Hermit Crab Eupagurus Bernhardus Research Articles

Enterospora sp., an intranuclear microsporidian infection of hermit crab Eupagurus bernhardus

Recent work at our laboratory has led to the discovery of a new genus of microsporidian parasite residing in the family Enterocytozoonidae. The type species of this new genus, Enterospora canceri, is an intranuclear parasite infecting the hepatopancreatocytes of the decapod crustacean Cancer pagurus. Here we provide the second description of a parasite within the genus Enterospora, this time infecting the hermit crab Eupagurus bernhardus from U.K. waters. The pathological manifestation and ultrastructural features of the hermit crab parasite are very similar to those described for E. canceri. Further taxonomic comparisons based upon ultrastructural and molecular affinities of Enterospora are now required to define firmer links between this new genus within the Enterocytozoonidae and all other microsporidian families. The opportunistic nature of the discovery of a second intranuclear microsporidian within the Crustacea suggests that their presence may be more common than in higher animal groups.

The occurrence of the eunicid polychaetesIphitime cuenotiFauvel andI. PaguriFage & legendre in crabs from the Scottish West Coast

Abstract During an investigation into the occurrence of various crab species in the Oban (West of Scotland) area, Iphitime cuenoti was found infesting the branchial cavity of Liocarcinus puber, L. corrugatus, L. depurator, Carcinus mamas, Cancer pagurus, Hyas araneus and Macropodia longirostris caught within, or on the sandy mud below, the Laminaria forest. The same crab species obtained from sandy habitats, and crabs peculiar to such a habitat (Portumnus latipes, Liocarcinus holsatus and Corystes cassivelaunus) did not harbour the polychaetes. Three or more worms were commonly found in each Liocarcinus host, the highest number recorded, in L. puber, comprising 9 adult and at least 98 juveniles, the latter being found between the gill lamellae. Over 90% of both L. puber and L. corrugatus were infested, 35% of L. depuratot, but less than 10% of any of the other species. The largest worms (up to 80 mm alcohol-preserved length) were found in L. puber and L. corrugatus. Worms were found to have either simple or slightly bifurcate branchiae, or multifurcate branchiae. Worms with simple branchiae rarely reached 40 mm in length, usually possessed jaws which exceeded 700 μm in length, and were never found to contain eggs. These are regarded as putative males, and histological evidence from three specimens confirms this suggestion. Only Iphitime with multifurcate branchiae were found to contain eggs, and were also the largest worms, but their jaw length was very variable, ranging from 0-1030 μm with little or no relationship to the length of the worm. The smallest worms, 3 mm in length, were found between the gill lamellae throughout the year, but mainly from December to August. In multiple infestations there appeared to be one dominant female which probably inhibited maturation of companion worms, and it is postulated that once this female vacates, there is a sequential maturation and spawning of subordinate worms. The greatest number of mature worms, and the largest worms, occurred during October and November, but because of the extended larval settlement period it is a matter of debate whether the worm is an annual, or has a more extended lifetime. Iphitime paguri was found occupying the apical whorl of4.6% of Buccinum undatum shells and 2.6% of Neptunea antiqua shells occupied by the hermit crab Eupagurus bernhardus. The worm is very fragile and, being rare, there is insufficient data to define its biology. The longest worm was 50 mm (alcohol- preserved length) and the largest jaw length 760 μm; there appeared to be an inverse relationship between length of worm and jaw size, and no worm over 25 mm had jaws larger than 250 μm. All ovigerous worms had small jaws. Nereis fucata was found in 2.6% of Neptunea antiqua and 7.1% of Buccinum undatum shells occupied by the hermit crab. It was not found associated with Iphitime paguri.

Chemical composition and caloric content of egg and zoea of the hermit crabeupagurus bernhardus

1. Chemical composition and caloric content of egg and zoea of the hermit crabEupagurus bernhardus have been determined and the cumulative efficiencies of yolk utilization calculated. 2. The cumulative efficiencies of yolk utilization for different constituents were 70.0%, 55.3%, 79.4% or 35.0% for dry weight, caloric content, protein or fat. 3. Since the efficiencies with which the different constituents of yolk utilized vary, the chemical composition of the developing eggs undergoes considerable changes. While fat and caloric content showed remarkable decreases, water, ash and protein contents of the eggs increased. 4. Of 0.0722 cal expended on metabolic processes of the embryo, only 28.4% was drawn from the oxidation of protein, while fat contributed as much as 66.6%. 5. Considerable quantities of inorganic salts (0.77µg/egg) are absorbed from the sea-water by the developing egg.

Das Belichtungspotential der isolierten Retina des Einsiedlerkrebses (Eupagurus bernhardus L.) in Abh�ngigkeit von den extrazellul�ren Ionenkonzentrationen

1.The action potential of the isolated retina of the hermit crab Eupagurus bernhardus L. resulting from exposure to light has been measured with external electrodes under constant stimulus conditions. Three measurements of the retinal action potentials (RAP's) were taken to observe the changes of the RAP's quantitatively: a) The amplitude h max of the maximum; b) the amplitude h e of the plateau, measured at the end of the stimulus, for taking the shape quotient h max /h e ; c) the peak-amplitude-time t max. 2.The RAP's of the retina in a standard physiological saline are compared with those of the retina in salines of different ionic composition while osmotic pressure and p h were kept constant. 3.Increasing K+-concentration reduces the amplitude h max of the RAP's gradually, which is zero at 500 mM K+/l. The peak-time t max decreases with increasing K+-concentration up to 50 mM K+/l, whereas at higher concentrations it increases. In contrast to this fact h max/h e increases up to 50 mM K+/l and decreases above this concentration (Fig. 3). 4.Increasing Ca++-concentration reduces h max (zero above 350 mM Ca++/l) and t max. h max/h e rises up to a Ca++-concentration of about 30 mM Ca++/l; whereas at a higher Ca++-concentration it decreases again (Fig. 6). When the Ca++-concentration is very low the fall of the RAP is much slowed down and the plateau h e extremly rises. In a Ca++-free saline which contained 1 mM/l Ethylendiamintetraacetic acid (EDTA) the retina lost its irritability reversibly (Fig. 8). 5.The amplitude of the RAP's is augmented with increasing Mg++-concentration up to 10–30 mM Mg++/l and decreases above this concentration (Fig. 11). When the saline contains virtually no other cations but Mg++ (367 mM/l) the amplitude of the RAP is small (20%) but not zero. 6.In a buffered isotonic NaCl-solution as well as in a saline in which all the Cl--ions are substituted by SO4 ---ions the amplitude of the RAP's is higher but the shape of the RAP's is changed in the same way as in other solutions with very low concentrations of Ca++. 7.All the changes of the RAP's described so far are reversible. 8.Even when the retina is kept in a salt solution containing sodium in a very low concentration (ca. 3–5 mM/l, the sodium substituted by choline+-ions) for 5 hours the amplitude h max of the RAP does not change significantly but the shape: the peaktime t max is longer, h max/ h e is much greater. Afterwards when the retina is brought into standard saline again, the amplitude h max increases, t max remains almost unchanged and h max/h e , decreases strongly (Fig. 17). 9.Substitution of all the Na+-, Ca++- and Mg++-ions by choline+-ions results in a decrease of the amplitude h max, a lengthening of t max and a small increase of h max/h e . 10.Substitution of all the NaCl by glucose decreases the amplitude h max, lengthens t max very much and decreases the value of h max/h e but little. Afterwards, when the retina is brought into standard saline again the effect of the glucose solution on the amplitude h max is only little reversible: h max increases very little, t max decreases strongly and h max/h e increases (Fig. 21). 11.With increasing external K+-concentration the resting potential decreases. The changes of the resting potential cause the changes in the shape of the RAP's. 12.The presence of a small concentration of Ca++-ions outside of the cell membrane is obviously necessary for the ability of the cell membrane of the photoreceptor to increase its ionic permeability consequent to stimulation by light. Above a Ca++-concentration of about 1 mM/l the raise of permeability of the cell membrane during illumination is smaller with increasing Ca++-concentration. The velocity of the changes in permeability is augmented, especially of those changes concerned with the fall of the RAP. The effect of Mg++-ions is somewhat similar to that of Ca++-ions, but much weaker. 13.The changes of the RAP are mainly determined by the low Ca++-content when the retina stays in the NaCl- or sulfate saline. 14.Choline+-ions probably greatly increase the raise of permeability of the cell membrane for the divalent cations Ca++ and Mg++ during excitation. 15.It is suggested that under normal conditions in Eupagurus the amplitude of the RAP is determined primarily by the Na+-concentration gradient over the receptor cell membrane. But also the divalent cations Ca++ and Mg++ contribute to the amplitude of the RAP, especially after the retina has been treated with choline chloride.

Ver�nderungen des Belichtungspotentials der Retina des Einsiedlerkrebses (Eupagurus bernhardus L.) bei Vergiftung des Stoffwechsels und bei Adaptation

1. The action potential of the retina of the hermit crab Eupagurus bernhardus L. resulting from exposure to light has been measured with external electrodes. 2. Three measurements of the retinal action potentials (RAP's) were taken to observe the changes of the RAP's quantitatively: a) the amplitude of the maximum hmax, to characterize the height of the RAP's; b) the amplitude of the plateau he,measured at the end of the stimulus for taking the shape quotient hmax/he; c) the peak amplitude time tmax. 3. The changes of the RAP's under the influence of metabolic inhibitors (2,4-Dinitrophenol 0,2 mM/1; Potassiumcyanide 1,0 mM/1; Sodiumazide 1,0 mM/1) have been studied under constant stimulus conditions. 4. Under the influence of the metabolic inhibitors the RAP's soon become smaller and finally under these conditions the excitability of the retina is lost. 5. Some minutes after washing out the inhibitor RAP's again can be evoked, these increasing in size with time. 6. The three inhibitors manifest similar effects on the RAP's; however, they differ in reaction time. 7. The excitability of the retina, which has been lost by poisoning, was not restorable by use of positive and negative polarizing currents. 8. The changes of the RAP's in the course of dark adaptation under constant stimulus conditions and the changes by different intensities of the stimulating light are measured and compared with the alterations of the RAP's induced by metabolic inhibitors. 9. When the intensity of the light stimuli increases, the amplitude hmax of the RAP's and the shape quotient hmax/hegrow in size and the peak amplitude time tmax decreases. 10. In the first phase of the influence of the metabolic inhibitors the changes of the height of the RAP's are similar to those produced by decreasing intensities of the stimuli, whereas the changes of the shape measured by the shape quotient hmax/heand tmax are similar to those produced by increasing intensities of the light stimuli. In the second phase of the inhibitors' action, both, the changes of height and shape of the RAP's are similar to those produced by decreasing intensity of the stimuli. 11. The changes of the RAP's under the influence of the inhibitors are very similar to the changes of the RAP's in the course of dark adaptation, when compared in the reverse direction of time. They are also rather similar to the changes of the RAP's when the resting potential of the photoreceptor cells is decreased under the influence of increasing potassium concentration in the extracellular solution. 12. It is suggested that under the influence of metabolic inhibitors the resting potential of the photoreceptor cells will decrease and the concentration of rhodopsin probably also will decrease.

Das Belichtungspotential der Retina des Einsiedlerkrebses in Abh�ngigkeit von der Temperatur

1. The action potential of the isolated retina of the hermit crab Eupagurus bernhardus L. resulting from exposure to light has been measured at temperatures between 5° and 25° C. 2. With increasing temperature the time course of the retina action potential (RAP) shortens. Latency tla and peak-amplitude-time tmax of the RAP decrease. The slopes of rising and falling phase of the RAP steepen, the former less than the latter. 3. The temperature-coefficients (Q10's) of all the time-values of the RAP's measured have been larger than 2. 4. At increasing temperature initially the amplitudes of the RAP's rise, while further increase of temperature above 10–15° C the RAP's decrease. 5. All observed temperature-dependent changes of the RAP were fully reversible. 6. The amplitudes of the two components K I and K II of the RAP show a similar temperature-dependence. 7. The range of validity of the Bunsen-Roscoe-law depends on temperature: at short lasting stimuli the amplitude of the RAP depends on the product of stimulus intensity x stimulus duration (I · τ). Under the experimental conditions here described this has been found at temperatures of 25° C up to stimulus durations of 10–20 msec, at 5° C up to stimulus durations of 60–120 msec. 8. The observed RAP's and their changes with temperature have been interpreted in the following way: The RAP occurs as the result of a chemical reaction of the visual pigment induced by exposure to light. This inturn produces a fall of the electrical resistance of the membrane of the photoreceptor cell. The restoration of the dark-adapted state requires metabolic processes. The decrease of the membrane resistance of the photoreceptor cell during illumination is relatively small at low and high temperatures as compared to medium temperatures. The decrease of the resistance during exposure to light and consequently the amplitude of the RAP decrease above 10–15° C with increasing temperature since at higher temperatures the falling phase of the RAP is more accelerated than the rising phase. Among the processes responsible for the rising phase of the RAP there is one photochemical temperature-independent reaction. On the other hand the processes responsible for the falling phase of the RAP all are temperature-dependent. Below 10–15° C the decrease of the electrical resistance during light-exposure rises with increasing temperature. Since in the experiments described the retina has not been fully dark-adapted the amplitude of the RAP largely depends on the speed of dark-adaptation, which shows a strong positive temperature-dependence. The speed of dark-adaptation determines the dependence of the amplitude of the RAP on temperatures below 10–15° C. Furthermore at low temperatures the system which is responsible for the permeability changes of the cell membrane presumably becomes directly inactivated at low temperatures — thereby exhibiting a behaviour similar to that of a nerve fiber showing the phenomenon of cold blockade. The temperature-dependence of the resistances in the retina as well as the temperature-dependence of the range of validity of the Bunsen-Roscoe-law have been taken into account when evaluating the measured curves of the RAP's.

Biliverdin in the Eggs of Nereis fucata

Nereis fucata (Savigny) is a polychaete worm living in the gastropod shells carried by the hermit-crab Eupagurus bernhardus (L.) at Plymouth. The heteronereis or breeding stage found with hermit-crabs during late February was found to contain apparently ripe, blue eggs in the cœlom. The eggs were removed by slitting the body-wall of fresh worms, rinsed in sea water to remove haemoglobin, and separated from cœlomic cells by repeated centrifuging. The pigments in the eggs were extracted into a methanol–sulphuric acid mixture (19 : 1), when a turquoise-blue solution was produced. A purple pigment remained in the eggs; the nature of this pigment is being investigated. The original blue colour of the eggs was apparently due to the mixture of the purple pigment and the turquoise extract. The turquoise solution was filtered through glass wool, diluted with an equal volume of water and shaken with chloroform. The chloroform layer became bluish-green. This was evaporated to dryness in vacuo, and the pigment redissolved in methanol. The absorption spectrum of this solution showed a sharp peak at 392 mµ and a broader peak at 650 mµ, with minimum absorption at 500 mµ. The addition of zinc acetate and iodine produced a brilliant pink fluorescence in ultra-violet light. When more iodine was added the fluorescence became green. The presence of biliverdin was confirmed by the production of a purple colour, with a spectral absorption maximum near 490 mµ, by the addition of concentrated nitric acid, and by the destruction of the blue-green pigment with concentrated sulphuric acid.