FORAGING BEHAVIOUR OF TERRESTRIAL GASTROPODS: INTEGRATING FIELD AND LABORATORY STUDIES

The foraging range of adult snails, Helix aspersa, has beenstudied using radio-transmitters. Snails did not return to anexact roost site after foraging, but often remained in the foodpatch, or returned only to the general roost area. Time lapse video films of the slug Deroceras reticulatum madeunder infra-red lighting in arenas were analysed for tracklengthsand degree of turning, in order to simulate slug movements inan unbounded situation. The results suggest that many food itemsare found by random encounter. Slugs usually ate the first food item found, but often ignoredfood items encountered later. If food was scarce, the slugsfed almost every time. Electronic recordings of bites on a wheatflour pellet over 24 hours show that feeding is most intensein the first two and a half hours from starting to feed, andlater meals are both shorter and less regular. Starved slugsdiffered from fed slugs principally by taking a second mealshortly after the first. When given a choice of a more preferredfood (maize pellets) and a less preferred food (pea pellets)in different ratios, the slugs appeared to encounter pelletsat random, but they fed more from the preferred pellets unlessthe ratio was 1 maize: 7 pea. Starved slugs ate twice as muchas fed ones.     

白垩纪中期缅甸琥珀中陆生腹足类化石的新发现

腹足类化石在地层中丰富且常见,但在琥珀中保存较少。文中描述了产自白垩纪中期缅甸琥珀中的陆生腹足类化石2属2种:Euthema naggsi Yu, Wang and Pan, 2018, Truncatellina dilatatus sp. nov.。这些陆生腹足类新材料的发现,提高了缅甸琥珀中陆生腹足类物种多样性,并进一步印证了白垩纪中期缅甸琥珀森林温暖潮湿的热带雨林环境。     

ADAPTATION FROM RESTRICTED GEOMETRIES: THE SHELL INCLINATION OF TERRESTRIAL GASTROPODS

The adaptations that occur for support and protection can be studied with regard to the optimal structure that balances these objectives with any imposed constraints. The shell inclination of terrestrial gastropods is an appropriate model to address this problem. In this study, we examined how gastropods improve shell angles to well‐balanced ones from geometrically constrained shapes. Our geometric analysis and physical analysis showed that constantly coiled shells are constrained from adopting a well‐balanced angle; the shell angle of such basic shells tends to increase as the spire index (shell height/width) increases, although the optimum angle for stability is 90° for flat shells and 0° for tall shells. Furthermore, we estimated the influences of the geometric rule and the functional demands on actual shells by measuring the shell angles of both resting and active snails. We found that terrestrial gastropods have shell angles that are suited for balance. The growth lines of the shells indicated that this adaptation depends on the deflection of the last whorl: the apertures of flat shells are deflected downward, whereas those of tall shells are deflected upward. Our observations of active snails demonstrated that the animals hold their shells at better balanced angles than inactive snails.     

FEEDING A VOIDANCE OF TERRESTRIAL GASTROPODS TO CONSPECIFIC AND NONSPECIFIC MATERIAL

In laboratory tests the terrestrial gastropods Arion fasciatus,Deroceras reticulatum, Arianta arbustorum and Bradybaena fruticumpreferred control leaf discs over discs treated with an aqueoussuspension of crushed conspecifics. The response to suspensionsof different species was weaker. The strength of the responseincreased with the concentration of the suspension. The suspension'seffect in deterring feeding was inactivated within 18 to 32hours. Hunger reduced normal responsiveness to conspecific fluids;the quality of the control food also affected the response.The results also imply that ranking among individuals is labile.Spraying lettucc with the suspension affected the dispersalof the animals only in early summer. The article discusses thebiological significance of the response and the use of substancesobtained from slugs and snails in the control of pest gastropods. (Received 21 March 1991; accepted 5 September 1991)     

CONVERGENT SHELL MORPHOLOGY IN INTERTIDAL GASTROPODS

The functional morphology of shell infrastructure in 2 speciesof intertidal trochid was compared with that in 2 species ofnerite. The shell of Monodonta constrictais typical of the majorityof trochids. The shell is composed of 4 layers: a distal layer(calcite), anouter prismatic layer (aragonite), a nacreous layer(aragonite), and an oblique prismatic layer (aragonite). Monodontalabio lacks a distal layer and an oblique prismatic layer. Theoblique prismatic layer is replaced by an inner prismatic layerwhich forms an apertural ridge as a result of deposition andresorption. The shells of Nerita versicolor and N. tessellataconsistof 3 layers: an outer prismatic layer (calcite), a crossedlamellar layer (aragonite), and a complex crossed lamellar layer(aragonite). The complex crossed lamellar layer is covered withinclined platelets which superficially resemble the surfaceof the ique prismatic layer of trochids. In addition, the complexcrossed lamellar layer forms an apertural ridge which is similarin appearance to that of Monodonta labio. The outer surfaceof the mantle of Nerita versicolor and N. tessellata is throwninto a series of large folds which lie in contact with the inclinedplatelets of the omplex crossed lamellar layer. The interactionof the mantle folds with the inclined platelets is thought toserve as a rachet mechanism to aid in extension of themantle;a similar function has previously been proposed for trochids.The apertural ridges of Monodonta labio and Nerita are thoughtto prevent excessive desiccation when these gastropodsare exposedat low tide. ¹Contribution No. 56 of the Tallahassee, Sopchoppy & GulfCoast Marine Biological Association (Received 6 July 1979;     

扁担塘螺类生产力的研究Ⅱ、纹沼螺的周年生产量

采用四种方法对扁担塘纹沼螺的周年生产量进行了测算,结果表明,四种方法得到的生产量吻合极好。生产量的去壳干重和带壳湿重分别是体长频度法,178.07mg     

A REVIEW OF POECILOGONY IN GASTROPODS

All alleged cases of poecilogony in marine gastropods, involvingplanktotrophic and non planktotrophic larval development withina single species, are reviewed. It is concluded that there ispresently no known case of poecilogony in prosobranchs and shelledopisthobranchs, although indisputable poecilogony exists inAscoglossa and possibly nudibranchs. The multispiral or paucispiralform of the protoconch, which is a reflecxtion of planktotrophicor non-planktotrophic larval development respectively, can therefore,with a very high degree of confidence, be considered a species-specificcharacter that can be used in routine taxonomical work on bothRecent and fossil material. (Received 29 January 1988; accepted 11 April 1988)     

THE EFFECTS OF MECHANICAL DISTURBANCES ON THE BEHAVIOUR OF INACTIVE TERRESTRIAL SNAILS

Based on comparison to controls, inactive Otala lactea (Mull.)respond to mechanical disturbances such as shaking, percussion,transmitted vibrations, and rotation. Responses in a 15-minperiod include motion of large portions of the mantle, openingof the pneumostome and protrusion of the posterior part of thefoot through the mantle collar. Responses reflect preliminarystages of arousal. It is suggested that an incomplete arousalto a potentially valuable, but environmentally ambiguous stimulus,may be of adaptive value. (Received 30 January 1978;     

INDEPENDENT EVOLUTION OF TERRESTRIALITY IN ATLANTIC TRUNCATELLID GASTROPODS

Phylogenetic analysis of truncatellid gastropods using comparative anatomy and ribosomal RNA sequences shows that terrestrial truncatellids likely evolved three times independently in the Caribbean. The terrestrial subfamily Geomelaniinae, characterized in part by pallial fertilization and uniquely derived features of radula and protoconch, occurs in the Greater Antilles and Cayman Islands. Truncatellinae, with renopericardial fertilization, has several widespread amphibious species and two terrestrial species restricted to Trinidad and Barbados. The species in Barbados may be the most recent animal species to evolve full terrestriality; Barbados emerged above sea level only about one million years ago. By the mid-Cenozoic, truncatellids had traits enabling them to colonize land in appropriate tectonic settings. Parallel trends in character evolution occurred in the terrestrial lineages. In older terrestrial radiations, transitional character states would likely be lost, potentially allowing parallelism to confound phylogenetic analysis of morphological characters.     

BATHYMETRIC PATTERNS OF BODY SIZE IN DEEP-SEA GASTROPODS

The shift to smaller body size in marine invertebrates at the deep-sea threshold and size-depth clines within the deep-sea ecosystem are global biogeographic phenomena that remain poorly understood. We present the first standardized measurements of larval and adult size among ecologically and phylogenetically similar species across a broad and continuous depth range, using the largest family of deep-sea gastropods (the Turridae). Size at all life stages increases significantly with depth from the upper bathyal region to the abyssal plain. These consistent clines may result from selection favoring larger size at greater depths because of its metabolic and competitive advantages. The unusually small size of deep-sea mollusks, in general, may represent an independent evolutionary process that favors invasion by inshore taxa composed of small organisms.     

SEMI-LUNAR AND LUNAR SPAWNING PERIODICITY IN SOME TROPICAL LITTORINID GASTROPODS

Littoraria strigata, Nodilittorina millegrana and N. pyramidalisall spawned regularly in a rock-flanked Malaysian bay in March-June1985, whereas none had spawned there in July-October 1981. N.millegrana showed the least precise timing with some irregularpreponderance during the days between 2d before and 7d afternew or full moon and their associated spring tides. Spawningof N. pyramidalis was more strictly confined to spring tideswith 90% of eggs appearing between 2d before and 5d after newor full moon. There was no apparent difference between alternatespawnings on new and on full moons. L. strigata also spawnedregularly on the spring tides with 89% of eggs appearing between1 and 5 days after new and full moon. In this case, however,full moon spawnings (when spring tides rose highest) yieldedsome 7 times more eggs on average than the weaker spring tidesat new moons. In laboratory aquaria, the three species all released eggs duringboth night and daytime and through periods of both spring andneap tides with no evidence that periodicity persisted in constantconditions. The different degrees of 2-weekly spawning periodicity, togetherwith littorinids which spawn only monthly, may represent a rangeof adaptation to life at increasing shore heights. (Received 26 November 1985;     

CONCENTRATIONS OF METALS (Cu, Pb, Cd, Zn, Ca) IN SIX SPECIES OF BRITISH TERRESTRIAL GASTROPODS NEAR A DISUSED LEAD AND ZINC MINE

Heavy metal concentrations in 6 terrestrial slug species inhabitinga disused Pb/Zn mine site were measured by atomic absorptionspectrophotometry. Differences in metal accumulation patternswere such that the species could be ranked in order of overallmetal accumulation capability: Arion hortensis < Deocerasreticulatum < Milax budapestensis < Arion ater < Derocerascaruanac < Arion subfuscus. Species belonging to the samegenus were widely separated by this simple ranking scheme. Theresults are discussed in the context of inter-species competitionand resource partitioning, and cautionary comments are madeconcerning the utility of slugs as biomonitors of terrestrialheavy metal pollution. (Received 25 November 1987; accepted 2 January 1988)     

ZOOGEOGRAPHY OF SOME TERRESTRIAL MICRO-ARTHROPODA IN ANTARCTICA

1. A review is presented of the information relating to the distribution of free-living terrestrial Cryptostigmata, Prostigmata and Collembola in the south polar region. 2. The Maritime zone, comprising the Antarctic Peninsula and its neighbouring islands, forms a less-clearly definable faunal province than does the Continental zone where generic and specific endemism is high. The Maritime distribution of the micro-arthropods forms no consistent pattern, although in the case of the two groups of mites a distinction can be made between a southern and a northern Maritime fauna. The boundary between these two elements appears to lie between the South Orkneys and the South Sandwich Islands. 3. As far as distribution in the Sub-Antarctic is concerned, all three groups of micro-arthropods show certain general similarities, although in each case particular features can also be distinguished. All three show relatively high specific endemism in the Sub-Antartcic, which sugge:ts that this zone is a faunal province distinct from that of the cold temperate zone to the north and other parts of the Antarctic to the south. It seems equally reasonable to recognize that this province can be subdivided into western and eastern parts, each with its own distinct group of species, although the extent to which this separation is expressed varies from group to group. In all three groups there is an element which is circum-Sub-Antarctic in distribution, but this element is more in evidence in the Collembola than in the mites. From the study of the distribution of endemic species in the Sub-Antarctic it is concluded that the fauna of the eastern part has been isolated from the south temperate zone fauna for longer than it has in the west. 4. In all three groups of micro-arthropods a relic element can be identified, the present distribution of which is consistent with the idea of a former continuous distribution extending across a southern land mass incorporating both the eastern and western parts of the continent, the islands on the Scotia Ridge, and the older Sub-Antarctic islands of South Georgia, Macquarie and, possibly, Kerguelen. In the Cryptostigmata in particular, this relic element, which is represented by members of the Podacaridae, is joined in the Sub-Antarctic and Maritime zones by a penetrant element which probably has invaded the south polar region from the north during the post-Pleistocene period. 5. An alternative hypothesis is also discussed, namely that present distribution patterns of micro-arthropods can be explained solely in terms of post-Pleistocene colonization. It is accepted that limited overseas dispersal could have occurred in recent times, indeed may still be occurring between, for example, the various volcanic islands in the eastern Sub-Antarctic, between the south temperate zone and the Sub-Antarctic, and between the latter and the Maritime zone. However, there is no evidence to suggest that any appreciable amount of long-range dispersal is occurring, on the scale required to support this hypothesis. In addition, there is no evidence that rates of speciation in the south polar region are rapid enough to produce the kind of evolutionary divergence which is implicit in the theory of post-Pleistocene colonization.