Bucaniid gastropods from the upper Ordovician of Baltica, with a discussion of the Bucaniinae

ABSTRACT. Three species of bucaniid gastropods from the upper Ordovician of Norway and Sweden are revised: Euomphalopterus excavatus is redescribed as a species of Phragmolites with very wide umbilici and ornamentation similar to that of Offleya. Three out of five specimens from the original type series of Temnodiscus lindstroemi remain, representing two different species of two different genera. The original species name is restricted to a species of Phragmolites, whereas two specimens are considered conspecific with Megalomphala? carinata sp. nov., although the high carina, the flaring aperture and the laterally compressed whorls seen in this species are unusual for the genus. The gastropod subfamily Bucaniinae of the family Bucaniidae is here considered to comprise nine genera. Placement of Phragmolites in this family is supported by its deep slit, tangential aperture, transverse growth lines, spiral and collabral ornamentation and the presence of a longitudinal keel on the base of the whorl.     

Regulation of spiral growth in planorbid gastropods

Extensive experimentation has been performed on the planorbid Planorbarius metidjensis in order to determine which mechanism allows the snail to coil its shell regularly. Individuals of this species, like all Planorbidae, are permanently active and secrete their shells while crawling on the substrate. Experiments consisted of attaching weights to either side of the shell (which is carried almost vertically) in an umbilical position; these weights cause the shell to fall towards the substrate on the loaded side. It can be demonstrated, qualitatively and quantitatively, that during further growth the shell tube deviated initially (i.e. within the first half whorl after loading) towards the loaded side. In a later stage, when the animal is able to re-balance the shell-load complex by muscular activity, the shell tube gradually deviates away from the loaded side. This behaviour is to be expected if, after loading, secretion of the shell continued with the aperture parallel to the substrate and forming a constant angle with the direction of growth. The main implication is that in normal conditions the living posture largely controls the correct coiling of the shell. Minor experiments made with another planorbid species, Gyraulus laevis , confirm these conclusions. The growth pattern of planorbids requires that the snail has constant information on the orientation of the shell with respect to the substrate. This is permitted by the particular physiological ecology of this group, members of which, unlike terrestrial gastropods, are permanently active.     

A DEVELOPMENTAL CONSTRAINT IN CERION,WITH COMMENTS ON THE DEFINITION AND INTERPRETATION OF CONSTRAINT IN EVOLUTION

Since orthodox evolutionary theory is functionalist, constraints attain their most important positive meaning as channels of change imposed by historical and formal determinants, rather than by immediate natural selection. Since ontogeny is the usual locus of expression for these determinants, developmental constraint is an appropriate, general term. A particular developmental constraint in Cerion, most variable of West Indian land snails, stands out for two reasons: 1) it is simply and inexorably defined as a consequence both of formal principles (coiling of tube about axis) and of historical contingencies in Cerion's invariant allometry of growth; 2) it is pervasive in its influence, underlying major patterns of variation in every Cerion study I have ever undertaken. I refer to this pattern as the “jigsaw constraint.” When whorls are large and final size is limited, adult shells must grow fewer whorls. In Cerion, this obvious fact is promoted from trivial to important because complex allometries impose a substantial set of further consequences for form upon this basic trade-off of whorl size and whorl number. I show that this complex of consequences dominates patterns of natural variation in Cerion at all levels (among shells within samples, between samples in the geographic variation of single species, and between species in multitaxon faunas). It also sets patterns of hybridization between taxa. This paper is primarily a compendium of such examples. It is designed to illustrate the importance of this constraint by the fundamental criterion of relative frequency.     

Morphological investigations of Miliolidae (Foraminifera) from the Upper Permian of the Southern Alps,based on thin sections and stereoscopic X-ray microradiographs

Shallow marine deposits of the Upper Permian and lowermost Triassic in the Southern Alps between Val Adige (Southern Tyrol, northern Italy) in the west and the Karawanken Mountains (northern Yugoslavia) in the east contain abundant miliolid foraminifera of the genusHemigordius Schubert, 1908. These two-chambered Miliolacea show a great diversity of morphotypes due to numerous combinations in the mode of coiling, the shape of the umbonal thickening, the degree of involution, and the dimensions of the test. The spectrum of internal structures ofHemigordius observed in thin-sections is schematized and illustrated in a diagram. Of special interest are irregularly coiled specimens whose complicated mode of coiling is analysed with help of stereomicroradiographs. According to the number of spiral planes, their angles in between and the number of volutions a streptospiral and a glomospiroid type are distinguished. While the streptospiral mode is characterized by a ± regular coiling plan, the glomospiroid type does not show any rules in the succession of the spiral planes and angles. p [Three-dimensional illustrations eludicate the streptospiral and glomospiroid coiling plan of the genusHemigordius. The new developed X-ray microradiographic technique used in our investigation is described in some details.     

Plant quality vs. risk of parasitism: within-plant distribution and performance of the corn leaf aphid, Rhopalosiphum maidis

1 Colonies of the aphid Rhopalosiphum maidis on Johnsongrass, Sorghum halepense, usually occur inside the whorl. The present work assessed the role of two biotic factors, plant quality and parasitism by Lysiphlebus testaceipes, in determining within‐plant distribution and performance of R. maidis. The mean relative growth rate of aphids inside the whorl and on a mature leaf was compared, and the concentration of hydroxamic acids in those tissues determined as an indicator of plant quality. Parasitism effectiveness and parasitoid behaviour were evaluated using three treatments: aphid colonies placed (1) wholly inside the whorl, (2) on the inner and outer surfaces of the whorl, and (3) on a mature leaf. 2 The mean relative growth rate of aphids was lower on the whorl than on the mature leaf, and hydroxamic acid concentration in the whorl was higher than in the mature leaf. 3 The number of parasitized dead aphids (mummies) inside the whorl was considerably lower than in the other two treatments. Mummies were present in 80% of the replicates in the whorl, whereas mummies were present in all replicates of the other treatments. 4 Host location time of the parasitoid was increased on the mature leaf compared with the other treatments. No significant differences in the residence time of the parasitoid in the aphid colony occurred between treatments. 5 Host location time showed a negative correlation, and residence time of the parasitoid a positive correlation with the number of aphids on the outer surface of the whorl.     

Effect of temperature on embryonic development and reproduction of the freshwater snailLymnaea luteola Troshel (Gastropoda), a vector of schistosomiasis

The effect of temperature on embryonic development and reproduction ofLymnaea luteola was studied. This snail did not develop completely and failed to reproduce at 15 °C and 40 °C. The temperature range of 25 °C–35 °C was observed to be optimum for development and reproduction of this snail. The utility of this study in predicting seasonal fluctuations of snail population in nature is discussed.     

Parallel variation among populations in the shell morphology between sympatric native and invasive aquatic snails

A phenotypic response, either plastic or evolved, is often required for successful invasion of novel environments. Populations of the invasive snail Potamopyrgus antipodarum have colonized a wide range of environments in the western U. S. since 1985, but the extent of plastic adjustment and evolved adaptation to local environments is largely unknown. We examined variation in shell morphology among four sites in the Snake River, Idaho, including both still-water and free-flowing river habitats and compared the variation to that of a native snail (Pyrgulopsis robusta) using geometric morphometric techniques. Using Generalized Procrustes analysis, we tested for phenotypic responses by determining (1) whether Po. antipodarum from the four locations differed in shell morphology, and (2) whether these snails exhibited corresponding shell shape variation with sympatric populations of a native snail. Both native and invasive snails exhibited similar variation in shell morphology across three of the four sites. The Canonical Variate assignment test grouped 85 % of both snail species to their rightful sample site. In addition, the Principal Component Analysis displayed similar patterns of shell variation across the four sites, indicating parallel variation in shell shape. For three of the four sites, both the native and invasive snails exhibited differences in shell shape consistent with water flow variation (still-water versus fast free-flowing river). Taken together, these results suggest that the shell shape of the invasive snail has changed either through plasticity or evolution, and that both native and invasive snail populations responded to local environmental conditions in a similar manner.     

Contraction of protoplasm. IV. Cinematographic analysis of the contraction of some peritrichs

The contraction and relaxation of Vorticella difficilis, V. campanula and Carchesium sp. were studied by high speed cinematography. In Vorticella it was shown that coiling of the stalk usually started near the zooid and spread downwards; the point of initiation bore no relation to the position of the stimulating electrodes. Contraction took about 5 msec to complete, and the fully contracted animals were 29 ± 3.9% of their original lengths. The zooids were 66 ± 5.0% and the stalks 14 ± 6.0% of their original lengths (V. difficilis). The shortening of the stalk was mostly in the form of coiling. Measurement of the myoneme length demonstrated that its real shortening was less than 10%. Thus the contraction is virtually isometric, producing a helical deformation of the stalk. As the stalk contracts it takes the form of a steeply pitched helix. This change in shape should produce rotational forces on the zooid (torque). Physical models of similar proportions produced about 1.5 revolutions of torque for similar changes in pitch. However during contraction no turning of the zooid was detected, though rotation did occur after the completion of contraction. In Carchesium the contraction is not so isometric, the myoneme apparently shortening by 20%. While the coiled shape of the contracted Vorticella stalk can be explained by its acentric structures, the stalk of Carchesium is much more symmetrical in cross-section, demonstrating that a high acentricity is not necessary for helical coiling. In all three species there seems to be some separation of the control of zooid and stalk contraction.     

Efficacy of neem pesticides on whorl larva,stem-borer and panicle insect pests of sorghum in Nigeria

Two field trials were conducted from 2003 to 2005 on the effects of neem pesticides on whorl larva, stem-borer and panicle pests of sorghum. In the first trial (2003–2004) the effect of neem seed granules (NSG) and carbofuran (furadan 3G®) inserted into the sorghum whorl at 30, 40 and 50 days after sowing (DAS) were tested on whorl larva, stem borer and grain yield. Results showed that NSG and carbofuran significantly (P ≤ 0.01) reduced whorl larva feeding, leaf puncturing and chaffy panicle, and significantly (P ≤ 0.01) increased grain yield compared with untreated check. In the second trial, (2004–2005), aqueous neem seed extract (ANSE), neem seed oil (NSO) and deltamethrin (Decis 12 EC®) were sprayed at anthesis and grain filling stages. Results also showed that the three pesticides significantly (P ≤ 0.01) reduced insect damage and also significantly (P ≤ 0.01) increased grain yield by 28.3% (deltamethrin), 19.4% (NSO) and 17.9% (ANSE) above the yield of check. It is suggested that neem pesticides may be suitable as alternatives to synthetic pesticides for the management of sorghum whorl larva, stem borers and panicle insect pests in the Nigerian Sudan savannah.     

FLORAL DEVELOPMENT IN OTTAWA AND FLOREX RED CLOVER TRIFOLIUM PRATENSE (PAPILIONOIDEAE: LEGUMINOSAE)

Floral development in Florex and Ottawa cultivars of red clover (Trifolium pratense L.: Leguminosae) was examined by scanning electron microscopy. No differences between the two cultivars were found. The terminal inflorescence is initiated in the axil of the penultimate bract before the final bract is initiated. After initiation of the final bract, the remnant apical dome is transformed to become the least mature part of the inflorescence dome. Subsequent inflorescences are initiated laterally in basipetal sequence. Inflorescence development is zygomorphic. This leads to an unusual pattern of floret initiation, the oldest florets resting basally and proximal to the penultimate bract. Florets develop with zygomorphic symmetry, each whorl of floral organs developing unidirectionally from the abaxial side. Initiation of the adaxial organ of each whorl is delayed until the abaxial organ of the succeeding whorl has been initiated. Thus there is overlapping development of the whorls of organs. The antepetalous stamens arise in close association with their respective petal primordia. As development proceeds, the corolla tube and the staminal tube exhibit basal zonal growth. In the mature flower, above the distal zone of fusion of the keel petals, marginal cells project and interlock, producing a pollination mechanism that can be sprung by the pollinator.     

Live coral cover may provide resilience to damage from the vermetid gastropod Dendropoma maximum by preventing larval settlement

Dendropoma maximum is a vermetid gastropod (a sessile tube-forming snail) commonly associated with living corals throughout shallow-water reefs of the Indo-Pacific. Recent work suggests that, once established, this species can adversely affect growth and survival of corals. Here, we test the hypotheses that disturbances to live coral substrates (e.g., creation of bare patches) facilitate successful larval settlement and subsequent population growth of D. maximum, and conversely, that live coral inhibits D. maximum settlement. In the shallow lagoon of Moorea, French Polynesia, we selected patch reefs where D. maximum was either present or absent (to evaluate potential effects of resident adult conspecifics on recruitment) and established focal quadrats on each reef. In each quadrat, we either experimentally removed 50 % of live coral cover or left the quadrat with 100 % live coral cover. In addition, we deployed units of bare substrate (coral rubble) to each reef. We conducted a census of deployed substrates and quadrats after 6 months and found that D. maximum settled irrespective of resident vermetid populations, and only onto nonliving surfaces (i.e., cleared patches in quadrats, coral rubble, and marine epoxy). In laboratory experiments, we exposed larvae of D. maximum to live coral and found species-specific effects on survival of D. maximum larvae. Porites lobata and Pocillopora sp. killed larvae of D. maximum, Porites rus caused weaker mortality, and Millepora sp. had no effect on larval survival. Collectively, these results suggest that D. maximum requires disturbances that create bare patches to successfully settle onto reefs, and that a high cover of living corals contributes resilience to reefs by limiting settlement opportunities of a species known to reduce coral growth and survival.     

Coiled-sprout in the potato: the effect of various storage and planting conditions

The incidence of coiled-sprout was determined in Scotch and local-grown Arran Pilot and Duke of York seed tubers which had been stored at 10°, 4° and 15° C. and in a farm store with no temperature control. All four tuber types were planted in the field and, in addition, the two types of Duke of York were planted in Perlite at 7°, 10° and 15° C. In the field, and when maintained at 7° and 10° C, the percentage of sprouts coiling and the intensity of coiling was greater in tubers stored at 10° and 15° C. than at 4° C. There was no coiling when the Duke of York tubers were planted at 15° C. In a further experiment tubers were stored at 20° C. in the light and dark and samples were planted monthly for 3 months at temperatures of 7°, 10° and 15° C. During the following 3-month period only light-stored were planted because of the excessive amount of tip-death in the tubers stored in the dark. There was very little coiling in the dark-stored tubers. In the first two plantings of the light-stored tubers there was virtually no coiling of those planted at 15° C. There was some, however, at 7° and 10° C. In subsequent plantings there was more coiling and no effect of planting temperature. Attempts to isolate Verticiculum nubilum from sprouts were successful in only a small percentage of attempts and it was not possible to demonstrate any difference between its distribution on coiled and normal sprouts. It was not possible to induce coiling by infection of sprouts with spores of V. nubilum. Over a wide range of sprout sizes the amount of coiling was a function of sprout size at planting. However, the parts which coiled were those in the apical bud of the sprout at the time of planting and hence contributed only a small amount to the total sprout size. It is likely, therefore, that the correlation between coiling and sprout size reflects the changing metabolism of the elongating regions of sprouts with their increase in length, these regions developing in such a way as to produce a greater tendency to coiling. The internal reactions concerned in these changes, however, are not known.     

Developmental study on the inflorescence and flower of Caldesia grandis Samuel (Alismataceae)

The inflorescence and floral development of Caldesia grandis Samuel is reported for the first time in this paper. The basic units of the large cymo‐thyrsus inflorescence are short panicles that are arranged in a pseudowhorl. Each panicle gives rise spirally to three bract primordia also arranged in a pseudowhorl. The branch primordia arise at the axils of the bracts. Each panicle produces spirally three bract primordia with triradiate symmetry (or in a pseudowhorl) and three floral primordia in the axils of the bract primordia. The apex of the panicle becomes a terminal floral primordium after the initiations of lateral bract primordia and floral primordia. Three sepal primordia are initiated approximately in a single whorl from the floral primordium. Three petal primordia are initiated alternate to the sepal primordia, but their subsequent development is much delayed. The first six stamen primordia are initiated as three pairs in a single whorl and each pair appears to be antipetalous as in other genera of the Alismataceae. The stamen primordia of the second whorl are initiated trimerously and opposite to the petals. Usually, 9–12 stamens are initiated in a flower. There is successive transition between the initiation of stamen and carpel primordia. The six first‐initiated carpel primordia rise simultaneously in a whorl and alternate with the trimerous stamens, but the succeeding ones are initiated in irregular spirals, and there are 15–21 carpels developed in a flower. Petals begin to enlarge and expand when anthers of stamens have differentiated microsporangia. Such features do not occur in C. parnassifolia. In the latter, six stamen primordia are initiated in two whorls of three, carpel primordia are initiated in 1–3 whorls, and there is no delay in the development of petals. C. grandis is thus considered more primitive and C. parnassifolia more derived. C. grandis shares more similarities in features of floral development with Alsma, Echinodorus, Luronium and Sagittaria. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140 , 39–47.     

STEAM教育理念下“线上+线下”混合教学模式初探：以微生物学实验为例

随着信息化手段的不断丰富,新型教育理念结合线上学习平台的新信息化教学模式成为高校课堂的改革新趋势。本次教学改革利用科学(Science)、技术(Technology)、工程(Engineering)、艺术(Art)和数学(Mathematics)多学科融合的超学科教育理念(简称STEAM教育)对教师教学过程进行了整体设计,同时借助“线上+线下”教学平台对学生学习过程进行了全面优化。将原本分散的验证型、操作型实验重新整合串联成以多角度“项目式”任务为主线、以Blackboard线上平台为辅线的自主研究型实验项目。新型教学模式以学生为主体,给学生提供更多自我展示和讨论互动的平台。从学生的课堂表现、知识测验、课后反馈、实验操作及实验报告4个方面对新型模式下的教学效果进行了分析和评价。结果表明,此模式不仅提高了学生在微生物学实验中的学习质量,增强了其学习主观能动性,而且有利于培养和提升学生的问题探究及实践创新能力。这一新型教学模式对其他生物学科实验课程的教学具有一定的借鉴意义。     

Mode of life of the Silurian uncoiled gastropod Semitubina sakoi n. sp. from Japan

Semitubina sakoi n. sp. from the late Silurian of Japan represents the second species of this genus and also the first record of a Silurian gastropod in Japan. The gastropod shells occur in a thin mudstone bed and were found to be encrusted exclusively by corallites of ? Favosites sp. These corallites reveal that encrustation proceeded as the gastropod shells grew. The ecological relationship between the two organisms is considered to be symbiotic. This mode of life allowed the coral to live on a muddy substrate because clear sea water passed over the colony as the gastropod moved along. The gastropod benefited from this relationship by being protected from shell-boring or shell-crushing predators by the encrusting corallite. In Semitubina sakoi the body whorl is separated from the penultimate one by a considerable gap in a later growth stage and S. sakoi has been cited as one of the uncoiled gastropods. The uncoiling of this gastropod results primarily from rapidly increasing whorl translation rate in the latest growth stage. Taking the symbiotic relationship with ? Favosites sp. into consideration, a deposit feeding or benthic scavenging mode of life is suggested for this gastropod.     

The isolation of protoplasts of the fission yeastSchizosaccharomyces byTrichoderma viride and snail enzymes

The formation of protoplasts of the fission yeastsSchizosaccharomyces pombe andSchizosaccharomyces versatilis after the combined application of snail enzymes andTrichoderma viride enzymes in an osmotic stabilizer (0.4m KC1, pH 5.5) was studied by light and electron microscopy. The effect of the enzymes used leads during 30 min to the formation of 100% protoplast population. Using electron microscopy no original walls or wall remnants were detected in the suspension of protoplasts. Protoplasts are viable and in liquid nutrient medium they regenerate cell walls and revert into normal cells. Such a protoplast population may be useful for biochemical study of protoplast metabolism by quantitative methods as well as for the chemical study of regenerating cell walls.     

Geometric and functional constraints on bivalve shell morphology

The range of shell morphologies available to bivalves is constrained by the geometric properties of coiled shells, and by two contrasting functional necessities: positioning the umbones at a distance from each other, to allow an adequate amount of shell gape, and limiting linear growth of the axial shell margin, in order to prevent the ligament from being rapidly stretched beyond its elasticity limits. These necessities are achieved, or circumvented, in one or more of the following ways: (1) evolving a range of inequivalve adaptations, (2) allowing a large amount of interumbonal growth, while simultaneously adopting a ligament that quickly breaks and is continuously replaced during ontogeny, (3) adopting an outward curving ligament which flexes along its entire width, thus effectively placing the actual pivoting axis of the valves dorsally to the axial shell margin, (4) substituting the ligament with diductor muscles, (5) stopping growth before shell coiling reaches half whorl, (6) decreasing the whorl expansion rate throughout ontogeny, (7) orienting the coiling axes of the umbones at an angle to each other and to the hinge axis.     

Field observations on the influence of low water velocities on drifting of Bulinus globosus

The influence of water velocities of less than 30 cm/s on drifting of Bulinus globosus in a natural stream was investigated. It is shown that although a low water velocity does not sweep away adhering snails, it carries away snails releasing their hold and crawling along the water surface in search of new food sources. A low water velocity therefore assists considerably to the spreading of a snail species. Vegetation was found to have a decisive impact on local water velocity conditions by reducing the current and creating protected pockets. Upstream migration was found not to be common among Bulinus globosus. In addition, evidence for snail drifting under natural conditions within well established Schistosoma haematobium transmission sites is presented.     

Impact of Changing Water Levels and Weather on <Emphasis Type="Italic">Oncomelania hupensis hupensis</Emphasis> Populations,the Snail Host of <Emphasis Type="Italic">Schistosoma japonicum</Emphasis>, Downstream of the Three Gorges Dam

Increasing evidence indicates that dams impact riverine ecosystems and human diseases. Poyang Lake, one of the largest schistosomiasis endemic environments in China, will change due to the construction of the Yangtze River Three Gorges Dam. We assess changes in Oncomelania hupensis hupensis, the snail host for Schistosoma japonicum, in response to changing water levels and weather from 1998 to 2002. In the 5 years following the major flooding of Poyang Lake in 1998, seasonal water levels have gradually decreased, concomitant with decreases in mean and variance of fall snail densities. Nonlinear relationships suggest that the highest spring density is associated with current, 2-, and 3-month prior temperatures of 18°, 9.1°, and 5.8°C, while the highest fall density is associated with 2- and 3-month prior water levels of 17 and 18 m, respectively. This suggests that lower, more stable water levels downstream of the dam may result in a reduction in mean fall densities and their variance. However, additional data are needed to determine whether snail populations that are typically destroyed by seasonal floods may live longer in more stable environments created by the dam.     

Scalp hair-whorl orientation of Japanese individuals is random; hence,the trait's distribution is not genetically determined

Because the features of clockwise versus anti-clockwise orientation of hair-whorl coiling developed on a person's scalp is (partially, albeit significantly) correlated with that individual's right- versus left-hand-use preference (i.e., handedness) in the US and British subjects, these traits have been recently suggested to be determined biologically and through a common genetic mechanism. Here I report results of a serendipitously made observation with the Japanese population that helps to scrutinize validity of partial correlation between these attributes and to ascertain whether the underlying gene's frequency variations exist in different gene pools. Surprisingly, the whorl orientation in the Japanese individuals was found to be random, although their handedness variation is similar to that of the US population. Therefore, the whorl orientation trait is not genetically determined in the Japanese population. This result supports the idea that separate decisions must be made during embryogenesis for developing handedness and hair-whorl features at least in Japanese individuals. A recent study found the lack of association between whorl orientation and handedness in the German population, yet previous studies suggested that their scalp hair orientation is genetically determined. Therefore, pronounced genetic variation for the hair-whorl trait exists between individuals of different geographical regions. As hand preference exhibits “complex correlation” with brain hemispheric functional specialization, implications of these findings are discussed here with the goal to define biology of brain hemispheric laterality determination.