Preliminary examination of marine meiofauna from the Plymouth area, especially on mesopsammic representatives, resulted in the finding of several typically interstitial Mollusca. Among them, Caecum glabrum, Hedylopsis spiculifera, and Philinoglossa praelongata were recorded live for the first time in the area. This is also the first record of Ph. praelongata outside the Mediterranean Sea.

During a short stay at the Marine Biological Association Laboratory some preliminary studies on meiofauna were made. To obtain information especially about the interstitial fauna of marine sand, three typical samples of coarse sediment from different positions were examined.

Sample A: Plymouth Sound, Outer Cawsand Bay, Queens Ground, 50°20' 03“ N, 4° 10' 27” W; ca. 6 fathoms (=11 m); coarse sand, about 6 1 examined (14 September 1982).

Sample B: Plymouth Sound, southwest of Drake Island, 50° 21' 06“ N, 4° 09' 50” W; ca. 7 fathoms (= 13 m); coarse shell-sand, about 1 1 examined (15 September 1982).

Sample C: outer Plymouth Sound, 50° 18' 51“ N, 4° 10' 30” W; ca. 12 fathoms (– 22 m); fine gravel, about 1 1 examined (15 September 1982).

In this contribution only the gastropods are dealt with; other meiofauna will be treated ina later communication. The sole previous report of mesopsammic fauna from the Plymouth area is that of Spooner (1959). He examined two samples, one of which (Plymouth Sound) was taken fairlyclose to the above sample A, about 18“ more to the West at 4–5–5–5 fathoms (8–10 m; G. R. Forster, personal communication).

Sea trials, using baited pots (inkwell and French barrel) and nets (tangle and gill), were conducted for the spider crab Maia squinado off the west coast of Ireland from November 1978 to July 1980. A series of laboratory pot trials using inkwell pots were performed. Diving observations were made on the fishing grounds.

Catch per unit effort rose to a summer peak and decreased in autumn. There was no difference in size composition or sex ratio of the catch between the pots and nets. Mature males predominated in the catch with the highest male:female (M:F) ratios recorded in summer. Immatures were virtually absent from the catch. Segregation on the basis of sex and maturity appears to occur in summer. Mature males were found at about 10 m, in sandy areas with rocky outcrops. Mature females occurred at about 5 m, on a sand and shell gravel bottom with rock and weed (notably Laminaria). Immatures were rare and occurred just below the intertidal. The M:F ratio was lowest during the periods of the onshore and offshore migrations. Berried females were recorded from March to September with one brood produced each year.

Laboratory pot trials showed increased aggression among spider crabs in the presence of baited pots. Males drove other males away from pots and divided their time between agonistic encounters and searching. Females were not driven away and did not engage in aggressive encounters. This behaviour, and the observation that large males could reach the bait through the pot bars, possibly explains the absence of larger and smaller males from the pots.

Ten species of deep-water Pycnogonida are recorded, mainly from the north-eastern Atlantic Basin. Of particular interest are Ascorhynchus abyssi Sars (new to the British Isles), Colossendeis arcuata A. Milne Edwards (northernmost record in European waters), C. bicinc0ta Schimkewitsch (third Atlantic record, depth range increased), C. macerrima Wilson (new records from the English Channel), Nymphon laterospinum Stock (new to the Indian Ocean), Pallenopsis (Bathypallenopsis) oscitans (Hoek) (new to the English Channel and bathymetrical range extension), P. (B.) tritonis Hoek (extension of depth range), P. (B.) tydemani caraibica Stock (second European record, now found at the entrance of the English Channel), and Anoplodactylus arnaudae Stock (range extended to the Rockall Trench).

The capture of specimens of Crenilabrus bailloni Valenciennes, 1839 from Galway Bay, Republic of Ireland, and off the coast of Jersey, Channel Islands is reported. Occurrences of this species in northern European waters are discussed. It is concluded that this wrasse is a Lusitanian element in the northern fauna, and suggested that it may be more common in the fauna than records indicate due to its inhabiting a little collected habitat and on account of its similarity to the common corkwing wrasse C. melops (Linnaeus, 1758). Methods of distinguishing the two species are given.

Homogenates of pyloric caeca, gonads, spermatozoa and eggs from the starfish Asterias rubens were fractionated by gel filtration chromatography.

It appeared that a glycolipoprotein fraction, present in oocytes and gonads of female animals, is absent in spermatozoa and gonads of male animals.

The possible role in vitellogenesis of this fraction and of a more omnipresent one is discussed.

The reproductive cycles of four widely separated Modiolus modiolus populations from W. Sweden, W. and N. Norway, and Northern Ireland were examined in relation to their contrasting temperature regimes. Reproductive condition was analysed on the basis of the degree of development and numerical density of the gametes, and on size-frequency distributions of oocytes.

All the Scandinavian populations had well defined spawnings, those of W. Sweden and W. Norway occurring in June and followed by a period of redevelopment and further gamete release. The N. Norway population spawned in July and subsequent redevelopment was not accompanied by further spawnings. Both Norwegian populations overwintered in a relatively ripe condition, but that from W. Sweden spent the winter in a low state of reproductive development. The N. Ireland population contrasted with the others in being continuously ripe and having no overt spawning, but rather a slow, constant release of gametes throughout the year.

These differences are assessed in terms of the effects of the local temperature regimes on the interacting processes of gametogenesis and spawning. It is concluded that seasonal variability in temperature plays a major role in determining the extent and duration of gametogenesis, whilst spawning is more dependent upon the attainment of a limited range of minimum temperatures. The northern limit of M. modiolus is therefore more likely to be determined by failure of conditions suitable for spawning and larval development than by a failure of gametogenesis.

The free living eulimid gastropod Melanella alba Bowdich, 1822 is a temporary ectoparasite on echinoderms and, in Kilkerrin Bay on the west coast of Ireland, this species is found exclusively associated with the holothuroid Neopentadactyla mixta (Östergren), 1898. Melanella utilizes a highly specialized acrembolic proboscis to penetrate the integument and ingest the internal tissues of this holothuroid. That portion of the proboscis which penetrates integument bears a highly developed secretory epithelium composed of granular and goblet secretory cells. As the proboscis is unfolded into the host's integument by a combination of increased hydrostatic pressure and muscular movements, secretory material is released from this epithelium and appears to bring about a rapid loosening of the connective tissue elements of the host. The possible mechanism by which the integumental connective tissue is altered to allow unfolding of the proboscis into the coelomic cavity of the host is discussed.

Atelecyclus buries itself by digging backwards into the sand, sometimes until only the antennae protrude above the sand. In this position it is difficult for the animal to maintain an adequate respiratory current through the branchial chambers by pumping water in the normal direction.

Studies of the ventilatory behaviour of Atelecyclus have shown that, when on the surface of the sand, water flows through the branchial chambers as in most other crabs i.e. water enters the chambers at the base of the limbs and the exhalant water leaves anteriorly. This direction of flow is also maintained when the crabs are only partially buried but when more deeply buried, the direction of water flow is reversed by the reversal of the direction of beat of the scaphognathites and water is drawn down the antennal tube and leaves the branchial chambers at the base of the limbs.

Inactive Atelecyclus show a well-defined rhythm of pumping in which regular periods of active pumping alternate with periods during which the scaphognathites stop beating and ventilation of the branchial chambers ceases. The rhythm of ventilation is regular but the duration of the ventilatory pauses (apnoea) may vary considerably between animals.

During pausing, the activity of the scaphognathites and of the heart are closely synchronized. The cessation of scaphognathite activity is accompanied by a period of cardiac arrest, although single heart beats may sometimes occur during a pause.

As in many decapods, the Po of the post-branchial blood was high (Pa, o = 92 torr, Pv, O = 21 torr) but during a pause P, o gradually declined.

Material from Loch Fyne referable to Monoculodes gibbosus Chevreux (Oedicerotidae) has been discovered in the Reference Collection at Millport originally labelled by David Robertson as M. stimpsoni Bate. This is the first British record of this little known species. A detailed redescription is provided and comparison made with French material (including the holotype). A revised key to the British species is presented.

Samples collected regularly from the intake screens of power stations between July 1972 and June 1977 demonstrate that the Gadidae is the most abundant and diverse teleost family in the inner Bristol Channel and Severn Estuary. The first records for the Severn Estuary of two cold water species, northern rockling and Norway pout, which were present in appreciable numbers, may be related to the effects of the changes that commenced in south-western English waters during the 1960s. Maximum numbers of the five most abundant gadoids were attained in different years, with the greatest catches being recorded for whiting and poor cod in 1975/6, bib and pollack in 1974/5 and northern rockling in 1976/7. Peak abundance in the middle estuary was reached by whiting, bib, poor cod and pollack in the autumn and by northern rockling in the winter or early spring. The 0 + age class of these species, which was always by far the most predominant category, showed increases in mean length during their relatively short stay in the estuary. Movement out of the shallows of the inner Severn Estuary by whiting and also apparently by some other gadoids occurred when salinities fell below 10‰. The size of poor cod and pollack in the autumn was not as great in 1974 as in 1975 and 1976, presumably reflecting the effect on growth of lower summer temperatures in the first of these years. Poor cod was represented by five age classes and attained at the end of the first to fifth years of life standard lengths of approximately 80 mm (≡4.8 g), 110 mm (≡11.7g), 140 mm (≡23.0 g), 170 mm (≡39.6 g) and 210 mm (≡71.6 g) respectively.

Populations of Idotea pelagica and Idotea granulosa were studied monthly at Carnsore Point, County Wexford, from July 1978 to October 1979. The density of I. pelagica in mussel beds varied between 26 and 180/100 cm, reaching a peak in June. Numbers of I. granulosa in samples of Gigartina stellata fluctuated from month to month and averaged 200/100 g dry weight of algae. Peak densities were recorded in September of both years. Both species exhibited continuous growth, and breeding occurred throughout the year but with a main breeding period starting in winter. I. pelagica grew more rapidly and had an extensive breeding period lasting from December to August with two generations, some members of both generations producing second broods. For I. granulosa, the main breeding period was January to April, after which most adults died. Some of their offspring reached maturity in late summer giving rise to a lesser breeding peak in late summer and autumn but most did not mature until winter. Summer breeders of both species were smaller than those breeding in winter. The breeding cycles are compared with those of other populations in Britain and the Baltic and the possible reasons for the differences discussed.

Mussels, Mytilus edulis L. grow on the shore and are cultured on ropes in Killary Harbour, a fjordic inlet on the Irish west coast. The food resource available to cultured mussels differs from that available to wild mussels on the shore. Although phytoplankton densities as estimated from chlorophyll a concentrations are similar, the shore environment in the inner part of the inlet is characterized by high mean POC concentrations. This is because of the presence of variable amounts ofallochthonous detrital carbon.

The annual cycles of flesh weight and ash content of wild and cultivated mussels were followed over two years. These cycles were related to the reproductive cycle observed by taking histological samples of mussel gonad, by plankton sampling for larvae and by monitoring larval settlement. Shell growth was measured in wild mussels by reading seasonal growth patterns on sectioned shells and in cultured mussels by following progress of the modal shell length of cohorts on ropes.

Wild mussels have a partial spawning in early spring and spawn completely in the summer. Cultured mussels spawn twice during the summer, in the year following settlement. Growth rate of wild mussels decreases with increasing aerial exposure. The fastest growing mussels, at o % exposure, take about 6 years to attain the length attained by the mode of the cultured mussels after 18 months, when they are harvested.

We conclude that wild mussels utilize a mix of phytoplankton and detritus as food during the summer and that large wild mussels can use detritus during the autumn and early winter for an increase in flesh weight and gametogenesis.

Aora spinicornis Afonso is recorded for the first time from the British Isles. Two species of Aora, A. gracilis (Bate) and A. spinicornis Afonso are now known from these waters. A. typica Krøyer, long considered a British and Irish species, is actually known only from the Southern Hemisphere. Figures and diagnoses of both species are provided together with a key to their identification.

Introduction

Lincoln (1979) records one species of Aora Kreyer from British and Irish waters. Due to an oversight (Lincoln, personal communication) he overlooked the paper by Myers (1973) (although listed in the bibliography) and attributed the single species to A. typica Krøyer, a species actually known only from the Southern Ocean between 20° S and 50° S (see Myers & Moore, 1983 which also includes a key to the world species). Two species of Aora are now known from the British Isles: A gracilis (Bate) which is widely distributed, and A. spinicornis Afonso, recently discovered in Lough Hyne, Co. Cork, and herein reported for the first time from these waters. This latter species has a Lusitanian distribution (Azores, Canaries, Mediterranean) and may occur in south-western England and Wales, but has been confused previously with A.gracilis (Bate). Both species have been described and figured by Myers (1973, 1982) and do not require further detailed analysis. However, since both species are now known to occur in these waters and are not both treated by Lincoln's widely used monograph, the two species are figured here as entire specimens (for details of appendages including mouthparts see Myers, 1982) and briefly diagnosed, and a key is provided to facilitate their identification by British and Irish workers.

The annual cycles of the Abra tennis populations in the Plym Estuary and the Fleet (Dorset) were studied from March 1980 to June 1982. In the Plym Estuary the highest numbers occurred in autumn following juvenile recruitment and the lowest numbers were recorded in mid-summer. In the Fleet such an annual cycle in numbers was not apparent since juvenile recruitment in 1980 was very high but in 1981 it was very low. The recruitment failure in 1981 may have resulted, at least in part, from the heavy summer infection of A. tenuis by digenean parasites that destroy the gonads of the host, thereby reducing the population fecundity.

A. tenuis spawns in July and August: the mature egg has a diameter of 140 μm and is enclosed in a sticky gelatinous envelope. Females produce 450–1800 eggs which, when fertilized, are laid in a mass within the sediment and, following a direct development, the juveniles hatch as miniature adults after 2–3 weeks. This non-pelagic, lecithotrophic development is interpreted as being a means of ensuring the maintenance of populations within restricted estuarine habitats. Data suggest A. tenuis lives for 1 or 2 years and that the species is monotelic.

An examination of the proportions of pedal disc colour and isozyme phenotypes, in samples of Actinia equina L. collected from around Britain, has shown that individuals which are heterozygous for a gene complex involved in morph determination occupy a habitat intermediate in position to those occupied by the two homozygotes. It is concluded that A. equina may best be considered as comprising three morphs, rather than two as had been distinguished previously.

As the abundance of anemones in samples displaying a particular pedal disc colour phenotype decreases, the proportion of these individuals which possess atypical combinations of colour and hexokinase-i phenotypes increases. This result is interpreted as indicating that individuals are subject to differential selection in different habitats, dependent upon their genotypes at hexokinase-i, or those at some other tightly linked locus.

Introduction

Our recent work on Actinia equina L. has revealed the existence of two morphs amongst anemones collected from British coasts, having column coloration ranging from red to brown (Quicke, Donoghue & Brace, 1983). One morph displays pedal disc colour (coloration) (PDC) ranging from red to pink (R), and occurs in the upper part of the intertidal range of this species, where it is commonly found firmly attached to vertical rock faces. The other has a grey (G) or green (H) pedal disc, which may sometimes display contrasting red or orange radial lines (L); these colour phenotypes will be collectively referred to as GHL. This latter morph occurs predominantly at a lower tidal level, where it usually occurs on horizontal surfaces to which it adheres relatively weakly.

The distributions of Asterina gibbosa and A. phylactica in the Lough Ine area are described and compared. The species are shown to have different horizontal distributions with respect to wave exposure. Clear ecological separation is demonstrated where their distributions overlap as a result of micro-habitat preferences.

Oxygen consumption was measured in squid (Illex illecebrosus) ranging from 42·7 to 443·0 g. Ambient temperature increased from 8·3 °C to 18·2 °C during the experimental period. Resting rates were calculated by correcting for the percentage of time not spent in the resting posture. A 100 g squid resting at 13 °C has a predicted oxygen consumption of 31·3 ml/h, while a continuously swimming squid has an oxygen consumption of 125·0 ml/h. Oxygen consumption is almost directly proportional to body size. A 10° increase in environmental temperature would increase oxygen consumption for a squid of given mass by 6·7 times.

A new species of a monogenean Isancistrum subulatae (Gyrodactylidae) has been discovered on the arms and tentacles of the cephalopod mollusc Alloteuthis subulata at Plymouth and I. loliginis, on the gills of the same host, has been re-discovered for the first time since its original description in 1912. I. subulatae, like other gyrodactylids, is viviparous, and has been shown by experiments to transfer to new hosts by contagion. In nature such transfers probably take place during copulation of the hosts and since the parasite may occur in numbers of several thousands per host, it may thereby constitute a venereal disease.

The shapes and dimensions of the statocysts of cephalopods have been measured and compared with the semi-circular canals of vertebrates. The cavities grow much more slowly than the body as a whole, but there are knobs, anticristae, which restrict the cavity, and these grow relatively faster. This ensures that the flow of endolymph across the cupulae remains small. Where the liquid is constrained within canals the radius of curvature of the whole canal, R, is similar to that of fishes, whereas its internal radius, r, is twice as large in non-buoyant and four times as large in deep-sea buoyant cephalopods as in fishes of similar size. As in fishes the restriction is greatest in the horizontal plane, providing for operation at higher frequencies in turning about the yaw axis.

The statocysts of seven species of Loligo all have similar proportions. The largest individuals of 16 genera of non-buoyant squids also have these same relative dimensions. The statocyst of Sepia is more like that of non-buoyant than of other buoyant cephalopods but yet differs significantly from that of Loligo at all sizes. On the other hand 21 genera of squids known to be neutrally buoyant are very different. Their statocysts are often larger than in the non-buoyant forms and there is less restriction of the cavity by anticristae. The greater flow of endolymph acting across the cupulae presumably provides greater sensitivity at the lower frequencies of turning of these deep-sea animals.

The data suggest that the cristae of the cephalopod statocyst may operate in the frequency band where they act as angular accelerometers whereas the vertebrate semi-circular canals operate at higher frequencies as angular velocity meters.

In Carcinus maenas haemolymph, zinc is almost entirely bound to the respiratory pigment, which is the copper-protein haemocyanin (Hc). Zinc ions are loosely bound, as indicated by the low value of the association constant (k = 1.7 × 105 M-1 at pH = 8.0). The number of binding sites N is equal to 4 per minimal functional subunit (75000 Dalton). No co-operativity has been found between the different metal sites. Data reported in this paper support the hypothesis that haemocyanin can act as metal carrier in the haemolymph of C. maenas.