The limpet gut consists of a long coiled tube lined by a ciliated columnar epithelium, into which open the ducts of the salivary and digestive glands. Six sections can be distinguished: the buccalcavity, oesophagus, stomach, style sac, intestine and rectum. The oesophagus can be subdivided into a dorsal food channel and a series of lateral pouches forming the oesophageal gland. The intestine is divisible into sections designated A, B, C, D and E. Ultrastructural and histochemical analyses revealed nine cell types, seven of them glandular. A single type of gland cell lining the tubules of the salivary gland produces a viscous secretion that lubricates the radula and entraps particles rasped from the substratum. Mucous cells occur in the buccal cavity, dorsal food channel and rectum; in the rectum, mucus aids defaecation, but elsewhere it entraps loose particles that are consequently transported to the stomach. The only extracellular enzyme, an amylase derived from the gland cells of the oesophageal gland, is mixed with the food in the dorsal food channel. Ciliated and unciliated columnar cells lining the ducts of the digestive gland, stomach, style sac and anterior intestine, release blebs of cytoplasm into the lumen to consolidate loose particles into a faecal rod that is rotated along the intestine. Clavate gland cells and possibly basal gland cells in the posterior intestine, cover the faecal rod with their secretion to form a durable rod. The vacuolated digestive cells of the digestive gland, digest food intracellularly releasing undigestible residues in spherules of cytoplasm, these are bound into a liver string by the proteinaceoussecretion of the basophilic cells. Both these cell types and the amylase-secreting cells exhibit phases of activity, but only that of the latter is related to the tidal cycle. Tritiated D-glucose was absorbed by the oesophagus, intestine and digestive gland by a mechanism inhibited by 2,4-DNP and phloridzin. The mechanisms operating in the oesophagus and posterior intestine were sodium-dependent. Fluid movements from the intestinal lumen to the blood occurred.

The Manila clam, Ruditapes philippinarum, was introduced into the British Isles in the 1980s for the purpose of aquaculture in order to take advantage of the rapid growth rate and high profitability of this non-native species. The decision to import the Manila clam, was based on the findings of a report commissioned by the Ministry of Agriculture Fisheries and Food which determined that the Manila clam would be able to be grown to marketable size faster than the local species Ruditapes decussatus, but would not be able to reproduce due to the inclement seawater temperature regime around the British Isles. Within four years of its introduction into Poole Harbour in Dorset, the Manila clam had successfully reproduced and by 2004 it had naturalised in the Harbour. This thesis sets out to determine the factors that influence reproductive and recruitment success of the Poole Harbour population of Manila clams and to determine what factors could influence the further dispersal of the Manila clam along the South and South Eastern coastline of England. The population of Manila clams at Holton Mere in Poole Harbour was quantitatively sampled on a monthly basis, with some omissions, from June 2009 until August 2012. For each sample month, the density and population dynamics of the population were estimated. From February 2010 until August 2012 the condition index of the population was estimated on a monthly basis. The population dynamics of the Holton Mere population were influenced by fishing pressure with the removal of the majority of clams over the minimum landing size of 35mm. Condition index followed a seasonal pattern with high condition in summer and low condition in winter. Recruitment success in the Holton Mere population was inconsistent, with successful recruitment events coinciding with higher levels of condition index. A study to correlate environmental parameters with clam condition index, using long term monitoring with a multi-parameter sonde were undertaken in Poole Harbour between July 2011 and July 2012. Seawater temperature and food availability was found to positively correlate with condition index. Experiments determined that predation by the European shore crab, Carcinus maenas has the potential to influence the success of recruitment events due to high levels of predation on newly settled and juvenile clams. Reduced salinities and low temperatures influence the rate of predation of juvenile Manila clams by crabs. Salinity influences behaviour in both adult and larval Manila clams, with burial by the adults and swimming in the larvae ceasing at salinities below 18psu. Manila clam larvae actively swim through haloclines into areas of reduced salinity. Manila clam larvae are able to tolerate salinities as low as 10psu for 24 hours with low levels of mortality. The Manila clams’ tolerance to reduced salinity allows it to colonise areas of marginal habitat where competition is low. Predicted increasing seawater temperatures will allow the Manila clam to extend its range northwards by causing cold water species to vacate ecological niches for the Manila clam to occupy and to improve the consistency of reproductive success. The Manila clam is now established along the Southern coastline of England and is unlikely to disappear. As such it should be classed as a naturalised species and managed in the same way as native species. The Manila clam is likely to spread northwards in the future and will provide both economic and ecological benefits in the form of new fisheries and also prey for local species including wading birds. The high growth rate and versatility of the Manila clam would allow it to be used in polyculture systems and be grown in habitats that were previously deemed unsuitable for bivalve culture.

Gastropods, like many other marine invertebrates undergo a two-stage life cycle. As the adult body plan results in narrow environmental tolerances and restricted mobility, the optimum opportunity for dispersal occurs during the initial larval phase. Dispersal is considered to be a major influence on the evolutionary trends of different larval strategies. Three larval strategies are recognised in this research: planktotrophy, lecithotrophy and direct development. Planktotrophic larvae are able to feed and swim in the plankton resulting in the greatest dispersal potential. Lecithotrophic larvae have a reduced planktic period and are considered to have more restricted dispersal. The planktic period is absent in direct developing larvae and therefore dispersal potential in these taxa is extremely limited. Each of these larval strategies can be confidently inferred from the shells of fossil gastropods and the evolutionary trends associated with modes of development can be examined using both phylogenetic and non-phylogenetic techniques. This research uses Cenozoic gastropods from southeastern Australia to examine evolutionary trends associated with larval mode. To ensure the species used in analyses are distinct and correctly assigned, a taxonomic review of the six families included in this study was undertaken. The families included in this study were the Volutidae, Nassariidae, Raphitomidae, Borsoniidae, Mangeliidae and Turridae. Phylogenetic analyses were used to examine the relationships between taxa and to determine the order and timing of changes in larval mode throughout the Cenozoic. Traditionally, planktotrophy has been considered the ancestral mode of development. However, using maximum parsimony and maximum-likelihood analysis, this research suggests that the ancestral developmental mode cannot be confidently determined in gastropods from southeastern Australia. Similarly, evidence that transitions between larval strategies might be reversible contradicts the general view that regaining the specialised structures associated with planktotrophy is so difficult that it is considered extremely unlikely to occur. When the timing of switches in larval mode was examined they were found to be scattered at different points in time rather than clustered to specific periods and therefore no inference can be made as to the likely factors driving transitions between larval modes. The correlation between mode of development and macroevolutionary trends was examined using non-phylogenetic techniques. The results do not concur with the hypothesis that species with planktotrophic larvae will exhibit wider geographic ranges, longer species durations and lower speciation rates then lecithotrophic or direct developing taxa. The analyses are thought to be hindered by a strong preservation bias and gaps within the fossil record. The quality of the fossil record and the congruence between phylogenies and stratigraphy is examined using the Stratigraphic Consistency Index, the Relative Completeness Index and the Gap Excess Ratio.

Cephalopod populations typically display life-history traits such as semelparity, fast growth, and rapid response to environmental variation. The short lifespan of most squid species means that populations typically consist of single non-overlapping generations; the success of future generations therefore depends upon the ability of present generations to produce viable offspring. Pronounced inter-annual fluctuations in cephalopod population sizes reflect, at least in part, variability during the embryonic, hatchling and juvenile phases. As post-hatch survival is critically dependent upon the successful capture and consumption of zooplanktonic prey, variability in hatchling morphology (e.g. size, shape, presence of abnormality) and physiology (e.g. thermal tolerance) are likely to exert significant influence upon survival. This thesis investigates embryonic variability in two temperate loliginid squid: the Northern Hemisphere Loligo forbesi Steenstrup 1856 and the Southern Hemisphere Sepioteuthis australis Quoy and Gimard 1832. Developmental variability in L. forbesi and S. australis largely manifests via chromatophore pattern. The plasticity and thermal sensitivity of chromatophore characters exceed those of standard morphological characters (e.g. body shape and size). Elevation of incubation temperature is associated with reduced chromatophore number and heightened pattern asymmetry. Correlation between temperature and hatchling phenotype is sufficiently strong to permit estimation of mean thermal history from measure of multiple chromatophore and morphological characters. Increased water temperature is associated with increased frequency of morphological abnormality. In situ assessment of embryonic development in S. australis indicates ~89% egg viability within egg strands. Significant intra-seasonal differences in incidence of mortality and abnormality appear to reflect changes in environmental conditions. Embryos reared under fluctuating (field) thermal conditions grow faster than those reared under stable (aquaria) thermal conditions. Despite variation in size-at-hatch, no concomitant differences are observed in mantle muscle structure. The results of this thesis indicate no significant relationship between hatchling phenotype and underlying physiological processes (i.e. plasticity). I discuss the idea that quantification of embryonic development in cephalopods has relevance to both fisheries management and biomonitoring.

Many parasitic digeneans are of medical and veterinary importance and therefore developing methods to accurately identify them and understand their evolutionary epidemiology is crucial to disease diagnosis, surveillance and control. An integrative approach using molecular and morphological data was applied in investigating digenean species transmitted by lymnaeid snails in the UK. Radix auricularia, R. balthica, Lymnaea stagnalis and Stagnicola fuscus were identified by DNA sequencing of the ITS2 and cox1 genes. They were recorded to transmit a total of 13 digenean species belonging to six families. The parasites were identified by sequencing appropriate nuclear and mitochondrial genetic markers and were morphologically described. The study presents the first molecular identification of Diplostomum pseudospathaceum and Tylodelphys clavata (Diplostomatidae), Cotylurus brevis (Strigeidae), Plagiorchis maculosus (Plagiorchiidae), Trichobilharzia szidati (Schistosomatidae), Echinostoma revolutum, Echinoparyphium aconiatum, and Hypoderaeum conoideum (Echinostomatidae) from the UK. Australapatemon sp. (Strigeidae) and Echinoparyphium sp. could only be identified to genus level and require further investigation. Trichobilharzia franki was molecularly identified for the first time from Scotland. Echinoparyphium recurvatum and Lecithodendrium linstowi (Lecithodendriidae) were molecularly identified for the second time in the UK. Trichobilharzia species are causative agents of human cercarial dermatitis which is currently regarded as a re-emerging disease in Europe and E. revolutum, Ep. recurvatum and H. conoideum are zoonotic agents of echinostomiasis. Diplostomum pseudospathaceum and T. clavata cause diplostomiasis in aquaculture. The cercaria of the bat trematode L. linstowi is described for the first time and its molluscan host identified as R. balthica.

It has long been recognised that the life cycles of the major exploited ommastrephid squid species are closely related to oceanographic features, and that environmental variability may provide a significant stimulus for variability in the species abundance and distribution. In this thesis, the relationship between oceanographic processes and population variability for the ommastrephid squid <i>Martialia hyadesi</i> in the western South Atlantic is investigated using a geographic information system (GIS) (ARC/INFO^(c) v. 7.2.1., ESRI Inc. 1999). From this analysis, it was clear that the oceanographic environment of the region does influence the abundance and distribution of <i>M. hyadesi</i>. However, the precise mechanisms by which this occurs are not determined. In the west of the study region, near the Patagonian Shelf, it appears that the distribution of <i>M. hyadesi</i> is intimately linked to that of the Falkland (Malvinas) Current, and that variability in the behaviour of this current may influence the annual abundance of the squid in the Patagonian Shelf squid fisheries. In the waters around the Falkland Islands (Malvinas), it appears that the 'population' of <i>M. hyadesi</i> may exist in two alternate states depending on its abundance. In most years, the squid occur at low densities, widely dispersed both in time and space. In exceptional years, the squid are far more abundant and are both spatially and temporarily aggregated. Although, no small juvenile or paralarval specimens of <i>M. hyadesi</i> were collected during this study, such specimens were collected for other squid species, and their distribution was successfully related to environmental factors. Both water mass type and water depth influenced the number of squid caught, and appeared to influence the species composition of the catches. Evidence was also found supporting the hypothesis that <i>M. hyadesi</i> does not occur near South Georgia during the austral summer and is extremely unlikely to spawn there.

No description available.

The Robertsonian polymorphism (numerical change in the chromosome complement by centric fusion or fission) in the dog-whelk (Nucella lapillus, Mollusca: Gastropoda) has been known and studied sporadically for almost 50 years. However, the possible causes, consequences and proposed correlations of this phenomenon remain enigmatic. Nucella lapillus (2n = 26 to 36), has undergone a marked reduction in chromosome number from its ancestral form; most other muricid species have a diploid chromosome number in the range 2n = 60- 70. Correlations have been proposed between chromosome number (or karyotype) and habitat (wave exposure), and also directly or indirectly with allozymes, shell shape and physiology. However, firm conclusions are lacking due to either, insufficient knowledge of the karyotypes in the populations studied, or the fact that any correlations are not consistent throughout the broad geographic range. This study reviews all the past research on the chromosomal polymorphism in N. lapillus, advances the karyology of this species by successfully labelling individual chromosomes through silver-staining of nucleolar organizer regions (NORs) and fluorescence in situ hybridisation (FISH) with rDNA and telomeric probes, and proposes a new system of nomenclature for this polymorphism. Knowledge of the geographic variation in chromosome number and karyotype is advanced by studying around 70 populations throughout the range of N. lapillus (mainly in the UK, but also the USA and northern and southern Europe). Evidence is shown that, (1) the polymorphism is far more widespread geographically than was previously thought; (2) more than five pairs of metacentric chromosomes are involved in the Robertsonian polymorphism; and (3) inversions also occur in some populations. Putative links between chromosomal polymorphism in N. lapillus and Darwinian fitness are reviewed in the light of the new findings and more recent work on other species; data are presented on fecundity, fertility, inter- and intra-individual variation in karyotype, selection within populations (adults v. embryos, homo- v. heterozygotes) and a possible genetic/karyotypic link with phenotype (Dumpton syndrome, a reproductive abnormality). Cytogenetic records for other muricids are also reviewed and karyotypes and chromosome lengths of four other species (Ocenebra erinacea, Thais haemastoma, Murex trunculus, Ocinebrina aciculata) are recorded for the first time. Genome size (DNA content) of 8 species of muricid, including the 2n=26 and 2n=36 forms of N. lapillus, are determined by Feulgen densitometry and compared in the context of evolutionary studies on the family. Although chromosome number and haploid length in N. lapillus has been reduced, its genome size is actually greater than all but one of the other muricids studied, and consequently has a much higher DNA packing ratio (&gt;13000). Whether the chromosomal variation in N. lapillus represents polymorphism, polytypy, or speciation in progress remains unresolved, but substantial advances have been made in this dissertation and the required direction and focus for future work are clarified.

Ovorubin, apoprotein and ovorubin reconstituted from apoprotein and carotenoid were prepared from the eggs of Pomacea canaliculata australis, by adsorption on alumina CB or on carboxymethyl cellulose. Electrophoresis indicated an homogeneous preparation, but solubility tests indicated two components, very similar except for spectral differences. Paper chromatography revealed the presence of all the commonly occurring amino acids. 20% of the ovorubin molecule consisted of carbohydrate (glucosamine, galactose, mannose and fucose). The carotenoid component is in the trans form. Ovorubin was shown to possess a strong antitryptic activity, comparable with that of ovomucoid, which was not lost on removal of the carotenoid. The apoprotein was not more readily denatured than ovorubin, except after several precipitations with acetone. No direct correlation between changes in spectrum and inhibitory activity was demonstrated, neither was the spectrum modified by reaction with trypsin, Acetylation of amino groups of the apoprotein did not prevent inhibition, but did prevent recombination with the carotenoid. Ovorubin did not inhibit acetylated trypsin. A protein with antitryptic activity was isolated from eggs of Pila ovata gordoni, but was not extensively investigated. Trypsin slowly attacked ovorubin; pepsin produced a quite rapid fall in inhibition of trypsin and, after addition of trypsin and Chymotrypsin, the degradation product was isolated and shown to retain some antitryptic activity although the protein moiety was smaller. Ovorubin was shown to inhibit chymotrypsin and a protease from Aspergillus oryzae. Indications were obtained that an enzyme produced by B. subtilis was also inhibited. The nature of the second component in ovorubin preparations was discussed. The properties of ovorubin were compared with the proteins of hens' eggs; in composition and antitryptic action ovorubin is very similar to ovomucoid. A possible bacteriostatic role was suggested for ovorubin.

No description available.