FACTORS AFFECTING PREY CHOICE AND FEEDING TECHNIQUE IN THE CARNIVOROUS SNAIL EUGLANDINA ROSEA FERUSSAC

Euglandina feeds on other gastropods either by quickly suckingthe contents from the shell, or by swallowing the prey whole,which can be more time consuming. When Euglandina were offeredprey species of various sizes, they preferentially consumedthe smaller individuals, and often swallowed these whole. Handlingtime increased with decreasing density since swallowing preywhole became more frequent at the lower densities. The relationship between prey size, predator size, handlingtime and feeding technique was examined. For the two feedingtechniques observed, handling time increased exponentially withthe size of the prey and decreased exponentially with the sizeof the predator. Predators of intermediate size tended to swallowprey whole more frequently than did the smallest and largest. These data are interpreted in terms of the animal behaving insuch a way as to balance its rate of intake of both organicmatter, which resides mainly in the soft parts, and of calcium,which resides mainly in the shell. (Received 11 July 1988; accepted 31 October 1988)     

THE COURTSHIP OF EUGLANDINA ROSEA FERUSSAC

Courtship of Euglandina rosea commences with trail followingculminating in the pursuing snail mounting the shell of thepursued from the rear. A vigorous head waving display then occursand is terminated after about 15 min by a short quiescent periodduring which the lower animal turns its head to face its ownshell. Copulation takes place whilst one snail is still mountedon the shell of the other, but in a head to head position broughtabout by the twisting of the neck of the lower animal. It lastsup to four hours. (Received 24 April 1984;     

INHIBITION OF CONTRACTION RESPONSES OF HYDRA

The contraction reponse ot hydra to intermittent light stimulationmay be inhibited by exposing the animal to reduced glutathione(GSH). Such inhibitory acthity is dependent on: (1) the concentrationof GSH; (2) the pH of the medium; (3) previous exposure to GSH;and (4) the nutritional state of the animal. Hydra adapt tolO^–5 M GSH so that after approximately an hour the frequenciesof lightinduced contractions are restored to control levels.Such adaptation to GSH is due to changes occurring within theanimal rather than to the degradation of the glutathione molecule.S-methyl glutathione blocks contractions in response to light,showing that the sulfhydryl group is not essential for inhibition.Analogs with sterically large groups substituted for the sulfhydrylgroup, such as oxidized glutathione and S-acetyl glutathione,have no inhibitory activity. These compounds, however, reducethe inhibitory effect of GSH, indicating competition for theGSH receptor. Contractions of hydra in response to intermittent mechanicalagitation are also inhibited by GSH. The duration of inhibitionis dependent on the GSH concentration. Both oxidized glutathioneand S-acetyl glutathione reduce the inhibitory effect of GSH. Hydra adapted to the dark for 24 hours show a marked suppressionof contractions in response to mechanical agitation when exposedto light. On exposure to light, such animals elongate to approximatelyone and a half times their dark adapted length, and are relativelyinsensitive to agitation. The mechanisms by which such stimuliinhibit the contraction responses of hydra remain to be determined.     

Some prospects for investigating hydra cellsIn vitro

Summary and Conclusions Over the past 15 years great strides have been taken in the laboratory culture of intact hydra, and in the discovery and elucidation of a wide variety of fundamental biological problems that can be studied using this organism. In the present article I restricted myself mostly to research being conducted in my laboratory on: environmental ions; uptake of food particles: a possible role of CO₂ gas; the unusual collagenous nature of nematocyst capsules; the reproduction of cells from a hydra mutant in otherwise “normal” hydra; and activation of behavioral contraction responses by reduced glutathione and tyrosine. In addition, Dr. Campbell (4) and Dr. Haynes (5) have reviewed much research in developmental biology that is currently taking place using hydra, and which similarly could be enhanced through culture of hydra cells. Although in this review I have placed some emphasis on the present difficulties of raising the cells of hydrain vitro, I still believe that hydra cells can and should be cultured. The culture of cells from an animal at the tissue level of organization is a challenge that ought not to go unanswered.     

Measuring Glutathione-induced Feeding Response in Hydra

Hydra is among the most primitive organisms possessing a nervous system and chemosensation for detecting reduced glutathione (GSH) for capturing the prey. The movement of prey organisms causes mechanosensory discharge of the stinging cells called nematocysts from hydra, which are inserted into the prey. The feeding response in hydra, which includes curling of the tentacles to bring the prey towards the mouth, opening of the mouth and consequent engulfing of the prey, is triggered by GSH present in the fluid released from the injured prey. To be able to identify the molecular mechanism of the feeding response in hydra which is unknown to date, it is necessary to establish an assay to measure the feeding response. Here, we describe a simple method for the quantitation of the feeding response in which the distance between the apical end of the tentacle and mouth of hydra is measured and the ratio of such distance before and after the addition of GSH is determined. The ratio, called the relative tentacle spread, was found to give a measure of the feeding response. This assay was validated using a starvation model in which starved hydra show an enhanced feeding response in comparison with daily fed hydra.     

Neuroendocrine Control Mechanisms in Shell Formation

The brain of Helisoma duryi contains several neurodendocrinecentres. Factors) present in the cerebral ganglia are thoughtto be involved in normal shell growth while neurosecretory substancespresent in the visceral ganglion are involved in the repairof damaged shell. In Lymnaea stagnalis a growth hormone is producedby the cerebral ganglion which stimulates periostracum formationand the calcification of the inner shell layer. The second effectis thought to occur through the action of a mantle edge calciumbinding protein. In Helisoma, mantle collar is able to produce the periostracumin vitro. The presence of brain from a fast growing donor increasesthe amount of periostracum produced by a mantle collar froma slow growing animal. This effect is further enhanced by theremoval of the lateral lobes. The periostracum produced by fastgrowing animals has a higher glycine content than that producedby slow growing snails. The presence of dorsal epithelial tissueenhances the incorporation of calcium into periostracum formedin vitro. These findings suggest that a single factor is present in thebrain of fast growing Helisoma which modulates shell formationrates in vivo and periostracum formation in vitro.     

SEXUAL DIMORPHISM OF NUCELLA LAPILLUS (GASTROPODA: MURICIDAE) IN NORTH WALES, UK

Multivariate statistical methods were employed to examine sexualdimorphism in size and shape of Nucella lapillus collected from 16sheltered sites along coasts of Anglesey and the Lleyn Peninsula, NorthWales, UK. Females were significantly larger than males in overallsize; among 12 relative measures of shell shape, two ratios (shellwidth/shell length and aperture length/shell length) were significantlydifferent between males and females, but these differences usuallydecreased with increasing age (shell length). The observed hypoallometricdimorphism could be a result of selection on increased femalefecundity, which may be positively correlated with shell sizein N. lapillus as in other gastropod species. (Received 22 November 1999; accepted 10 April 2000)     

Non-budding Hydra: Form Regulation and Bud Induction

Form regulation and bud induction were studied in a non-buddingstrain of Chlorohydra viridissima. Regeneration at a cut surfacein a column piece with an existing hydranth was observed andfound to be dependent on the column length Another aspect ofform regulation, formation and control of supernumerary tentacles,was investigated by grafting. Supernumerary tentacle formationin long polyps can be suppressed by implants of hypostomal orsubhypostomal tissue. Non-budding hydra can be induced to bud by implanting smallpieces of normal tissue into their columns. The cellular basisof this process was investigated by means of grafting, radioautography,and histological methods. No differences in the proportionsor appearances of the cell types were observed between non-buddingand normal animals. However, induced buds have higher proportionsof interstitial cells and their derivatives (nerves and nematoblasts)than do normal buds. Many of these interstitial cells and derivativesoriginate from cells in the grafted implant. Normal tissue fromwhich interstitial cells have been previously removed will notinduce buds in non-budding hydra. The non-budding syndrome is probably related to a deficiencyin interstitial cell differentiation. If nerve cells are involvedin bud initiation and form regulation, these results suggestinterstitial cells of non-budding hydra are unable to transforminto sufficiently active and/or numerous nerve cells to controlthose processes.     

SPATIAL PATTERNS OF SHELL SHAPE OF THREE SPECIES OF CO-EXISTING LITTORINID SNAILS IN NEW SOUTH WALES, AUSTRALIA

The shape and relative weight of the shell have been shown tovary intraspecifically and interspecifically in a number ofspecies of gastropods, including many different littorinids.These differences give rise to different shell forms in differenthabitats. In those species which have non-planktotrophic development,differences in shell form among shores have been usually explainedin terms of natural selection because exposure to waves supposedlyfavours light shells with large apertures, while predation bycrabs on sheltered shores favours elongated, thick shells withsmaller apertures. Differences in shell shape among speciesfound at different heights on the shore have been explainedin terms of resistance to desiccation and temperature. Suchvariables would tend to act on a relatively broad-scale, i.e.causing differences among heights on a shore or among shores.Rates of growth, which might vary at much smaller scales withina shore, have also been shown to affect the shapes of many shells. In this study, the shape and relative weight of shells of threespecies of co-existing littorinids (Littorina unifasciata, Bembiciumnanum and Nodilittorina pyramidalis) were measured. These speciesall haveplanktotrophic development and they are found on manyshores where there is no evidence that they are preyed uponby crabs. Before explanations of shell shape are proposed, itis necessary that patterns of variation, within different partsof ashore and among different shores are clearly documented.These patterns were measured at a number of different spatialscales within and among replicate shores with different amountsof wave exposure. Large and small specimens were included toallow intraspecific comparisons among snails of different sizesfound at different heights on the shore. The results showedsignificant differences among shores in shape and relative weightof shells, but these differences could not be explained by exposureto waves. In addition, snails of different sizes and differentspecies did not show the same patterns although they were collectedfrom the same sites. Importantly, the shell shape of Liuorinaunifasciata varied significantly among sites at approximatelythe same height within a shore. These differences could notbe clearly correlated with density, mean size nor exposure towaves. The only consistent pattern was a decrease in relativeaperture size in specimens living higher on the shore. Modelsthat have commonly been proposed to explain shape and relativeweight of shells in other species of gastropods are not adequateto explain the small- and large-scale variation of the measurementsdescribed here. It is proposed that any selective advantageof shell morphology and the effects of any variables on thedevelopment of shell morphology in these species can only beidentified after appropriately designed and replicated fieldexperiments. (Received 4 March 1994; accepted 13 September 1994)     

THE EARLY LIFE-CYCLE STAGES OF HYDROBIA VENTROSA AND HYDROBIA NEGLECTA WITH OBSERVATIONS ON POTAMOPYRGUS JENKINSI

The egg mass of Hydrobia neglecta contains a single egg, whilethat of H. ventrosa contains up to three eggs. At hatching H.neglecta has a significantly greater shell length than H. ventrosaand the late embryos and young snails of the two species canbe separated according to the pigmentation of the head region.The young snails can also be separated on the basis of surfaceornamentation of the shell and comparisons with the closelyrelated H. ulvae and Potamopyrgus jenkinsi show how the basicpattern of shell sculpturing differs in the four species. Thesedifferences are discussed in relation to the mode of development. (Received 14 February 1980;     

Functional Morphology of Perihelia conradi Relative to Shell-Penetration

The pholad, Penitella conradi, is found along the Californiacoast in the calcareous shell of the abalone, Haliotis rufescens.These pholads penetrate the abalone shell, and when they breakthrough the inside of the shell they cease boring, secrete acallum, and then become sexually mature. The normal adult isa stenomorphic form,defined by Bartsch as an animal whose sexualmaturity is induced by over-crowding or insufficient substratumin which to bore. In the case of P. conradi, sexual maturityis always induced by the spatial limits of the substratum, thatis, the relatively thin abalone shell. The role of mechanical abrasion by the valves of P. conradiis minor. Experiments indicate that the teeth of P. conradiare worn at a greater rate than the polished shell of the abalone. The boring process in P. conradi proceeds mainly by chemicaldissolution of the calcareous substrate. The pathway of thesolvents is unknown. It may be through the organic matrix, orthe solvent may react directly with the crystals. Mechanicalabrasion helps to remove loosened crystals and/or organic matrixwhich are then carried to the exterior by the ciliary currentsflowing in through the pedal gape and out through the exhalentsiphon.     

A FIELD TECHNIQUE FOR RECORDING THE ACTIVITY OF LIMPETS

A field technique for recording both temporal and spatial parametersof activity in limpets was tested on a Tyrrhenian populationof Patella rustica Linnaeus which shows definite homing behaviour.Timing of foraging excursions was recorded using reed switchesactivated by a magnet glued to the shell apex. The ‘lsquo;athome-away’ status of each animal was continuously screenedthroughout one month by interfacing the sensors with a computer.Moreover, individual excursions were minutely reconstructedby using a moto-graphic technique which combined LED-tracking(nocturnal activity) and instantaneous photography (daytimemovements). An original wave-meter was designed to monitor thesea-status during the study period. The quality of the temporaland spatial data obtained with this technique is evaluated,and further improvements of the technique are discussed. (Received 24 October 1989; accepted 25 January 1990)     

The hydra GSH receptor. Pharmacological and radioligand binding studies

1. The GSH-induced feeding response of hydra has been studied using pharmacological and biochemical methods. 2. Dopaminergic agonists inhibit the response, whereas dopaminergic blocking agents increase it. Phosphodiesterase inhibitors completely inhibit the feeding response. 3. The specific binding of the competitive inhibitor of feeding response, [3H]glutamate, to hydra cellular fractions has been evaluated, and a strong GSH-sensitive binding has been observed in a nematocyst-rich fraction. 4. After pharmacological reduction of the nematocyst number, both feeding response and glutamate binding are severely reduced. 5. Ca2+ ions must be present for the feeding response to occur, whereas glutamate binding occurs both without Ca2+ and in the presence of EDTA.     

REMOTE BIOMINERALIZATION IN DIVARICATE RIBS OF STRIGILLA AND SOLECURTUS (TELLINOIDEA: BIVALVIA)

Deposits composed of aragonite prisms, which were formed afterthe outer shell layer, have been found at the posterior steepslopes of divaricate ribs in two species of Strigilla and anothertwo of Solecurtus. These prisms have their axes oriented perpendicularto the outer shell surface and differ in morphology from fibresof the surface-parallel composite prisms forming the outer shell.They display crystalline features indicating that, unlike crystalsforming the outer shell surface, their growth front was free,unconstrained by the mantle or periostracum. These particulardeposits are called free-growing prisms (FGPs). In these generathe periostracum is clearly not the substrate for biomineralizationand, upon formation, does not adhere to the steep slope of ribs,but detaches at the rib peak and reattaches towards the posterior,just beyond the foot of the posterior scarps of ribs. In thisway, a sinus or open space developed between the internal surfaceof the periostracum and the outer shell surface along each steeprib slope. These spaces could remain filled with extrapallialfluid after the mantle advances beyond that point during shellsecretion. FGPs grow within this microenvironment, out of contactwith the mantle. Other species with divaricate ribs do not developFGPs simply because the periostracum adheres tightly to both ribslopes (which are never so steep as in Solecurtus and Strigilla).FGPs constitute one of the rare cases of remote biomineralizationin which aragonite is produced and direct contact with the mantlenever takes place. (Received 22 November 1999; accepted 20 February 2000)     

IN VITRO RECALCIFICATION OF ORGANIC MATRIX OF SCALLOP SHELL AND SERPULID TUBES

Organic matrix was isolated from the shell of the bivalve Argopectenirradians by decalcification. The capacity of the matrix toinitiate formation of crystals similar in form and orientationto the crystals of normal shell was investigated. Decalcifiedshell matrix placed in an inorganic recalcification solutioninitiated the formation of elongate crystals in parallel arrangementcorresponding to the parallel orientation observed in the matrixfibers and similar to the orientation of the long crystals innormal shell. The detailed form of the crystals deposited invitro was different from that of the normal shell crystals.Electron diffraction analysis of remineralized matrix demonstratedthat the material was calcite, the mineral of normal shell. In contrast, the calcareous tube of the serpulid Hydroides dianthushas crystals lacking uniform arrangement and a matrix whichdoes not have a well-oriented structure. The decalcified tubematrix was recalcified and the mineral posited showed some evidenceof normal orientation. The results demonstrate that matrices of Argopecten shell andHydroides tube can induce crystal formation in vitro. Sincethe soluble matrix would be expected to be removed during decalcification,the observed in vitro effects apparently involve the insolublematrix. (Received 19 June 1984;     

Colchicine, nocodazole and trifluralin: different effects of microtubule polymerization inhibitors on the uptake and migration of endosymbiotic algae in Hydra viridis

Hydra viridis (= Chlorohydra viridissima) the freshwater coelenterate, is symbiotic. Each individual animal harbours Chlorella sp. in its endodermal cells. The symbiosis may be disestablished, the partners grown independently, and then re-established experimentally. The most effective method to produce alga-free hydra was developed by Pardy (1976). In this study algae from homogenized H. viridis, English (= European) strain, were either used directly or first grown in pure culture and then injected to re-establish the symbiosis. The uptake of algae grown in culture was compared with that of algae released directly from fresh hydra. Fewer cultured algae were taken up. Four strains were tested: English, Carolina, Frome, and Jubilee. Each takes up a characteristic number of Chlorella when injected in excess. Colchicine, nocodazole and trifluralin, were tested for their effects on either uptake or migration. Colchicine had no effect. Nocodazole and trifluralin reduced both the number of algae taken up and the rate at which they were transported to the distal region of the hydra digestive cell. The effects of these drugs tended to be proportional to the concentration between 10(-8) and 10(-5) M.     

Enzymatic indices of respiration and ammonia excretion: relationships to body size and food levels

Enzyme indices of zooplankton respiration, citrate synthase(CS), and ammonia excretion rate, glutamate dehydrogenase (GDH),were measured in cultures of Artemia franciscana (San FranciscoBay) feeding in a 25-fold range of concentration of the algaDunaliella salina. Enzyme activities per animal were regressedagainst body size (expressed as dry weight or protein) in theform of the allometric equation, log Y = log a + b logW. CSactivity was related to size with a scaling exponent (b) of1.133 in terms of dry weight and 0.864 in terms of protein.GDH scaling exponents were 1.283 and 0.978 for dry weight andprotein, respectively. In cases where these variables are measured,it is essential that the size structure of populations and communitiessampled is taken into account, otherwise false conclusions maybe drawn. Despite specific growth rate variation from 0.117to 1.188 day^–1, no differences in CS or GDH activity couldbe attributed to feeding level or growth rate effects. Suchenzymatic indices, which represent only maximum potential metabolicrates, may therefore be poor predictors of actual rates in vivo.     

Tumour-promoting phorbol esters rapidly inhibit bud formation in hydra

Summary The effects of tumour promoters and carcinogens on bud formation were investigated in an attempt to clarify the primary process of bud formation in hydra. Treatment with 1.0ng/ml 12-O-tetradecanoylphorbol-13-acetate (TPA), phorbol-12,13-didecanoate (PDD) or mezerein added immediately after feeding rapidly and completely inhibited the formation of new buds in Hydra japonica. Treatment with TPA 3–6 h after feeding also suppressed bud formation 24 h later, but suppressed buds appeared 48 h later. Buds suppressed by TPA also formed in the presence of a diluted homogenate of hydra and during starvation. Carcinogens, such as benzo(a)pyrene and 20-methylcholanthrene, did not have an inhibitory effect on bud formation within 2 days. The tumour promoters and carcinogens used in this experiment did not inhibit the regeneration of tentacles. These results indicate that tumour-promoting phorbol esters, but not carcinogens, rapidly suppress the process by which the formation of buds is initiated by hydra, and the effects of these esters depend on the timing of treatment after feeding.     

Excavation of Boreholes by the Gastropod, Urosalpinx: An Analysis by Light and Scanning Electron Microscopy

Penetration of shell by the muricid gastropod, Urosalpinx cinereafollyensis, is accomplished by successive alternating periodsof (a) chemical activity by the accessory boring organ (ABO), and (b) rasping by the radula. This paper reports on the functionsof the radula and of the ABO in producing the characteristicgeometry of the borehole, andon the effects of radular teethand of the ABO secretion on the microscopic anatomy of the surfaceof the borehole during the process of shell-boring. Radulae of U. c. follyensis and the surfaces of incomplete boreholesin the shell of Crassoslrea virginica, Mytilus edulis, and Myawere examined by means of light and scanning electron microscopy.Hardness tests of radular teeth andshell of prey demonstratedthat marginal teeth are harder than rachidian teeth, and thatthe range of hardness of rachidianteeth overlaps that of thethree species of shell. Rasping is carried out by two, occasionallythree, of the five rachidiancusps. Rasping patterns are shallowand asymmetric. Rachidian teeth are worn to the base with use;marginal teeth wear onlyslightly as they are employed mainlyin feeding. The distance between the tips of rachidian cuspscorresponds with the interval between the parallel cusp tracesrasped by them in shell. During each rasping period, snailsscrape off about 1/10 to 1/5 of the surface of the chemicallytreated area of the bottom of the borehole. Dissolution of shell is accomplished by secretion from the secretorydisk of the ABO. With each application of the ABO,most or allof the radular marks of the previous rasping period are erasedby solution of a thin layer of shell. The pattern of etchingis specific for each of the species of shell studied. In oysterand mussel shell, initial solubilization occurs through theorganic, non-mineralized, prism sheaths, exposing prismaticforms shown by other workers to be distinctive for these species,and then proceeds into the organic-calcareous structure of individualprisms. Etching of Mya shell revealed no fundamental prismaticform. Shell-penetration includes dissolution of both organiccomplexes and CaCO₃ crystals. Shell-boring by this snail is principally a chemical process,and the geometry of the borehole is generally a reflection ofthe morphology of the ABO.     

Predation of cockles (Cerastoderma edule) by the whelk (Buccinum undatum) under laboratory conditions

The feeding rate and behaviour of whelks (Buccinum undatum)offered cockles (Cerastoderma edule) in laboratory experimentswere examined. When presented with cockles in a range of sizes(10–40 mm), 14 B. undatum (34.6–88.3 mm),held individually in aquaria, consumed a wide size range ofcockles. Small whelks (<40 mm) consumed cockles (<23 mm),whereas large whelks, (>60 mm) ate a greater numberof larger cockles (>30 mm) and a wider size range ofcockles (12–40 mm) than smaller whelks. The majority(90%) of the shells of the predated cockles were undamaged andthe few (<10%) that were damaged showed only slight abrasionsto the anterior and posterior shell margin. Filmed observationsof B. undatum feeding on C. edule showed a method of attackthat has not previously been reported and involved the use ofthe whelk's foot to asphyxiate the cockle or to pull the shellvalves apart. No filmed evidence was found for the previouslyreported shell ‘wedging’ technique for prising openthe closed shell valves of C. edule, although 10% of the shellsof consumed cockles in feeding experiments had damaged shellmargins. (Received 4 April 2007; accepted 30 June 2007)