1. In regard to relative abdomen-breadth and relative carapace-breadth, the common shore-crab Carcinus maenas in both sexes exhibits a continuous change of proportions throughout life, from small animals of 2 mm. carapace-length to the largest obtainable (over 50 mm. carapace-length).

2. The parts measured exhibit constant differential growth-ratios (growth-coefficients) relative to carapace-length taken as standard, over long periods of the life-history.

3. The approximate growth-coefficients are as follows, relative to carapace-length:

Carapace-breadth, 1·06. This appears to be constant throughout the range of size measured, with a possible decline to nearly unity at large sizes.

Abdomen-breadth.

Crabs unsexable externally (2–6 mm. carapace-length), 1·26.

Females: early phase, 1·26; late phase, 1·42.

Males: early phase, 1·07; late phase, 0·94.

The early phase begins as soon as the sexes can be distinguished. The onset of the late phase may be presumed to be correlated with sexual maturity. In females it occurs certainly between 17 and 20 mm. carapace-length, in males between 14 and 29 mm.

4. There are indications of seasonal and local differences in relative abdomen size.

5. Feeding crabs of 9 to 22 mm. carapace-length solely on fresh ox-thyroid or fresh ox-pituitary for periods up to a year produces no change in growth-rate or in secondary sexual characters as against controls fed on fresh fish.

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.

The composition of meiobenthic and macrobenthic communities between different intertidal reef-flat pools on Rocas Atoll (South Atlantic) was compared, and related to properties of the carbonate sediments and patterns of reef growth. Both univariate and multivariate statistical analyses showed that the reef height and size influenced the properties of the reef-derived sediments and were correlated with the composition and abundance of the benthic fauna in the intertidal pools. The temperature and the salinity between Rocas tidal flat reef pools did not vary significantly, despite the differences in size, exposure degree and elevation, suggesting that percolation through the porous lime body of the reef and/or the connection between the tidal pools and seawater by blowholes have a significant effect on the tidal pools. The major asymmetry in the reef topography of Rocas Atoll was observed between the leeward and windward reefs, which paralleled the largest changes in sediment properties and faunal structure inside intertidal reef pools. Sediments from the tidal pools located in the windward side of the atoll were significantly finer, the organic content higher and the benthic fauna more abundant and diverse. The results of this study suggest that significant changes in the sediment properties and benthic community structure between the intertidal reef-flat pools of Rocas Atoll may be primarily conditioned by different patterns in reef growth.

During my researches on the vertical and seasonal distribution of young fishes I soon noticed that occasionally a specimen was found to which a Caligid copepod in an early chalimus stage was attached. As every fish caught was examined under the lens while being measured, I kept a look out for these young stages of the parasites and all occurrences were recorded. The results of this examination are given in Table I which shows also the lengths in millimetres of all the fish thus parasitised found in the collections made during 1925 and 1926 (see 1, 2, 3 and 4).

The osmotic pressure and sodium concentration of the coelomic fluid of two species of httoral centipede have been measured and compared with those of a terrestrial one. A similar value of about 45 % sea water was obtained for all three species. Weight changes and longevity experiments in normal and diluted sea water suggest that littoral species are less permeable than terrestrial ones and it is suggested that the enlarged salivary glands of littoral species could be the site of salt secretion. A comparison is drawn with teleost and other examples whose body fluids are hypotonic to their environment.

We investigated the occurrence and seasonal variation of the biomass of rotifers, tintinnids, the heterotrophic dinoflagellate Gyrodinium fusus and copepod nauplii in the Bahía Blanca Estuary (38°42′S61°50 ′W), Argentina, during an annual cycle. The rotifers fauna comprised three species, while the tintinnids were represented by sixteen species. The biomass of the rotifers fluctuated between 0.62 and 8.90 µgC l−1. The biomass of the tintinnids fluctuated between 0.13 and 9.37 µgC l−1, the biomass of the nauplii stages between 1.78 and 7.65 µgC l−1; while the biomass of G. fusus varied from 0.26 and 7.94 µgC l−1, these results are compared to estimates of microzooplankton in other regions. We analysed the presence of the different groups in relation to the environmental variables, based on point-biserial correlation. Salinity fluctuated between 25.14 and 36.64; temperature between 7.5 and 23.2°C, solar radiation between 0.9 and 30.8 MJ m−2d−1 and Secchi distance between 0.25 and 1.43 m. Rotifers were correlated positively with temperature, chlorophyll-a and Secchi depth and negatively with salinity. The tintinnids were positively correlated with salinity. Gyrodinium fusus was positively correlated with Secchi depth, and chlorophyll-a, and negatively with temperature and solar radiation. Nauplii stages were negatively correlated with chlorophyll-a. Based on the occurrence of the microzooplankters in relation to the physico-chemical variables, it was possible to establish two seasonal assemblages: (a) the co-occurrence of the rotifers and the heterotrophic dinoflagellate G. fusus during the winter–spring; and (b) the tintinnids and nauplii larvae during the summer. We conclude that, in this estuary, physico-chemical variables are the forcing factors that directly, or indirectly, influence the seasonal assemblages of the microzooplankton.

1. The period of time which the oyster larva requires to attain its respective developmental stages was measured and recorded in 0. virginica and 0. angulata.

2. The development in various concentrations of salinity was studied in the three species, 0. virginica, 0. angulata, and 0. edulis.

3. In optimum salinity, all the impregnated eggs undergo segmentation and further development; the rate of development is uniform and its progress speedy.

Four squid species from around Scotland and in the northern North Sea were examined for larval ascaridoid nematodes maturing in warm-blooded vertebrates. A larval contracaecinean (possibly Contracaecum osculatum) in Loligo forbesi, and Anisakis simplex L in L. forbesi, Alloteuthis media and Todaropsis eblanae are recorded, apparently for the first time. Neither of the inshore neritic myopsids L. forbesi and A. media appears to be an important host of Anisakis simplex L3. The oceanic oegopsid Todarodes sagittatus showed the highest A. simplex L3 burdens; whilst the general pattern of infection in this species was similar to that of teleost fish in the northern North Sea, the density of infection was lower. The possible significance of L3 in squid for the population dynamics of A. simplex is discussed. Larval ascaridoid nematodes in squid may have no public health significance in the U.K.

The effects of cell concentration on colony growth and feeding behaviour were investigated in the polymorphic marine bryozoan Celleporella hyalina (Bryozoa: Cheilostomata) under controlled, laboratory conditions. We compared the relative zooidal composition of colonies cultured on Rhodomonas baltica (Karsten) for seven weeks at 18°C. We observed the pharynx of active lophophores on sudden exposure to high cell concentrations, and recorded the length of feeding episodes and ingestion rates.

Colonies grew, reproduced and produced viable larvae at all levels of food supply, but performed optimally at 50–100 cells µl-1. Cell concentration influenced somatic parameters more than sexual, the latter being more closely associated with genotype. Relative somatic investment was greatest at 10 cells µl-1 and least at 50 cells µl-1. The frequency of ovicells containing larvae remained at about 74% irrespective of food supply. Basal male investment was greatest at 10 cell µl-1, frontal male investment at 50 cells µl-1, and female investment at 100 cells µl-1.

Cell ingestion rates of previously starved zooids increased as a function of cell concentration, with an inverse relationship between length of feeding episode and concentration. Food particles were drawn from below the lophophore by lateral cilia, ciliary reversal brought them over the mouth, and ingestion then resulted from a pharyngeal current. These results suggest that, on exposure to high cell concentrations, bryozoans may exhibit specific behaviour.

The use of stolons in competitive interactions between several species of bryozoans growing in Townsville Harbour, North Queensland is described. Stolonal growth resulted in overgrowth reversals and redirected growth in interactions between Schizoporella unicornis and Watersipora subtorquata. These results suggest that stolons may play an important role in bryozoan interactions

Convoluta roscoffensis (Graff) has long been known for its symbiosis with a green flagellate definitively described from French stock as Platymonas convolutae by Parke and Manton (Parke & Manton, 1967). Provasoli subsequently discovered a species of Prasinocladus in a culture isolated from C. roscoffensis, but concluded that it was a surface contaminant of the animal (Provasoli, Yamasu & Manton, 1968).

Populations of C. roscoffensis from Aberthaw, South Wales (Mettam, 1979), and eighteen sites on Guernsey have been studied. In most patches of the Aberthaw colony, and in two of the Guernsey sites, two algal symbionts have been found. One of the Guernsey, and one of the Aberthaw symbionts appear identical to Platymonas convolutae.

They can be distinguished at the ultrastructural level by the presence of canaliculi which penetrate the pyrenoid, and are lined with the double-layered plastid envelope. In both cases the second flagellate shows the nucleus-pyrenoid complex typical of the genus Prasinocladus, where the nucleus penetrates the pyrenoid, and a pair of thylakoid membranes separate the pyrenoid from the starch shell (Parke & Manton, 1965). Neither symbiont has been identified specifically.

It is also possible to distinguish the two symbionts in the living animals, since the cup-shaped pyrenoid of the Prasinocladus type is easily distinguished from the spherical condition in Platymonas using the light microscope. A mixed population of symbionts has never been found in an individual worm. For each patch of animals in a colony it was possible to establish the percentage of animals containing each symbiont. This ratio varies from patch to patch in the colony, but has remained remarkably constant within each patch over the six months it has been studied. The Prasinocladus type always predominates at Aberthaw, the Platymonas type being absent in places.

The podocyst is a cuticular patella-shaped stage in the life-cycle of certain scyphopolyps and has been described recently (Chapman, 1968) from the standpoint of anatomy, histochemistry and development. New material has come to hand necessitating a reassessment of the views concerning the formation of this deceptively simple structure.

Two new species of free-living marine nematodes of the genus Elzalia, Elzalia gerlachi sp. nov. and Elzalia striatitenuis sp. nov. from the Yellow Sea, China, are described and illustrated. Elzalia gerlachi sp. nov. is characterized by relatively large body length (1540–1740 μm in males; 1510–1780 μm in females), spicules 135–160 μm (3.33–3.90 anal body diameter) and complex gubernaculum. Elzalia striatitenuis sp. nov. is characterized by rather small body size (560–660 μm in males; 570–630 μm in females), short cephalic setae 2.5 μm long (21.4–31.3% of head diameter), spicules 65–85 μm (4.06–4.67 anal body diameter) and relatively simple gubernaculum. The two new species can be distinguished from other species of the genus by length and structure of spicules and gubernaculum. Pictorial and tabular keys to the genus are given.

Reproductive tactics displayed by the mole crab Emerita brasiliensis that inhabits Atlantic beaches of South America are reported. The analysis of external sexual characters and reproductive organs disclosed seven developmental forms: megalopae, neotenic males, early females, juveniles, males, females (ovigerous or not) and intersex individuals. Precocious acquisition of gonopores in females, production of spermatophores in neotenic males and presence of juveniles and intersex individuals are reported for the first time for this species. Sex ratios were biased towards male forms in summer, whereas the opposite trend was observed in autumn. The occurrence of different forms within a single population, coupled with a marked temporal variability in its abundance, suggest a high complexity in the sexual life cycle of the mole crab. This involves two different pathways: (a) short, where megalopae moult into neotenic (mature) males or early females; and (b) long, following a sequence of moults involving several stages (zoeas, megalopae, juveniles and adults).

While the sprat, Sprattus sprattus (L.), may live for up to a total of six years, at the end of which time the total length can exceed 150 mm, the fishery in British waters is based primarily on the second, third and fourth year classes (Robertson, 1936, 1938; De Silva, 1973). Historically, the sprat was a major contributor to the fishery of the Bristol Channel and Severn Estuary (Matthews, 1933; Lloyd, 1942). Although this fishery has declined during recent decades, the sprat has remained an important component of the teleost fauna of the region. This point is illustrated by the observation that S. sprattus was by far the most abundant of all teleosts in plankton samples taken throughout the Bristol Channel between the spring and autumn of 1974 (Russell, 1980). While length–frequency data were provided by Russell (1980) for these recently spawned sprat and there is comparable information for those sprat which form the basis of the commercial fishery in the Bristol Channel (Lloyd, 1942), no such data are available for those members of the population which are known sometimes to enter the Severn Estuary in considerable numbers (Lloyd, 1941).

INTRODUCTION

Several authors (Cable & Hunninen, 1942; Dogiel, Petrushevski & Polyanski, 1958) noted that fishes while being kept in aquaria, lose the intestinal parasites with which they had become infested in nature. Up to now no quantitative examinations have been made on this subject. A better knowledge of the behaviour of parasites of fish in captivity seems to be of interest for several reasons.

The possible elimination of intestinal parasites by quarantining the host fish would be of importance in case of parasites which are able to complete their life-cycle in the aquarium and which might provoke mass-infection.

We report for the first time the effects of vehicle traffic and beachgoer trampling on macrobenthic communities of Amazonian sandy beaches. Sampling was performed during four consecutive months with different beach use intensity in 2017 (before, during vacation, and two months after the vacation period) on three contrasting beaches with regard to disturbance (Urban: Atalaia; Intermediate: Farol-Velho; and Protected: Corvinas) in the intertidal zone along two equidistant transects at seven equidistant sampling stations from the high-tide water mark to the swash zone. At each sampling station, four biological and sediment samples were randomly collected. Also, in each station, the sediment compaction was determined using a manual penetrometer. Physical sediment variables remained constant over time in all beaches, whereas differences were found in sediment compaction over the months. Macrobenthic community differences in density and richness among months were observed at Atalaia and Farol-Velho beaches. In contrast, Corvinas beach remained constant throughout the study period. Furthermore, the vulnerability of the polychaetes Thoracophellia papillata, Scolelepis squamata and Paraonis sp. indicates that they might be potential indicators of recreational activity impact.

Macrofaunal community structure was examined in a shallow sublittoral sea grass bed (Zostera marina L.) and adjacent unvegetated sediment in the River Yealm, Devon, south-west Britain, on a single sampling occasion in August 1995. The presence of Zostera had a significant influence on macrobenthic community structure in the River Yealm. Samples from inside the sea grass bed were characterized by significantly higher numbers of individuals and species, as well as by greater species richness and high faunal dominance (i.e. low evenness) compared with the unvegetated samples. High faunal dominance within the sea grass bed was attributable to the large numbers of a few species (e.g. the polychaetes juvenile capitellids, Spio filicornis, Exogone hebes, Nereis pelagica and the tanaidacean Apseudes talpa), while increased species richness was a result of a large number of additional rare (1–2 individuals) species. The greatest number of individuals was found in samples with the highest sea grass biomass. Multivariate ordination revealed a distinct separation of macrofauna communities from vegetated and unvegetated sites. Significance testing with ANOSIM shows that there were significant differences in community structure between vegetated and unvegetated habitats.

Using video and image analysis techniques we analysed the response of swarms of the mysid Paramesopodopsis rufa to food and predatory attack. After food was added to the tank, mysid aggregations initially (up to 45 s) increased in volume. Subsequently volume decreased significantly until it was smaller than the initial level. After a period of ~12 h during which no food was added, the swarm expanded to near its original volume. These changes are interpreted as resulting from a need by individuals to optimize food capture and protection. The pattern of volume changes in response to food was independent of aquarium size but the magnitude of the changes was reduced in a smaller tank.

Predatory attacks on mysid swarms were simulated using a model fish which ‘swam’ a single pass along the tank driven by an electric motor. Models (latex-covered real preserved fish), represented two different attack styles: ambush (seahorse Hippocampus abdominalis); and lunging (Australian salmon Arripis trutta). ‘Swimming’ speeds resembled those measured for real fish i.e. 0·5–2·0 cm s-1 for seahorse and 15 cm s-1 for salmon. Again changes in swarm volume were recorded. No obvious response by the swarm to the approaching seahorse was apparent; the aggregation simply parted to allow the fish through. No tailflips were seen among the mysids. The swarm resumed the original volume rapidly after the fish had passed. Approach of the salmon was evidently detected from further away, escape reactions were frequent and energetic, and tailflipping was common. After the fish had passed, it took longer for the original swarm volume to be restored. These results suggest that seahorse ambush techniques have evolved to minimize warning of the predator's approach. When the salmon ‘menaced’ the swarm at seahorse speeds, it appeared the mysids still reacted as though it was a ‘normal’ salmon attack so the fright response was not just a function of speed of attack.

Dynamic changes in swarm volume seem to be a useful simple index of motivational state of individuals.