For the largely immature population of crabs studied no difference in length weight relationships could be detected between males and females unless fresh weight was used for comparison. Females and immature males showed isometric growth throughout their life while mature males showed allometric growth. The use of length, fresh weight, dry weight and ash-free dry weight for the basis of comparative metabolic studies is discussed. Oxygen consumption rate was found to be related to the 0.799 power of body dry weight or ash-free dry weight for both males and females and resting and active rates. Scope for activity was constant at 3.7 across the entire body weight range. A marked diurnal rhythm of oxygen consumption rate was found, the exact form of which depended on season being bi-modal in short day length and uni-modal in long day length. The beat rates of heart and scaphognathite were found to show a high degree of correlation throughout all phases of the daily cycle. A typical short period rhythm of beat rates is shown during the resting phase. Ventilation volume showed a linear relationship with scaphognathite beat rate up to active rates of pumping. Above this ventilation efficiency was impaired. The short period rhythm had a period of almost exactly twenty minutes, and was divided into three phases, the high-rate, the low-rate and the changing phase. In order to conserve metabolic stores, the duration of the low-rate phase is increased, at the expense of the level and duration of the high-rate phase, with increasing starvation. Percentage utilisation of oxygen was at its highest during the high-rate phase (40 - 42%) and it appears that efficient oxygen exchange is limited to the rates of pumping of the active phase. Possible functions for the short period rhythm are discussed in the light of this observation. Haemocyanin was more or less absent from the local population of Cancer but not Carcinus and Portunus. Reasons for this are discussed. A new method for measurement of haemocyanin oxygen capacity was used. Effectiveness of oxygen uptake by the blood was low due to the lack of haemocyanin, but effectiveness of oxygen removal from the ventilatory water was high due to a decrease in ventilation:perfusion ratio. Ventilation:perfusion ratio did not change greatly with increased starvation. The physiological significance of these measurements is discussed.

Clibanarius virescens (Krauss) is a common and abundant hermit crab along the East coast of South Africa. Despite this, its biology is poorly known, both in South Africa and throughout the rest of its range in the West Indo-Pacific region. This study focuses on the descriptive analysis of the shell resource used by C. virescens and of the effects of this resource on crab populations. The underlying hypothesis of the study is that biogeographically imposed gradients in the morphology of intertidal gastropod shells used by hermit crabs affect hermit crab population parameters. The gradient of potential change in the shell resource was captured by sampling at 12 localities, encompassing the range of C. virescens in South Africa. Seasonal changes in shell use, population structure and reproduction at a single locality (Cape Recife) were recorded over a period of 13 months. The breeding season of C. virescens at the southern extreme of its range extended from December to June. The population structure shows some seasonal change, but no clear trends emerge. The shell resource changed substantially in nature over the region studied. Based on shell use, localities clustered into separate southern and northern groups with a break occurring between Dwesa and Coffee Bay. Southern localities were characterised by use of Burnupena cincta, B. lagenaria and B. pubescens. Northern localities were characterised by the use of Morula granulata, M. nodosa and Peristernia forskalii. Intertidal shells used by C. virescens show fewer adaptations to predation in southern localities than shells from northern localities. Southern shells ii are relatively large, light and have wider apertures than those from northern localities which are generally smaller, heavier and have decreased aperture widths. Shell parameters affect population size-distributions as southern crabs were larger and heavier than northern crabs. C. virescens show sexual size dimorphism in which male crabs uniformly dominate the larger size classes at all localities. Differences in the sex ratio between males and females show more variable patterns. Most southern localities show no difference in the number of male and female crabs, but most northern localities show a skewed sex ratio in favour of females. Shell use and population size distributions of females affect reproductive output. Southern females produced significantly larger clutches than northern females. Reproductive output was related to crab mass and shell volume. Shell use patterns conform to the biogeographical regions in the range of the study and have a clear effect on both the population size distributions and reproductive output of Clibanarius virescens.

Thesis (M.A.)--Boston University / The pericardial organs are neurosecretory structures situated within the pericardial cavity of stomatopod and decapod crustaceans. Their location in the pericardium is such that blood approaching the heart must flow directly over them. This arrangement facilitates the distribution of pericardial organ secretions to all parts of the organism. It is not known how many different neurohormones are secreted by the pericardial organs, but at least one of these has been shown to act as a strong cardioexcitor. Electron microscopy of pericardial organs has revealed the presence of membrane-bounded granules, approximately 1500 A in diameter, which are believed to contain the neurosecretory material. An attempt was made here to isolate the cardiaexcitor by means of differential centrifugation of crude 0.9 M sucrose homogenates of pericardial organs from two species of Cancer. Live Homarus heart served as bioassay material. Cardioexci tatory effects were found in material which sedimented below 17,000 x g. On two occasions another active sediment was found at 71,000 x g. The present data is in agreement with the hypothesis that the cardioexcitor is contained within neurosecretory granules. However, a definitive statement to this effect cannot be made, as sediments were not checked microscopically. Presumptive evidence is offered for the existence of a second type of neurosecretory granule.

Hydrostatic pressure sensing is used by aquatic animals to estimate depth and to synchronize behaviour with the tides. Pressure sensors examined to date depend on the compression of a fluid, making them susceptible to temperature change. Despite this, the effects of temperature on pressure sensing have not so far been researched. This thesis examined the effects of temperature on the afferent firing rate of thread hair pressure receptors in the crab Carcinus maenas. It tested the hypothesis that for sensors responding positively to rising pressure, an increase in temperature should counteract any contraction in volume, thereby leading to a weaker neural response; vice versa, a stronger response was predicted for a temperature decrease. A novel system was developed which allowed the simultaneous application of sinusoidal pressure change from 150 to 350 mbar and cycles of temperature, typically spanning between 16 and 22 °C, while extracellular recordings were made en passant from afferent nerves innervating statocyst thread hairs. Motor programmes were designed to stimulate thread hairs sensitive to clockwise and anticlockwise rotation through continuous or interrupted bouts of oscillation within the horizontal plane. During constant pressure, raising temperature led to increases in spike frequency and amplitude, with Q10s between 3 and 5 for spike frequency but less than 2 for amplitude. Cooling caused the elimination or decrease of pressure responses while increasing them on heating, thereby contradicting the aforementioned hypothesis of temperature mimicking pressure change. Changes in the timing of pressure responses were also observed. In preparations which were non-responsive to pressure change, temperature change led to bursts in firing at the peaks or troughs of pressure cycles in 28 of 42 preparations, with evidence for recruitment of formerly silent units. The results could not be fully explained under the existing model for pressure sensing by thread hairs, highlighting the necessity for further anatomical studies.

No description available.

No description available.

No description available.

Graduation date: 1950

Thesis (Ph.D.)--Murdoch University, 2006. / Thesis submitted to the Division of Science and Engineering. Includes bibliographical references (leaves 159-171).

Thesis (M.S.)--Georgia Southern University, 2008. / "A thesis submitted to the Graduate Faculty of Georgia Southern University in partial fulfillment of the requirements for the degree Master of Science." Directed by Sophie B. George. ETD. INDEX WORDS: Fiddler crabs, Population density, Salt marsh, Survey techniques Includes bibliographical references (p. 28-30) and appendices.