism of the larva and the initiation of metamorphosis is controlled by a secretion of the club-shaped gland.

INTRODUCTION

The position of the amphioxides larva has already been discussed (Wick-stead, 1964). No clear demarcation could be made between the usual type of acraniate larva and amphioxides. It was suggested that the amphioxides was a giant larva, a phenomenon not uncommon in oceanic plankton.

Introduction

The position of the amphioxides larva has already been discussed (Wickstead, 1964).

The physiological basis for the previously reported differences in the rate of respiration between high-shore-level and low-level populations of Patella vulgata in the summertime has been investigated in relation to distribution differences between this species and P. aspera.

The respiration rate of both P. aspera and low-level P. vulgata is low in the winter but increases in the spring to a level which is maintained until the post-spawning period in the autumn. The respiration rate of high-level P. vulgata does not increase in the spring but remains at the low winter level. The inter-population difference in rate of respiration therefore appears in the spring and is maintained until the autumn.

The difference in rate of respiration cannot be accounted for by differences in the amount of non-respiring tissue in equal weight individuals and is phenotypic and not genotypic, as indicated by transplantation experiments. These experiments also rule out the possibility of differences in age of equal weight individuals from the two populations being responsible.

Respiration rate was found to be a function of both intertidal height and of the abundance of algal food in the habitat. It is suggested that the low-level population of P. vulgata should be regarded as the normal form and that the low respiration rate of high-level limpets in the summer represents a form of adaptation to the stresses of their habitat. It is possible that both nutritional level and temperature acclimation are important in this, and it is speculated that inability to reduce the level of metabolism may be one factor preventing the colonization of high-shore-level habitats by P. aspera.

Investigations showed that populations of Cirriformia tentaculata (Montagu) at Plymouth, Coverack and Salcombe produce both free-swimming and demersal larvae from single egg batches. The proportion of free-swimming to demersal larvae varies from one brood to another but is constant in different cultures from a single brood. Control of the proportion in which the two behavioural types are produced appears to be genotypic and not phenotypic. The larval types could not be separated morphologically but additional evidence for the existence of polymorphism in the species was provided by the variation of esterase pattern between adults. The population that existed in Southampton water previous to the winter of 1962/63 and which produced only demersal larvae was probably genetically isolated from other populations of the worm and showed behaviour atypical of the species as a whole.

Introduction

Since the publication of a note reporting behavioural differences existing between the larval stages of Cirriformia tentaculata (Montagu) from Southampton Water and from Plymouth Sound (George, 1963), continuing investigations have shed more light on the problem. Observation of the Southampton population from 1959 to 1962 showed that demersal larvae were produced throughout the breeding season, from May to September (George, 1964a), whereas Wilson (1936) found that a population from Drake's Island, Plymouth Sound, produced a free-swimming larval stage in July of 1928 and 1933. It is known that some species of polychaete produce pelagic and non-pelagic forms according to the time of year (Mesnil & Caullery, 1917; Thorson, 1946). The Plymouth population was therefore re-examined to determine whether free-swimming larvae were produced during the entire breeding season.

Annual surveys carried out in south-west England since 1949 show that the arctic-boreal barnacle, Balanus balanoides, which was uncommon or rare in i960, has increased greatly in abundance during the colder years since then. Its numbers now approach those recorded in the 1930's, and there has been a corresponding reduction in abundance of the warm-water species, Chthamalus stellatus.

The endogenous tidal rhythm of the littoral fish Blennius pholis L. was studied in the laboratory. It was found that there was no difference in the mean level of activity of fish caught on spring and neap tides. The time-interval between activity peaks (the period length) gradually increased in constant darkness. A similar, although not significant, increase was also observed in continuous illumination.

There was no evidence of any diurnal component in the rhythm, but freshly caught fish subjected to alternating periods of light and darkness, equal in duration to the natural period, responded to the onset of illumination by greatly increased activity only when the light period began between activity peaks.

Fish which had been kept in the laboratory for several weeks and had lost their natural rhythm still responded to light by increased activity. This increase was not as great as that shown by freshly caught fish, however, and the response decreased with time. Evidence of re-entrainment of the natural rhythm after 7 days in alternating periods of light and darkness was not found. It was shown that feeding the fish half-way through the 12 h light-period resulted in a reduction of activity after feeding. This did not occur when the fish were fed half-way through the dark period.

A 4h cold shock of 10° C resulted in partial re-entrainment of rhymthic activity in B. pholis.

B. pholis, which alone appears to have a persistent rhythm, differs from certain other fish examined in its strictly littoral habitat and its possible need for activity periods synchronized with the tide.

A study has been made of the nitrogenous compounds excreted by Calanus helgolandicus (Claus) collected at Plymouth.

Most of the excreted nitrogen is in the form of ammonia which accounts for 60–100% (average 74.3%) of the total, and some of the remainder may be lost as urea. There is no evidence for the excretion of measurable amounts of amino acids.

Whether the animals are starved or fed they are primarily ammonotelic, and the quantity of ammonia produced at 10° C (3.33 μg/g. dry body wt/day) is not significantly changed when the animals are used at an abnormally high experimental density. This latter condition does, however, lead to the production of large quantities of additional nitrogenous substances that give a positive reaction with ninhydrin.

Introduction

The amounts of nitrogen excreted by zooplankton have been measured by several workers. Harris (1959) used the method of Riley (1953) to estimate the copious quantities of ammonia produced by animals (mainly Acartia tonsa and A. clausi) collected from Long Island Sound; Beers (1964), in laboratory experiments with the chaetognath Sagitta hispida, estimated the excreted ammonia by the procedure of Kruse & Mellon (1952); and Corner, Cowey & Marshall (1965) determined the ammonia excreted by Calanus helgolandicus and C. finmarchicus, using a ninhydrin technique described by Moore & Stein (1954). The methods employed by Harris and by Beers are specific for ammonia: that used by Corner et al. estimates nitrogenous substances (e.g. amino acids) in addition to ammonia, but certain tests were made which seemed to exclude the possibility that these substances contributed significantly to the nitrogen excreted by the animals.

A formal description of Rosalina leei sp.nov. (Foraminifera) includes an account of the great morphological variation found among adult agamonts obtained over a period of 14 months from clone cultures. Variation in chamber number, direction of coiling, overall shape, the degree of inflation of the final chamber and suture characters are detailed.

A population of Cucumaria elongata (Düb & Kor.), found in muddy sand off the Northumberland coast, has been sampled from 1961 to 1964. Densities of more than 20 per m were common.

Cucumaria is a suspension feeder, and uses its tentacles to trap suspended paniculate matter. In the absence of mucous glands or cilia on the tentacles, suspended matter is held fast in a covering of mucus which is produced by glands in the pharynx and oesophagus. Each time the tentacles are introduced into the pharangeal lumen in the course of feeding, they pick up a fresh complement of mucus.

The feeding behaviour is seasonal. During the early part of October the animals stop feeding, and remain dormant until late April/early May of the following year.

The results of monthly experiments to determine the oxygen consumption, percentage of total lipid and the volume/dry-weight ratio, have led to the conclusion that during the winter months Cucumaria hibernates.

The effect of temperature on the feeding behaviour is discussed.

Regular quantitative sampling has shown that Cucumaria is slow growing, and over the area surveyed, four different age-groups were found. These have been designated groups I, A, B and C. Group I was estimated to be 2 years old; group A, 6 six years; group B, 8 years; and group C, 10 years old.

Although active sperm and apparently mature eggs were found in specimens collected as far back as 1962, there is no evidence to suggest that any of the age-groups has reproduced.

Three species of copepods—Calanus finmarchicus (Gunnerus), C. helgolandicus (Claus) and C. hyperboreus (Krcyer)—can be easily and consistently differentiated by starch-gel electrophoresis of a number of their enzymes. The techniques used allow the study of individual variation in natural populations of small invertebrates, some of the variation being readily equated with known genetically based protein polymorphisms in man and other species. C. finmarchicus and C. helgolandicus have 15 enzyme zones in common and differ by 24-28 zones. By the rationale of molecular biology it can be suggested that these two forms differ in two-thirds of the structural genes. The results support the morpho-logical studies by Rees (1949) and Matthews (1966b) and the chromosomal studies by Harding (1963). Hence it is clear that the ‘finmarchicus-helgolandicus’ problem is solved: C. finmarchicus and C. helgolandicus are distinct species. The potentials and problems of biochemical systematics are discussed with particular reference to marine biology.

INTRODUCTION

Electrophoretic techniques have contributed to the solution of many taxonomic problems—for example, the monophyletic origin of ratite birds (Sibley, 1960), the discovery of a sibling species of sea-cucumber (Manwell & Baker, 1963 a; Manwell, 1966a), the status of species and populations of pheasants (Baker, 1965; Baker, Manwell, Labisky & Harper, 1966), the union of the orang-utan, chimpanzee, gorilla and man into one family, the Pongidae (Tashian, 1965), and the recognition of hybridization in lizards (Dessauer, Fox & Pough, 1962) and fishes (Manwell, Baker & Childers, 1963).

The amino-acid composition of Balanus balanoides (L.) and B. balanus (L.) da Costa eggs during their development has been investigated. Protein accounts for 70–80% of the dry matter. The amino-acid composition of the eggs is similar to that reported for Calanus finmarchicus, for which reliable information is available. Loss of all amino acids takes place during development, but the relative amounts of glycine and alanine increase in the late stages. The rates of loss are far greater in B. balanus, where the eggs themselves develop more rapidly. In B. balanoides there is a distinct ‘ arrest’ in the rate of loss of amino acids at the H-stage; this is coincident with a similar arrest in the loss of other metabolites and in development. Loss of nitrogen from the eggs has been measured directly and the results compared with the values calculated from the analyses. In the early stages the agreement is good if allowance is made for the difference in temperature between the elution experiments and the natural environment.

Data have already been presented (Barnes, 1965; Dawson & Barnes, 1966) on the major biochemical constituents of the eggs of two common cirripedes, Balanus balanoides and B. balanus, and on changes in these constituents during development. It has been shown that protein nitrogen is lost throughout development and that the rate of this loss is greatest during the early stages; also that nitrogen utilization relative to that of carbohydrate is greater in B. balanus. The more rapid development of the eggs of the latter species gives rise to a greater rate at which all substrates are utilized, but the proportions disappearing—relative to the initial quantities—are not widely different; rather more is lost in the species that develops more rapidly.

Spirula spirula (L.) when freshly caught was found to be close to neutral buoyancy. The pressure of gas within the chambers of the shell was always less than atmospheric, being very low in the newest chamber of a growing animal and rising to a value a little below atmospheric in the older chambers. A chamber which was being formed was completely full of liquid. The only connexion between the liquid in a chamber and the living siphuncle is through a small permeable region of the siphuncular wall which lies at the top of a newly formed chamber. These results support the hypothesis that Spirula, Nautilus and Sepia all regulate their buoyancy in the same way. The shell is sufficiently strong to withstand the hydrostatic pressure of the sea at the depths at which the animal lives.

The work of Colebrook & Robinson (1965) has shown that there are three groups of seasonal cycle in production in the north-east Atlantic. There are three ‘races’ of herring in the same area, spawning in autumn, winter and spring. Taking the dates of spawning of each ‘race’ and the date by which the larvae must have food, a connexion can be made between the herring race and the production cycle in the area in which it lives. It is assumed that the date of spawning is fixed and does not vary with environmental conditions. Once the connexion between herring race and production cycle is made, certain comparisons can be made between races in growth rate, reproductive capacity and in the variability of recruitment. It was tentatively concluded that the magnitude of the year-class in the three north-east Atlantic races must be determined before metamorphosis. After metamorphosis, herring live on the beaches where the production cycle must have quite a different character.

Introduction

Herring populations have been grouped as spring and autumn spawners ever since they have been examined scientifically. Autumn spawners have been further subdivided into early autumn (or summer) and late autumn (or winter) spawners (Johansen 1924). Since the discovery of sharp differences in fecundity and egg size between early and late autumn spav/ners (Polder & Zijlstra, 1959), the distinction between them has acquired the same status as that between autumn spawners and spring spawners. However, there are very marked differences between all three groups, and to relate them to then-calendar times of spawning it is proposed to name then ‘ autumn’ (formerly early autumn), ‘winter’ (formerly late autumn) and ‘spring’ spawners.

The inability of Lima Mans Gmelin to enclose the soft tissues of the body within the shell is correlated with the development of other defensive adaptations.

L, Mans can automize entire pallial tentacles or parts of tentacles which subsequently secrete a viscous mucus distasteful to potential predators. Autotomy takes place at transverse septa along the length of the tentacles and mucus is secreted by epidermal gland cells.

The transverse septa of the tentacles also regulate the hydrostatic pressure of blood within the tentacles and permit the performance of complex locomotory movements. It is suggested that the septa were originally developed to serve this locomotory function and, secondarily, function as planes of weakness at which autotomy may take place.

L. Mans builds protective nests. The nests are constructed by burrowing into a gravel substratum and consolidating the walls of the burrow with byssal threads. When disturbed in the nest L. Mans performs locomotory movements which lead to enlargement of the nest. If the nest is broken the locomotory activities result in free swimming followed by attempts to burrow into the substratum to form a new nest. It is unlikely that L. Mans swims freely in nature except when displaced from the nest.

Introduction

Most bivalve molluscs react to unfavourable stimuli by retracting the soft parts of the body within the shell valves and contracting the adductor muscles to oppose the valve margins. In Lima hians Gmelin the mantle margin, even with its numerous long tentacles fully retracted, cannot be accommodated within the shell valves. In this paper the inability of L. hians to retract the soft parts within the valves is correlated with two types of defensive behaviour: (i) the secretion of mucus by the tentacles of the mantle margin and the autotomy of these tentacles, and (ii) the interrelated activities of swimming and nest-building.

A description is given of a filamentous red alga which was found growing within a sponge collected from the sublittoral off Santander, Spain. The plant appears to be closely related to Acrochaetium spiculiphilum Dawson. A survey is given of the specific characters available for the typification of the known partially and completely endozoic Acrochaetium species, and some suggestions made on the more important lines of study.

Introduction

During the summer of 1957 some specimens of the keratinous sponge Haliclona were collected from the sublittoral off Santander, Spain, by Mr G. R. Forster. Certain of the specimens bore extensive areas of red, and on preliminary examination this colour was found to be due to the filaments of a red alga showing an extensive ramifying growth within the skeleton of the sponge. The drawings and cell measurements to be reported were made from the plant material by A. D. B. soon after its collection. This information has been retained pending a more comprehensive study of endophytic and endozoic red algae. Work is now in progress on these lines (mainly by E. B. W.), and a re-examination of the Santander material has enabled us to make a critical study of the data available for a precise typification of plants of this habit. Further, since the association of endozoic filamentous red algae with sponges appears to be of rare occurrence, any examples need to be fully described.

Description of Plant

The cells were of variable shape and size, and contained much-dissected parietal chromatophores (Fig. 1 a). Individual filaments tended to be closely packed together within the host (Fig. 1 b), and there was no extensive growth of erect filaments outside of the host material.

Ectocarpus distortus and E. landsburgii are shown to be conspecific and to constitute free-living ecads of E. fasciculatus. It is therefore recommended that the two should no longer be regarded as true species although it is pointed out that the specific epithet E. distortus may have priority over E. fasciculatus. If so, the entire complex, provisionally retained as E. fasciculatus, may have to be known as E. distortus. Meanwhile it is recommended that the list of British Ectocarpus spp. be reduced to two, namely E. fasciculatus and E. siliculosus.