Gastropod shell utilisation pattern by the hermit crab Clibanarius symmetricus (Anomura: Diogenidae) in an Equatorial Amazon estuary

Clibanarius symmetricus is a diogenid hermit crab that is highly abundant in rocky intertidal environments, including the rock outcrops of Amazon estuaries. This study characterises the C. symmetricus shell utilisation pattern in the Marapanim River estuary, Pará, Equatorial Amazon, based on the hypothesis that occupancy patterns would differ, in relation to biometry and diversity of occupied shells, from those of other regions in the range of this species due to the distinct and unique environmental characteristics of equatorial estuaries. Monthly samplings were carried out from August 2006 to July 2007, in the upper and lower areas of the mid-littoral during low tides. A total of seven gastropod species were found as shells occupied by hermit crabs: 93.33% were Thaisella trinitatensis shells, 2.00% Nassarius vibex, 2.00% Neritina virginea, 1.33% Natica marochiensis, 0.67% Parvanachis obesa, and, occasionally, Littorina flava and Phalium granulatum shells, each with only one occurrence (0.33%). Juveniles [cephalothoracic shield length (CL) of less than 3.6 mm] occupied a higher variety of shells, while adults occupied shells with larger meristic variation. Males occupied larger shells. The length of the animal was influenced by shell measurements (total width, aperture width and weight). Clibanarius symmetricus showed occupancy patterns generally similar to those of specimens of the same species previously studied in the Brazilian subtropical region, and this occupancy is explained by shell availability, shell size and weight, and hermit size. However, this study showed lower occupied shell species diversity, and the species with highest occupancy frequency (T. trinitatensis) was not reported in any previous studies on this hermit crab. In addition, the studied population differed in occupancy patterns, with differences between males and females, and between juveniles and adults.     

What is the matter with Corbicula fluminea (Mollusca: Bivalvia: Cyrenidiae)? Occurrence of unusual shell erosion in Northern Italy

ABSTRACT

Corbicula fluminea is a bivalve considered to be among the 100 worst invasive species in Europe due to its economic and ecological impacts in freshwater ecosystems. Here, we report for the first time a phenomenon of shell erosion observed in two distinct populations of C. fluminea collected in 2015 from two semi-natural small streams of the River Ticino hydrographic basin (Northern Italy). We measured several biometric variables in order to quantify the shell damage: length and thickness of the right valve and the shell free dry weight of each specimen and compared results with those of ‘normal’ populations from another stream of the same area. Our results confirmed that there was abnormal shell erosion and a reduction in shell thickness in both populations. We hypothesised several potential causes for the observed erosion, but none of them could provide sufficient explanation: neither the pH of the water, nor the level of calcium or total hardness of the water or granulometry of the substrates differed among streams. Similarly, predation pressure cannot be considered a reasonable explanation, since in the study area only a few animals actively prey on these bivalves and the marks they leave on the shells are completely different from the ones observed on our specimens. Lastly, we hypothesised that the bivalves may have been affected by a disease or parasitic infestation that had weakened their shells or prevented them from self-repairing and identified a fungal parasite that could possibly cause a disease to C. fluminea, namely the Ascomycota Geotrichum candidum. However, this species occurred only in one of the two abnormally eroded populations. In conclusion, a valid explanation for the morphological alteration that our study revealed has yet to be found.     

The reproductive strategies of clausiliid land snails from Northern Vietnam (Gastropoda: Stylommatophora)

Under laboratory conditions we scrutinized the reproduction and development of two clausiliid land snail species from northern Vietnam: Phaedusa paviei (Morlet, 1892) and Oospira vanbuensis (Bavay and Dautzenberg, 1899). These species, very similar in shell size and shape, feature different reproductive modes. The former is viviparous, giving birth to one or two neonates on a single occasion, with the number of developing embryos retained in the reproductive tract ranging from 1 to 11. The embryonic shells are 1.8–4.7 mm in height. The latter species is oviparous and produces eggs in clutches (four to six per clutch). Hatching occurs 18–21 days after egg-laying. Both species exhibit a similar growth pattern: the ultimate shell size is attained after 6.5–8.5 months and reproduction starts 5–7 months later. The distribution of viviparous reproduction among the Phaedusinae and its taxonomic importance are discussed.     

Intraspecific variation in integumental pore signatures in the genus Pleuromamma (Copepoda: Calanoida)

Intraspecific variation in the pore signature of calanoid copepods is evident between individuals within a single geographical area (within-sample variation) and between different geographical area (geographical variation). Previous studies, however, have tended to consider only geographical variation, neglecting within-sample variation; thus the question remains on how representative the data are of biogeographic divergence within a species. Eight species of the metridinid genus Pleuromamma are examined and the extent of intraspecific variation in pore signatures is assessed here in terms of within-sample variation. In general, the degree of intraspecific variation increases with increasing number of the total integumental pores and is limited to 10% or less of the total. Intraspecific variation reflects not only genetic variability within a species but also genetic similarities between the species within a genus. This paper also re-examines published data on intraspecific variation in pore signatures. Samples as small as five individuals will identify >95% of potential sites of pores.     

Patterns of prey use in four sympatric species of Philanthus (Hymenoptera: Sphecidae) with a review of prey selection in the genus

Summary

Observations were made on four sympatric species of sphecid wasps of the genus Philanthus that nest in late summer and prey upon Hymenoptera. All four species nest in a restricted locale, but with little overlap in nesting areas. Comparison of nest contents of females demonstrated limited overlap in prey utilization among the four species, but only when both size and taxonomic category of prey were considered. The ultimate cause of this resource partitioning is unknown. Review of 30 populations of 16 species of North American Philanthus reveals varying degrees of specialization on prey types. Although populations of one species, separated in either time or space, tend to have similar niche breadths, this is not always the case. Intra-and inter-populational comparisons of prey records suggest behavioural plasticity allowing response to variations in prey availability. Some of the divergence in prey use among species is due to differences in predator size.     

Pattern of shell occupation by the hermit crab Pagurus exilis (Anomura,Paguridae) on the northern coast of São Paulo State,Brazil

The purpose of this study was to determine the shell occupation pattern of Pagurus exilis using the percentage of shell types that were occupied and the morphometric relationship between hermits and occupied shells. Specimens were collected monthly from July 2001 to June 2003. A total of 1737 individuals were collected, occupying 19 gastropod shell species. Buccinanops gradatum (82%) was the most occupied shell, followed by Natica isabelleana (6.4%), Stramonita haemastoma (3.2%), and Cymatium parthenopeum (2.2%). There was a differential shell utilization pattern between sexes; males occupied larger and heavier shells while the non‐ovigerous females occupied the lightest ones. Pagurus exilis occupied more bare shells instead of incrusted ones. Buccinanops gradatum was the most occupied shell species as a function of its availability in the survey, and this occupation is strongly associated with the higher internal volume presented by these shells.     

Needle biomass equations for singleleaf pinyon on the Virginia Range, Nevada

Foliar biomass of singleleaf pinyon ( Pinus monophylla Torr. & Frem.) was estimated on the Virginia Mountains, Nevada, based on the easily measured dimensions of crown volume and sapwood area. Leaf biomass estimation techniques used in other studies of pinyon where total leaf biomass was collected were supported. Both sapwood area (cm 2 ) and crown volume, calculated as one-half of an ellipsoid (m 3 ), were found to be significantly related to total dry weight needle mass (g). Best predictive equations for crown volume were obtained with nonlinear regression analysis. A previously reported two-part relationship based on tree size for predicting needle biomass with sapwood area was supported. Foliar biomass of singleleaf pinyon can be accurately estimated with a minimum of 10 sapwood cores.     

The first record of the genus Vejdovskybathynella Serban and Leclerc, 1984 (Syncarida,Bathynellacea, Bathynellidae) in the Iberian Peninsula: three new species

Three new species of the genus Vejdovskybathynella are described from caves in northern Spain. It is the first time that this genus has been documented in the Iberian Peninsula. Vejdovskybathynella edelweiss n. sp. has several unique features: the setal formula of the antenna (0/2+exp/2+0/1+0/0+0/2+2/4); the form of the segments and claws of the mandibular palp of the mandible of the male; exopod of the female thoracopod VIII similar in size to the endopod (exopod is always longer than the endopod); small frontal projection of the basipod of the male thoracopod VIII, large or very large is common; the form and size of the lobes of the male thoracopod VIII is unique; the second spine of the furcal rami 2.5 times longer than the first spine. Vejdovskybathynella caroloi n. sp. has a unique male thoracopod VIII with a spur in the exopod that is a feature unknown in the genus, and additionally, this species has the smallest endopod of the thoracopod VIII male of the entire genus; the presence of three aesthetascs in segments VI and VII of the antennule had not been observed in this genus until now; the form of the segments of the mandibular palp of the mandible of the male are unique; the distal spine of the sympod of the uropod is larger than in other species, whereas in the rest of the species of the genus they are equal in size. Vejdovskybathynella pascalis n. sp. is the smallest species of the genus and has two and three aesthetascs in segments VI and VII of the antennule, respectively; it is the only species of the genus that has one seta on segment I and two setae on segment IV of the antenna; it has a unique male thoracopod VIII with a small spur on the frontal projection of the basipod and with the endopod larger than all other species in spite of its small size; the basal spine of the sympod of the uropod is smaller than the other three.     

On the taxonomic status of the highly endangered Ponto-Caspian gastropod genus Caspia (Gastropoda: Hydrobiidae: Caspiinae)

Caspia is an endemic Ponto-Caspian Basin genus of hydrobiid gastropods. Around a dozen nominal species of Caspia have been described to inhabit the Caspian Sea while four species occupy a restricted zone in the lower part of the rivers flowing into the Black Sea and the Sea of Azov. Scanning electron microscopic study of the protoconch and radula morphology of two Caspia species from the Azov–Black Sea Basin allows re-evaluation of the taxonomic rank and attribution of the genus. The adult shell geometry and characters of ornamentation do not enable clear demarcation of these species of Caspia but the protoconch parameters do allow their differentiation. Available morphological data on Caspia and the related genus Caspiohydrobia are interpreted here as confirmation of the subfamilial rank of Caspiinae in the family Hydrobiidae, in contrast to the previous affiliation of this group with Pyrgulidae.     

Australian thrips of the Haplothrips lineage (Insecta: Thysanoptera)

Keys are presented to the 11 genera and 50 species, including 21 new species, of Thysanoptera in Australia that are related to the worldwide genus Haplothrips Amyot and Serville. These taxa belong to what, in recent literature, has been called the “Haplothrips‐lineage”, that is, one of the three major radiations among the 2700 species and 350 genera of Thysanoptera Phlaeothripinae. The group is redefined, and the available tribal name Haplothripini shown to be appropriate. The character states on which the definition is based are discussed, and a list given of the 34 genera worldwide that can be included. The Australian species in these genera exhibit a diversity of biologies. Three genera involve species that invade galls induced by other thrips: Androthrips monsterae (Moulton) from New Guinea is newly recorded from Australia; Mesothrips jordani Zimmermann from South‐East Asia is newly recorded from Australia, with two new synonyms; the Asia‐Pacific genus, Euoplothrips Hood, includes two species in northern Australia. Three haplothripine genera are associated with grasses: one widespread genus, Apterygothrips Priesner, considered polyphyletic, includes only one Australian species; the only known species of Dyothrips Kudo is Oriental but extends into tropical Australia; Podothrips Hood, a circum‐tropical genus of thrips predatory on grass‐living coccoids, has 11 Australian species, six newly described. One grass‐associated genus, Bamboosiella Ananthakrishnan, is excluded from the Haplothripini. An Oriental genus of leaf‐ and flower‐living species, Dolichothrips Karny, includes one species in northern Australia, D. reuteri (Karny); Membrothrips Bhatti in which this species has been placed is considered a synonym. Karnyothrips Watson includes two species introduced to Australia, both predators of coccoids. Priesneria Bagnall includes three species from Australia, of which one fungus‐feeding species is newly described. Xylaplothrips Priesner is a widespread but ill‐defined, polyphyletic genus that currently includes three little‐known Australian species. Haplothrips is the main focus of this study, and character state variation among the Australian species is discussed. In total 24 species of Haplothrips from Australia are recognised, 14 being new species. Also included are the following, one new generic synonym, four new species synonyms, and one new combination. The 250 species worldwide in the genus are usually associated with the flowers of Asteraceae and Poaceae. In Australia, several of the species are specific to flowers, particularly of Poaceae and Cyperaceae but not Asteraceae. Almost half of these Australian species are presumed to be predatory on other small arthropods, and two have unusual host associations—with salt marsh Chenopodiaceae, and with the sori of Dicksonia tree ferns.     

Revision of the genus Caucasocressa from the eastern Pontic Region (Gastropoda: Hygromiidae)

The genus Caucasocressa is revised. Ten Caucasocressa species are known from north-east Turkey and south-west Georgia. Five new species are described. For every taxon the shell is described and illustrated and the variability of the genitalia (as far as known) is shown. All synonyms are listed. The distribution is summarized and all locality records are listed. The distribution of the species is illustrated on a UTM grid-map.     

Morphometrical characterization of the Austropotamobius pallipes species complex

Genetic studies have shown that the threatened crayfish Austropotamobius pallipes species complex is composed of two lineages (A. italicus and A. pallipes), both occurring in Italy. However, the issue surrounding their taxonomic status has not yet been solved even though the confused taxonomy may hamper attempts to conserve indigenous crayfish. The aim of this study was to develop methods for the morphometrical characterization of the A. pallipes species complex. Having analysed 18 morphometric variables on a total of 44 specimens of each lineage, we showed that the tip of the rostrum could be used to discriminate A. italicus and A. pallipes. Such discrimination was also obtained by analysing the size and shape of both the female spermatophoric plate and the male gonopods. These results confirm the potential to adopt morphometric studies to complement the genetic characterization of cryptic species.     

On morphological and ecological evidence of adaptive differentiation among stony cliff littoral Baikal gastropods

Three morpho- or ecotypes (‘ribbed’, ‘middle’ or ‘ribless’ shell and ‘smooth’) of lithophilous Maackia herderiana (Lindholm, 1909) (Caenogastropoda: Baicaliidae) were investigated along the hydrodynamic zones of four locations on the southwestern littoral of Lake Baikal in southeast Siberia. We found a prevalence of the ribbed-shell morphotype inhabiting stones at a depth of 1.2–2.0 m, corresponding to the hydrodynamic zone of strong wave activity, and a predominance of the smooth-shell morphotype living on cliffy canyons at 21–31 m depth in the hydrodynamic zone where wave action is very weak or totally absent. Mixed groups of snails with ribbed, ribless and/or smooth shells were present on stony-boulder substrates at 3 to 15–19 m depth of the wave-cut and wave-weakening hydrodynamic zones. Ribbed-morphotype snails living in inshore and wave-cut hydrodynamic zones had a smaller shell size than did smooth-morphotype snails inhabiting zones where wave activity was weak or totally absent. The thickness of ribbed shells in the non-ribbed areas was equal to the thickness of smooth shells; ribs enhance the thickness of the shell by 3–4 times, thereby increasing the strength of ribbed shells against destructive wave action. On the basis of the different correlation coefficients of shell weight, soft body mass and total mass with increasing shell height, we assumed a growth differentiation between the ribbed and smooth morphotypes. We compared our results with data on ecotypes of some freshwater and marine gastropods.     

Estimation procedures for understory biomass and fuel loads in sagebrush steppe invaded by woodlands

Regression equations were developed to predict biomass for 9 shrubs, 9 grasses, and 10 forbs that generally dominate sagebrush ecosystems in central Nevada. Independent variables included percent cover, average height, and plant volume. We explored 2 ellipsoid volumes: one with maximum plant height and 2 crown diameters and another with live crown height and 2 crown diameters. Dependent variables were total, live, leaf, and dead biomass. Simple, multiple, linear, and power equations were investigated. Models were chosen based on scatter plots, residual plots, and R 2 and SEE values. In general, simple power equations provided the best-fit regressions. For shrubs, the ellipsoid volume computed with maximum plant height best predicted total plant weight, and the ellipsoid volume computed with the live crown height best predicted shrub foliage weight. In addition to regression equations for biomass, ratios for division of that biomass into 1-, 10-, 100-, and 1000-hour fuels were derived for common large shrubs. Regression equations were also derived to relate litter mat sizes of major shrub species to litter weights. The equations in this paper could be used to predict biomass in other areas of the Great Basin if training data were taken to validate or adjust these models.     

Three new endogean species of Laparocerus Schönherr, 1834 from the Canary Islands (Coleoptera,Curculionidae)

Three new species of the weevil genus Laparocerus Schönherr (1834) adapted to the edaphic environment of the Canary Islands are described: L. edaphicus n. sp., L. oromii n. sp. and L. lopezi n. sp. They live in the humid laurel forests of Tenerife (Anaga Mountains), La Gomera (Garajonay National Park) and Gran Canaria (Valsendero), respectively. The small size and somewhat tubular body shape is a common character among them, as is the reduction of the eyes, which are totally absent in L. oromii n. sp. Despite these common adaptive traits, the three species seem not to be directly related. A key for the identification of all the known cryptozoic (edaphic and troglobitic) species of Laparocerus is provided.     

On a new species of centipede (Chilopoda,Geophilomorpha) from the Isles of Scilly

Several specimens of a small geophilomorph centipede were collected by the author from the Isles of Scilly between 1984 and 1987. The last legs bear a tuberculate pretarsus which is a diagnostic character of the North American genus Arenophilus but this species is not among those listed in Crabill's (1969) review of that genus.     

Symbiotic associations between hermit crabs and bryozoans from the Otago region,southeastern New Zealand

Thirteen species of bryozoans (six cyclostomes and seven cheilostomes) occurring off the Otago Peninsula (southeastern New Zealand) form symbiotic, possibly mutualistic, associations with hermit crabs. For all but one of these bryozoan species, such an association has not been reported previously. At most only 3 of the 13 bryozoans are obligate symbionts of hermit crabs. Associations are apparently initiated when a bryozoan larva settles on a gastropod shell occupied by a juvenile hermit crab and develops to form a colony which encrusts the whole shell and then continues to grow out beyond the shell aperture in the form of a helicospiral tube. The tube-building bryozoan colony grows in step with the crab, and tube development appears to be controlled by crab morphology and activity. Of the six species of hermit crabs found occupying bryozoan tubes, four were regular tube occupants, although they could also be found in other shelter types. Hermit crabs occupying bryozoan tubes very rarely indulged in shell exchanges or shell fights. There appear to be no clear cut pairwise correlations between hermit crab species and tube-forming bryozoan species. The following bryozoan species are described for the first time: Heteropora parapelliculata, Borgiola otagoensis, Disporella gordoni, Osthimosia monilifera and O. socialis.     

Shell condition and adequacy of three sympatric intertidal hermit crab populations

Shell use in relation to size adequacy and presence of physical damage and encrustation was evaluated and compared among and within three co-existing species of intertidal hermit crab (Clibanarius antillensis, C. sclopetarius and C. vittatus) in the intertidal region of Pernambuco Islet, São Sebastião Channel, south-eastern Brazil. Comparisons of shell utilization patterns among species and sexes were made with respect to physical damage (perforations and breakage in aperture and apex), encrustation by other organisms and shell size adequacy. Two adequacy indices were calculated. The visual adequacy index (VAI) was based on the degree of hermit crab retraction into the shells (1 = crab totally retracted and 6 = shield exposed). The shell adequacy index (SAI) was calculated through a comparison of the weight of the used versus the preferred shell. A relationship was found between VAI and SAI with crabs assigned as VAI = 3 occupying optimal shells (SAI = 1), i.e. crabs that could retract and those that could not retract the whole body into shells were in relatively heavier and lighter shells than the preferred ones, respectively. Shells utilized by the hermit crabs were generally undamaged and highly encrusted (except for C. antillensis) by oysters, barnacles and green algae, features that may reduce the risks of desiccation and predation. The frequent damage to the shell apertures was associated with a high abundance of shell-crushing predators in the studied area. The degree of encrustation as well as the shell adequacy (VAI and SAI) showed intra- and interspecific variation, while the presence of damage differed only among sexes (reproductive classes). In general, the smallest individuals in the populations used relatively heavier shells. Fecundity of the crabs of this assemblage is thought not to be limited by shell use once ovigerous females are occupying optimal shells.     

A new species of Plagiodontes from Argentina,and new data on the anatomy of four other species in the genus (Gastropoda: Orthalicidae,Odontostominae)

Abstract

Plagiodontes weyrauchi sp. nov. is among the smallest species in the genus Plagiodontes (Doering, 1877). Statistical multivariate analyses confirmed its distinctiveness from other species, mostly because of its high number of whorls (8–9.75), relatively small width, and low proportions of last whorl and aperture length to shell length; multivariate discriminant analysis applied to this species and its most similar relative, P. multiplicatus parvus, correctly identified 100%?of specimens. Pallial and genital anatomy supports P. weyrauchi as a different species, mainly because of the position of the ureteric pore, the small general size of the genital system, the presence of an accessory lobe alongside the verge, and the vaginal internal structure. Internal anatomy of four other small-sized taxa in the genus was studied. Two of them have a verge with no accessory lobe [P. dentatus (Wood, 1828) and P. patagonicus (d'Orbigny, 1835)], while the remaining two have an accessory lobe with different characteristics [P. rocae Doering, 1881 and P. multiplicatus parvus (Hylton-Scott, 1952 Hylton-Scott, M I. 1952. Nuevos moluscos terrestres del norte argentino. Acta Zool Lilloana., 10: 5–29.  [Google Scholar])]. Internal structure of the vagina also shows specific differences among Plagiodontes species; their phylogenetic significance will be further investigated.