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.

A new scyphomedusan is described which was collected on a dive by U.S. research submersible Deepstar 4000 at 723 m. in the San Diego Trough. The specimen was incomplete. It is characterized by a gastro-vascular canal system in the form of a uniform network, and by the unusual form of its gonads. Its systematic position is uncertain. The medusa is named Deepstaria enigmatica gen.nov., sp.nov.

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.

Larvae of the oyster (Ostrea edulis L.), when released, can live for several days without food, and can grow to full size when subsequently fed. Energy is supplied by protein, carbohydrate and lipid of the larval body, all of which decrease during starvation. The measured decreases are sufficient to account for the energy expended as indicated by oxygen consumption.

Nitrogen retained and nitrogen excreted by Calanus finmarchicus (Gunnerus) have been measured at all stages of development from egg to adult; and the percentage of food digested by adult females grazing algal diets has been estimated by two separate methods. The data have been used to calculate gross efficiency of growth by the young stages as well as that of egg-production by the adult female. They show that during a life-span of approximately ten weeks the animal uses 24% of the nitrogen it captures as food in order to build new tissue and produce eggs; the remaining larger fraction is lost as faecal pellets, moults and excreted end-products of metabolism.

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.

The larva of the dolichopodid fly Aphrosylus celtiber Haliday is an omnivorous carnivore in the intertidal zone. It pupates in an air-filled cocoon of debris and a secretion of the labial glands. The pupa has plastron-bearing spiracular gills that have been evolved from respiratory horns similar to those of recent terrestrial Dolichopodidae.

Although the spiracular gills are pupal structures, they are the chief respiratory organs of the young adult, i.e. the pharate adult, before it emerges from the cocoon. At the pupal-adult apolysis the layer of epidermis that secreted the gill wall and the layer that secreted the spiracular atrium are left behind in the lumen of the gill, together with blood, as the body wall epidermis retracts away from the pupal cuticle. A thin sheet of cuticle, the basal membrane, is secreted across the opening into the gill lumen at this time. The epidermis and blood in the gill lumen are thus completely isolated from the haemocoele of the living animal by the basal membrane, a layer of moulting fluid, and the adult cuticle. The tissue contained in the respiratory horns of terrestrial Dolichopodidae is isolated in a precisely similar manner.

The tissue isolated in the lumen of the gill of Aphrosylus does not degenerate until after the pupal-adult ecdysis. It seems to be discarded because, on balance, its loss is less damaging than the cost that would be incurred in other ways by its absorption or retraction into the body of the adult. For instance, in order to absorb the tissue in such long appendages, or to retract all of the epidermis from within them, would necessarily prolong the moulting period, a period when the insect is particularly vulnerable.

A sensitive, specific and precise method for the determination of ammonia in sea water is presented. The method depends upon the oxidation of ammonia by chloramine-T and subsequent coupling with phenol to produce indophenol blue in an n-hexanol extract. Molar absorption coefficient ca 84,000. Values of ammonia measured in samples from the English Channel are given and the effect of freezing on samples for ammonia analysis is discussed.

A new species of Breviraja is described from a pair of fish caught by line at nearly 2500 m depth in the Bay of Biscay. Distinctive characters include: the sparse distribution of denticles and spines, small number of teeth, position and size of the orbits, and very pale dorsal surface.

Two unusual specimens of Raja richardsoni Garrick from the N. Biscay area lacked part of the snout, apparently because it had been bitten off.

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.

The conchocelis-phase of Porphyra tenera Kjellman has been grown in in vitro culture, and subjected to a variety of daylength treatments.

Details of the culture apparatus designed for these treatments are given, and quantitative techniques, which have been devised for estimating the growth and reproduction of the alga, are described and discussed.

Growth was found to be directly proportional to daylength within the range 8–16 h, but abundant sporangia were only formed in daylengths of 10 h or less. The interruption of a 16 h dark period by 1 h of light completely inhibited the production of sporangia, but exposure to 8 short-day cycles, followed by long days, induced the formation of as many sporangia as were found after 25 short days. These results are discussed with reference to the photoperiodic responses of flowering plants.

A tagging investigation on the ormer (Haliotis tuberculata L.) has been carried out for the Guernsey States Sea Fisheries Committee. Cementing plastic discs to the shell has proved a satisfactory technique since substantial numbers of 40—50% were recovered after 1 and 2 years in the open sea off the west coast of Guernsey. From the increase in shell size of the recovered specimens the mean growth rate has been shown to be about 15 mm of shell length per year up to a shell size of 50 mm, and thereafter decreasing until at 100 mm length growth is negligible. The growth parameters K and L∞ have been calculated. Annual rings were frequently, though not invariably, found on the shell. From the frequencies of the shell-ring lengths in the smaller ormers estimates of the shell size reached 1 and 2 years after settlement have been made. A single annual ring was also found with the majority of the larger shells (> 50 mm), though when growth did not exceed 4 mm in a year the rings were not included owing to the difficulty of separating annual rings from possible disturbance rings caused by the process of tagging. The position of the annual ring varied, being closer to the outer edge of the shell with increasing size. Measurements of the length increase from one annual ring to the next indicated rates of growth closely comparable to those obtained from tagging measurements. Damage to the shells by the boring sponge Cliona lobata Hancock is very widespread, particularly in the larger ormers living below the tide marks.

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).

Spirorbis vitreus (Fab.), an arctic form, seems to be absent from Wales and most of England, but is generally abundant off the west coast of Scotland and also occurs in certain localities off Ireland, the Isle of Man, Cornwall and Brittany (which is probably its southern limit in Europe). Its range thus extends farthest down our western coasts, a distribution which is characteristic of various other northern and southern forms that are near the limits of their geographical ranges. Such species presumably benefit from the equable temperatures, adjoining deep water, and this winter-breeding species of Spirorbis also needs freedom from abrasion.

The tubes of juvenile S. vitreus are very different from those of adults. The distribution of uncini on the abdomen shows a remarkable bilateral asymmetry, as in S. spirillum.

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.

Various aspects have been studied of the relationship between the entocommensal nemertean Malacobdella grossa [O.F. Müller, 1776] and its host on the Yorkshire coast, the lamellibranch Zirfaea crispata L. Larger host populations clearly show both a higher overall percentage infection and greater numbers of multiple infections. Larger hosts tend to harbour larger Malacobdella; allied with this fact is the conclusion that the older the host population the more restricted is the availability of potential hosts for future infections.

The larva of the fly Canace nasica Haliday feeds on Enteromorpha in the intertidal zone. Its pupae, like those of a number of other intertidal flies, have plastron-bearing spiracular gills. The gills are unlike those of any other known Diptera in that they are modified spiracles: those of other flies are modifications of the body wall adjoining the spiracle, or of both the body wall and the spiracle. Although the spiracular gills are pupal structures, they are the respiratory organs of the adult before it emerges from the puparium.

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.