AN ULTRASTRUCTURAL STUDY OF SPERMATOZOA OF HELIX ASPERSA AND HELIX POMATIA (GASTROPODA, PULMONATA)

Spermatozoa of the pulmonates Helix aspersa Müller andH. pomatia Linnaeus are examined in detail using transmissionelectron microscopy (TEM). Important features such as the acrosome,perinuclear sheath, nucleus and terminal region of the midpieceare described for the first time. Also presented are the firstultrastructural observations on spermatozoa from spermatophoresin any pulmonate gastropod (H. aspersa). No morphological differencescould be found between sperm taken from spermatophores and thosewithin the hermaphrodite duct in H. aspersa. Spermatozoa ofH. aspersa and H. pomatia snow all the characteristics of euthyneuranspermatozoa, namely: a helically-keeled nucleus; distinctivearrangement of acrosomal components (apical vesicle, acrosomalpedestal), and extremely elongate midpiece (axoneme and glycogenhelix enclosed by matrix and paracrystalline layers). The spermnucleus of both species is short, and the midpiece also formsthe terminal portion of the spermatozoon (glycogen piece absent).The extraordinary positioning of the acrosome in H. aspersa—reflectedbackwards from the nuclear apex—is not observed in H.pomatia, though a perinuclear sheath (possibly another acrosomalcomponent) is present in sperm of both species. Helix spermatozoaare compared with other euthyneuran sperm and briefly discussedfrom the systematic viewpoint. Present address: Department of Zoology, St. Lucia, 4067, Brisbane,OLD, Australia (Received 23 May 1988; accepted 17 August 1988)     

GEOGRAPHICAL PATTERNS OF GENETIC DIFFERENTIATION IN THE LANDSNAIL HELIX ASPERSA MuLLER (GASTROPODA: PULMONATA)

In order to investigate the initial processes responsible forthe geographical distribution of the Mediterranean landsnailHelix aspersa, populations from 64 locations in Maghreb andin Europe were studied at 17 enzyme loci by both starch andpolyacrylamide gel electrophoresis. Allele frequencies and genotypedistributions were analysed to provide information on populationstructure and genetic differentiation among populations. Valuesof Nei's unbiased (D) and Rogers (R) genetic distances led tothe formation of two main groups, namely Europe-west Algeriaand east Maghreb (average D = 0.182). Such splitting supportedthe pattern of anatomical variation recently described. Twosamples from Morocco were excluded from these groups becauseof an average D = 0.224. Within this Moroccan entity, geneticdivergences did not distinguish the ‘giant’ snailsH. a.maxima from the brownsnails H. a. aspersa. Such biochemicalsimilarities among morphological heterogeneity throws the subspecificstatus of H. a. maxima into question. Values of fixation indicesindicated that the greatest differentiation between samplesoccurred on the Maghreb territory ( = 0.393). The patterns of population differentiation are discussed inrelation to past geological and historical events. Thus, threescenarios, not mutually exclusive, are considered: the disjunctionof populations by plate tectonics during the Tertiary, the formationof geographically isolated populations during the Pleistoceneglacial/interglacial cycle and the possibility of human introductionas early as the Neolithic period. (Received 9 December 1992; accepted 11 November 1993)     

EFFECTS OF WOUND HEALING ON ZINC DISTRIBUTION AND ALKALINE PHOSPHATASE ACTIVITY OF HELIX ASPERSA (GASTROPODA: PULMONATA)

Helix aspersa were loaded with ⁶⁵zinc and after 2 and 5 daysstarvation there was no significant reduction in the zinc concentrationof the digestive gland and shell. Wounding of the optic tentacle,foot tissue and partial shell removal of H. aspersa resultedin deposition of ⁶⁵zinc in the wound area. Alkaline phosphataseshowed no increase in concentration at the sites of wounding. (Received 15 October 1985;     

THE INFLUENCE OF INGESTIVE CONDITIONING ON FOOD CHOICES IN THE LAND SNAIL HELIX ASPERSAMULLER (GASTROPODA: PULMONATA: STYLOMMATOPHORA)

An experiment of food choice in one-day-old naïve landsnail Helix aspersa Müller was carried out, involving threephases. First, a training period on a monophagous diet of leafdiscs of Taraxacum officinale or Urtica dioica was given for1, 5, 10, 15 or 30 days. The area of leaf discs consumed byeach snail during this stage was assessed. In the intermediatephase, the animals were not fed for 24hours. Finally, food choicewas tested over 24 hours, when animals could eat leaf discsof each species of plant usedfor training. A coefficient offood preference for Urtica dioica was calculated (UPC = areaof Vrtica leaf disc consumed/area of Urtica and Taraxacum discsof leaves consumed for 24 hours). The length of the training phase did not reduce the percentageof individuals preferring the plant previously consumed. Onthe contrary, after 15 days of monophagous diet, animals formerlyfed on Urtica showed a coefficient of food preference for Urticasignificantly higher than Taraxacum fed animals, and after 30days of training this phenomenon was more pronounced. Thus,during the choice test, snails ate more of the previously eatenplant leaf. Our experiment highlighted the feeding behaviourplasticity of H. aspersa. The significant correlation betweenthe area of Urtica eaten during the training phase and the coefficientof food preference for Urtica is discussed. (Received 10 April 1994; accepted 10 January 1995)     

FIELD OBSERVATIONS ON FEEDING OF THE LAND SNAIL HELIX ASPERSA MULLER

Feeding of the land snail Helix aspersa (Müller) was observedat monthly intervals. Three natural populations in Galicia (NW-Spain)were studied. At two sites only a few plants constituted thebulk of the diet and in spring the snails' diet had the highestdiversity (H'). In the third population feeding and distributionof Helix aspersa (Müller) were observed in a small plotwith permanent patches of Urtica dioica. Nearly one half offeeding snails fed upon Urtica dioica. Most of the other observations wereon Mentha suaveolens, Ranunculus repens and Gramineae. The diversity ofthe snails' diet showed seasonal variation with the maximumin the autumn months. Comparison between the availability ofthe different plant species and their contribution to the snails'diet showed that the snails did not eat at random; Urtica dioicawas eaten much more than expected from its occurrence and grasseswere strongly under-represented in the snails' diet. Temporalchanges of availability were significantly correlated with the amountseaten in the case of Urtica, but not for the other food plants.The distribution of the snails in the plot was significantlycorrelated with that of Urtica. Chemical analyses of the foodplants revealed Urtica as the species with the higher protein,ash and calcium contents. The strong preference of Helix aspersafor Urtica dioica could be explained by the value of Urticaas food or by its suitability as habitat for the snails. The largestproportions of green material in the snails' diet occurred inthe spring and juveniles ate more green material than adultsin the three populations. (Received 16 March 1998; accepted 30 November 1998)     

EVOLUTION, DURING DIGESTION, OF THE BACTERIAL FLORA IN THE ALIMENTARY SYSTEM OF HELIX ASPERSA (GASTROPODA: PULMONATA): A SCANNING ELECTRON MICROSCOPE STUDY

The use of scanning electron microscopy (SEM) allowed a studyof the distribution of bacteria in the various digestive organsof the snail Helix aspersa Müller. The bacteria are enclosedby mucous secretions (mucous film or mucous grains) and sometimesattached on the cilia of some of the digestive walls. Accordingto the food that was given to the snails, different morphologicaltypes appeared, two of which dominated. Adult snails were fasted for 4 days, given a dehydrated artificialfood and then sacrificed at different times during digestion.The presence of bacteria may be related to the time of digestion.In fact, bacteria seem to accompany the food mass; they developmostly in the stomach and in the intestine where they may helpdigest the food. Fasting or hibernating snails do not possess bacteria in thealimentary lumen or on the digestive walls. However, the residualfaeces localized in the distal, intestinal lumen, lodge greatquantities of bacteria. From these results, the endogenous or/and exogenous existenceof the bacterial flora in alimentary system of Helix aspersais discussed. (Received 26 June 1989; accepted 16 October 1989)     

THE INFLUENCE OF HUMIDITY, PHOTOPERIOD, AND TEMPERATURE ON THE DORMANCY AND ACTIVITY OF HELIX LUCORUM L. (GASTROPODA, PULMONATA)

The dormancy of Helix lucorum from N. Greece is controlled primarilyby low humidity. Photoperiod and temperature have no directeffect, except in the anomalous combination of long cool daysor short hot days. Adults hibernate more readily than juveniles.The duration of hibernation (before rejection of the calcareousepiphragm) is only slightly shorter at high temperatures. (Received 15 December 1985;     

WATER CONTENT OF SLUGS (GASTROPODA:PULMONATA) IN NATURAL HABITATS, AND THE INFLUENCE OF CULTURE CONDITIONS ON WATER CONTENT STABILITY IN ARION ATER (LINNE)

10 species of slug were collected from a variety of habitats.Within species, water contents were relatively constant, andit was concluded that they were maintained by water uptake,mainly through the integument, together with appropriate cryptozoicbehaviour. Weights of A. ater individuals held outdoors didnot show large daily fluctuations. ^*Present address: Department of Zoology, East Mailing ResearchStation, Maidstone, Kent ME19 6BJ (Received 15 June 1982;     

THE EFFECT OF OPTIC TENTACLE REMOVAL ON THE TRANSMITTER CONTENT OF THE GIANT SEROTONIN CELL OF HELIX ASPERSA

Abstract— There is a giant serotonin-containing neuron in each metacerebral ganglion of the snail Helix pumntia. Much of the amine is localized in small granular vesicles (COTTRELL and OBSORNE, 1970) and evidence for serotonin having a transmitter role in each giant neuron is very strong (COTTRBLL, 1970a, b). It is shown that the content of serotonin in each giant neuron is reduced by ablation of the optic tentacle. Maximum depletion of amine (about 70 per cent) was observed at 6–8 days after the operation. Unilateral depletion followed removal of only one tentacle. To examine the observations more closely, electrophysiological experiments were also made to determine any neuronal connection between the tentacles and the serotonin-containing neurons. No evidence was found for the presence of an axon from either giant neuron in the nerves leading to the tentacles. Stimulation of the nerves supplying the tentacles caused both depolarization and spike firing, and hyperpolarization and inhibition of the giant neurons. It is possible that the depletion of serotonin following ablation of the optic tentacles results from an interruption of the nerve fibres mediating in one or both of the observed types of input.     

NOTES ON THE INTRODUCED TERRESTRIAL PULMONATA (GASTROPODA:MOLLUSCA) OF NEW ZEALAND

The New Zealand Pulmonate fauna contains 22 naturalized terrestrialspecies. For each, a bibliography is given for the New Zealandliterature and comment made on its biology and distribution.Vertigo ovata SAY and Oxychilus draparnaldi (BECK) are newlyrecorded from New Zealand. (Received 11 February 1981;     

THE STRUCTURE OF THE SECONDARY GILLS OF SIPHONARIA CAPENSIS (GASTROPODA: PULMONATA)

The secondary gill of the pulmonate limpet Siphonaria capensisis located in the dorsal portion of the mantle cavity. Eachlamella of the gill is triangular in shape and bears ciliarytufts which have a density of about 400/mm². The free ends ofsome of the cilia are enlarged biconcave discs. Each gill lamellais covered by a single layer of cuboidal (4x4 µm) epitheliumon each side, separated by a central haemocoelic space. Ciliatedand mucus secreting cells are interspersed amongst the epithelialcells. The haemocoelic space is spanned at intervals by trabeculaecontaining longitudinal and transverse muscle fibres. (Received 29 August 1986;     

ON THE RESPIRATORY QUOTIENT OF LUPINUS ALBUS AS A FUNCTION OF TEMPERATURE

The temperature characteristics for the oxygen consumption and CO₂-production of the germinating seeds of Lupinus albus were previously found to be different. It was predicted qualitatively that the respiratory quotient of the seed should be a function of temperature. A quantitative treatment is presented here, relating the change of the respiratory quotient with temperature and the temperature characteristics. Experimental results agree satisfactorily with the calculated value.     

CALCIUM PHOSPHATE GRANULES IN THE REPRODUCTIVE SYSTEM OF OXYCHILUS ATLANTICUS (GASTROPODA: PULMONATA)

The presence of connective interstitial cells in the wall ofseveral organs of the distal reproductive system in Oxychilus atlanticusis described by means of scanning electron microscopy (SEM).Connective interstitial cells extend from the distal part of thevas deferens to the penis, being the dominant cell type of large portionsof the epiphallus as well as in the whole penial caecum (=flagellum).These cells are highly mineralized and are characterized bythe presence of large amounts of solid spherules (up to 4 mmin diameter) in their cytoplasm. A semi-quantitative evaluationby X-ray microanalysis demonstrates that calcium and phosphorusare the main elements of the spherules. Their function is unknown,but they could aid in copulation or they could assist the survivalof the transferred spermatozoa. (Received 7 June 1999; accepted 8 September 1999)     

THE ONCHIDIACEA (GASTROPODA, PULMONATA) OF HONG KONG WITH A WORLDWIDE REVIEW OF THE GENERA

The Onchidiacea are a superfamily of mainly marine intertidal,slug-like pulmonates. Twelve genera are recognizable, and theseare redefined. Four of these genera are represented in HongKong, each by a single species, and these are recorded herein.Two of these are new; a third has not been seen since it wasoriginally figured in 1850. ^*Present address: Palmers Sixth-Form College, Grays, Essex. (Received 18 August 1983;