Invasive Species Compendium

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Datasheet

Discus rotundatus
(rotund disc)

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Datasheet

Discus rotundatus (rotund disc)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Documented Species
  • Vector of Plant Pest
  • Preferred Scientific Name
  • Discus rotundatus
  • Preferred Common Name
  • rotund disc
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Mollusca
  •       Class: Gastropoda
  •         Subclass: Pulmonata
  • Summary of Invasiveness
  • Discus rotundatus, commonly known as rotund disc, is a small snail with a flattened disc-shaped shell. It one of the most widespread and common snails throughout large parts of Europe. It is frequently introduc...

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Pictures

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PictureTitleCaptionCopyright
Discus rotundatus (rotund disc): live, extended, adult. Found in leaf litter, under hazel (Corylus avellana). Straidkilly NNR, Co. Antrim, Northern Ireland. October, 2015.
TitleAdult
CaptionDiscus rotundatus (rotund disc): live, extended, adult. Found in leaf litter, under hazel (Corylus avellana). Straidkilly NNR, Co. Antrim, Northern Ireland. October, 2015.
Copyright©Roy Anderson-2015
Discus rotundatus (rotund disc): live, extended, adult. Found in leaf litter, under hazel (Corylus avellana). Straidkilly NNR, Co. Antrim, Northern Ireland. October, 2015.
AdultDiscus rotundatus (rotund disc): live, extended, adult. Found in leaf litter, under hazel (Corylus avellana). Straidkilly NNR, Co. Antrim, Northern Ireland. October, 2015.©Roy Anderson-2015
Discus rotundatus (rotund disc): adult shells. This snail is often found living in moist, sheltered placeS, under leaf litter and stones. Origin: Germany, Bavaria, Upper Franconia, Weismain.
TitleShells
CaptionDiscus rotundatus (rotund disc): adult shells. This snail is often found living in moist, sheltered placeS, under leaf litter and stones. Origin: Germany, Bavaria, Upper Franconia, Weismain.
Copyright©Udo Schmidt-2008/via flickr - CC BY-SA 2.0
Discus rotundatus (rotund disc): adult shells. This snail is often found living in moist, sheltered placeS, under leaf litter and stones. Origin: Germany, Bavaria, Upper Franconia, Weismain.
ShellsDiscus rotundatus (rotund disc): adult shells. This snail is often found living in moist, sheltered placeS, under leaf litter and stones. Origin: Germany, Bavaria, Upper Franconia, Weismain.©Udo Schmidt-2008/via flickr - CC BY-SA 2.0

Identity

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Preferred Scientific Name

  • Discus rotundatus (O. F. Müller, 1774)

Preferred Common Name

  • rotund disc

Other Scientific Names

  • Goniodiscus rotundatus Müller, 1774
  • Gonyodiscus abietinus Bourguignat, 1864
  • Gonyodiscus azorica Mousson, 1858
  • Gonyodiscus brocchii Calcara, 1845
  • Gonyodiscus machadoi Milne-Edwards, 1885
  • Gonyodiscus megerlei Mabille, 1865
  • Gonyodiscus radiatus Da Costa, 1778
  • Gonyodiscus rotundatus Müller, 1774
  • Gonyodiscus spelaeus Kobelt, 1907
  • Gonyodiscus supracostatus von Sandberger, 1874
  • Helix abietina Bourguignat, 1864
  • Helix machadoi Milne-Edwards, 1885
  • Helix rotundatus Müller, 1774
  • Patula azorica Mousson, 1858
  • Patula rotundata Müller, 1774

International Common Names

  • English: garden disc snail; rotund disc snail; rounded snail
  • French: bouton commun

Local Common Names

  • Austria: gefleckte diskusschnecke; gefleckte knopfschnecke; gefleckte schüsselschnecke
  • Croatia: sareni dugmetac
  • Germany: gefleckte diskusschnecke; gefleckte knopfschnecke; gefleckte schüsselschnecke

Summary of Invasiveness

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Discus rotundatus, commonly known as rotund disc, is a small snail with a flattened disc-shaped shell. It one of the most widespread and common snails throughout large parts of Europe. It is frequently introduced to other countries and has become established in North America, South Africa, New Zealand and Brazil. In most cases of establishment outside its natural range populations remain restricted to confined colonies. It inhabits a wide range of habitats, including sheltered places in forest and urban areas but also some moist and shady open habitats. Due to a slow rate of dispersal, the species displays overall only a low degree of invasiveness. It is a vector of tobacco mosaic virus although this has not so far been reported to be of significant economic importance.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Mollusca
  •             Class: Gastropoda
  •                 Subclass: Pulmonata
  •                     Order: Stylommatophora
  •                         Suborder: Sigmurethra
  •                             Unknown: Arionoidea
  •                                 Family: Endodontidae
  •                                     Genus: Discus
  •                                         Species: Discus rotundatus

Notes on Taxonomy and Nomenclature

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Discus rotundatus (Müller, 1774) belongs to the subgenus Gonyodiscus, which in some taxonomic revisions has been elevated to genus level. Therefore in some publications the species is referred to as Gonyodiscus rotundatus (Müller, 1774). Several subspecies have been described, with D. rotundatus rotundatus (Müller, 1774) being most widely distributed throughout its native range. The subspecies D. r. omalisma (Fagot, 1879) has been recorded from Spain and France. Discus r. abietina (Bourguignat, 1864) has been described from Algeria but its taxonomic significance remains disputed (Germain, 1930; Kuznik-Kowalska, 2008; Fauna Europaea, 2013).

Description

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D. rotundatus is approximately 2.5 mm in height and ranges in width from 5.5-7.2 mm (White-McLean, 2016). The flattened almost disc-shaped shell is yellowish brown with reddish brown spots or transverse strips at regular intervals. It is flat with 5.5-6 narrow and tightly coiled whorls, coarsely ribbed, and weakly keeled at the periphery. Albino shells are found occasionally. The umbilicus equals 1/3 of the shell diameter or more (Kerney et al., 1979; Welter-Schultes, 2013). In central Europe the animal is bluish on upper side, greyish white on foot below inferior tentacles; in southern Europe it is bluish black (Welter-Schultes, 2013;White-McLean, 2016).

Distribution

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In its native range of west and central Europe, D. rotundatus is one of the commonest and most widespread snails, including in Ireland and Great Britain (National Museums Northern Ireland, 2010; Horsák et al., 2013; Welter-Schultes, 2013). Its native range stretches from Iceland and Ireland in the West towards the eastern Baltic region, Romania and the Ukraine in the East. In the North it inhabits southern Scandinavia and towards the South Portugal, Spain, Italy and the northeastern states of Africa. There are no records of native occurrences in southeast Europe or from northeast Africa. Whether occasional records from its southeastern limits refer to natural occurrences or human-mediated introductions remains open to debate (Örstan, 2003; Štamol, 2010; Štamol et al., 2015).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

TurkeyPresent, few occurrencesIntroducedÖrstan, 2003

Africa

AlgeriaPresentNative Not invasive White-McLean, 2011
South AfricaPresent, few occurrencesbefore 1986IntroducedHerbert, 2010East and West Cape
Spain
-Canary IslandsPresentNative Not invasive Fauna Europaea, 2013
TunisiaPresentNative Not invasive Gireaud, 2007

North America

CanadaPresentbefore 1953IntroducedGrimm et al., 2016
-British ColumbiaPresentbefore 1953IntroducedForsyth, 2004; Forsyth et al., 2016
-New BrunswickPresentIntroducedForsyth et al., 2016
-Newfoundland and LabradorPresentIntroducedNatureServe, 2015; Forsyth et al., 2016
-Nova ScotiaPresentIntroducedNatureServe, 2015; Forsyth et al., 2016
-OntarioPresentbefore 1953IntroducedForsyth et al., 2016; Grimm et al., 2016
-QuebecPresentbefore 2008IntroducedÖrstan, 2012; Forsyth et al., 2016
USAPresent1930sIntroducedPilsbry, 1948; Dundee, 1974
-CaliforniaPresentIntroducedHertz, 1996; Roth and Sadeghian, 2006San Diego
-District of ColumbiaPresentIntroducedSteury and Steury, 2011
-MainePresentIntroducedNatureServe, 2015
-MassachusettsPresent1930sIntroducedPilsbry, 1948
-New JerseyPresentIntroducedNatureServe, 2015
-New YorkPresentIntroducedHotopp and Pearce, 2007
-PennsylvaniaPresentIntroducedNatureServe, 2015
-VermontPresentIntroducedNatureServe, 2015
-WashingtonPresentIntroducedNatureServe, 2015

South America

BrazilPresentIntroducedSalvador et al., 2013Trinidade Island

Europe

AndorraPresentNative Not invasive Fauna Europaea, 2013
AustriaPresentNative Not invasive Kuznik-Kowalska, 1999
BelarusPresentNative Not invasive Fauna Europaea, 2013
BelgiumPresentNative Not invasive Poppe and Poppe, 2016
BulgariaPresent, few occurrencesIntroducedGeorgiev, 2014
CroatiaPresent, few occurrences Not invasive Štamol, 2010; Štamol et al., 2015
Czech RepublicPresentNative Not invasive Horsák et al., 2015
Czechoslovakia (former)PresentNative Not invasive Horsák et al., 2015
DenmarkPresentNative Not invasive Fauna Europaea, 2013; Liggia, 2016
EstoniaPresentNative Not invasive Fauna Europaea, 2013
FinlandPresentIntroducedKerney and Cameron, 1979
FrancePresentNative Not invasive Germain, 1930
-CorsicaPresentNative Not invasive Réal and Réal-Testud, 1988
GermanyPresentNative Not invasive Fauna Europaea, 2013; Liggia, 2016
HungaryPresentNative Not invasive Solymos, 2008
IcelandPresentNative Not invasive Liggia, 2016
IrelandPresentNative Not invasive Anderson, 2005
ItalyPresentNative Not invasive Manganelli et al., 1995; Reitano et al., 2012
LatviaPresentNative Not invasive Fauna Europaea, 2013
LiechtensteinPresentNative Not invasive Turner et al., 1998
LithuaniaPresentNative Not invasive Fauna Europaea, 2013
LuxembourgPresentNative Not invasive Fauna Europaea, 2013
MaltaPresent, few occurrencesIntroducedGiusti et al., 1995
NetherlandsPresentNative Not invasive Fauna Europaea, 2013; Liggia, 2016
NorwayPresentNative Not invasive Kuznik-Kowalska, 1999; Fauna Europaea, 2013
PolandPresentNative Not invasive Kuznik-Kowalska, 1999
PortugalPresentNative Not invasive Nobre, 1913; Nobre, 1941
-AzoresPresentNative Not invasive Fauna Europaea, 2013; Liggia, 2016
-MadeiraRestricted distributionIntroducedSeddon, 2008Anthropophilic
RomaniaPresentNative Not invasive Fauna Europaea, 2013
Russian FederationPresentNative Not invasive Liggia, 2016
-Western SiberiaPresentNative Not invasive Liggia, 2016
SlovakiaPresentNative Not invasive Horsák et al., 2015
SloveniaPresentNative Not invasive Fauna Europaea, 2013
SpainPresentNative Not invasive Fauna Europaea, 2013; Liggia, 2016
-Balearic IslandsPresent Not invasive Altaba, 1996; Beckmann, 2007
SwedenPresentNative Not invasive Fauna Europaea, 2013; Liggia, 2016
SwitzerlandPresentNative Not invasive Turner et al., 1998
UKPresentNative Not invasive Anderson, 2005
-Channel IslandsPresentNative Not invasive Fauna Europaea, 2013
UkrainePresentNative Not invasive Balashov and Gural-Sverlova, 2012

Oceania

New ZealandPresentNative Not invasive Liggia, 2016

History of Introduction and Spread

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The earliest records from the USA are from Massachusetts dating back to the 1930s (Pilsbry, 1948). In Canada the species has been first recorded from Toronto, Ontario in 1953 (Grimm et al., 2016).

Risk of Introduction

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As a soil and leaf litter inhabiting snail, D. rotundatus can easily be accidently introduced via the horticultural and nursery trade. According to US national PPQ statistics the species accounted for 1.08% of all gastropod interception in the USA between 1993 and 1998 (Robinson, 1999). This indicates that risks of accidental introduction are highest when phytosanitary standards fail to intercept snails from shipments within the horticultural trade. There are no indications that the species has been deliberately introduced to new areas in the past.

Habitat

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Originally a woodland species, D. rotundatus also invades anthropogenic habitats such as parks and ruins. It inhabits leaf-litter, being associated with rotting wood (Kuznik-Kowalska, 1999). In central and northwestern Europe, D. rotundatus primarily inhabits sheltered places in forests such as under dead wood logs and stones, litter and damp herbage. It also can be found in all kinds of moderately moist and shady places in open habitats and is often ubiquitous in hedgerows or any kind of man-altered terrain (Kerney et al., 1979; National Museums Northern Ireland, 2010; Welter-Schultes, 2013). The species is common in gardens, particularly among rubbish piles (Kerney et al., 1979; Welter-Schultes, 2013). In southern parts of its range it can be found under stones and disintegrating leaves in humid and shady habitats, in soil litter and at the basis of old walls, often in colonies of numerous individuals (Welter-Schultes, 2013). It is also an extremely common and widespread species in urban habitats in central Europe (Horsák et al., 2013).

In North America, it is largely found in gardens, parks and greenhouses (Herbert, 2010). In Western Cape, South Africa it has spread from suburban gardens into natural vegetation (shaded kloofs) in the Cape Peninsula National Park, whereas in the Eastern Cape it has been found in remote indigenous forests (Herbert, 2010).

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Other
Soil Present, no further details Natural
Terrestrial
Terrestrial – ManagedCultivated / agricultural land Principal habitat Natural
Protected agriculture (e.g. glasshouse production) Secondary/tolerated habitat Natural
Managed forests, plantations and orchards Principal habitat Natural
Urban / peri-urban areas Principal habitat Natural
Terrestrial ‑ Natural / Semi-naturalNatural forests Principal habitat Natural
Land caves Present, no further details Natural
Rocky areas / lava flows Present, no further details Natural

Hosts/Species Affected

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D. rotundatus has not been reported as a pest of crops or other plants. It has, however, been listed as an important vector of the tobacco mosaic virus (Robinson, undated).

Biology and Ecology

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Reproductive Biology

In Europe, the reproductive season ranges from May to October and uniparental reproduction is regular (Kuznik-Kowalska, 1999; Welter-Schultes, 2013). On average eggs measure roughly 1 mm in diameter (ranging from 0.7-1.5 mm) and their size is positively correlated with the size of the parent (Frömming 1954; Kuznik-Kowalska, 1999). Eggs are deposited in clutches (1-15 eggs per clutch) with most often 3-4 eggs being arranged in a characteristic pyramid or in a row 2-3 weeks after copulation (Kuznik-Kowalska, 1999; Welter-Schultes, 2013). The eggs are laid in humid, sheltered places, preferably on a substratum that will later serve as a food source for the hatchlings, e.g. bits of bark, decaying wood or decaying leaves under trees (Kuznik-Kowalska, 1999; Welter-Schultes, 2013). The incubation period ranges from 10-36 days; juveniles hatch initially with 1.5-2.3 whorls, growing at a rate of 0.5 whorls per month. Maturity is reached in the second season at 5.5 whorls (Kuznik-Kowalska, 1999; Welter-Schultes, 2013).

D. rotundatus can reproduce by self-fertilization (R. Cameron, University of Sheffield, UK, personal communication, 2016).

More detailed information on the reproductive biology of D. rotundatus is provided by Kuznik-Kowalska (1999).

Longevity

The life span of D. rotundatus is 2.5-3.5 years (653-1145 days), and the time between the last deposited egg and death is given with 504-551 days (Kuznik-Kowalska, 1999; Welter-Schultes, 2013).

Population Size and Structure

In beech litter D. rotundatus was overserved to be among the dominant snail species reaching densities of > 13 individuals per m2, playing a prominent role with regards to litter ingestion (Mason, 1970). Densities vary between habitats and Kappes et al. (2009) demonstrated that in a wooded environment its density decreased with forest size.

Nutrition

D. rotundatus is primarily a litter feeder mainly ingesting plant debris, humus, algae and fungi. As such is one of the few land snails introduced to Canada not regarded a pest (Grimm et al., 2016). Egg cannibalism has been observed. Juveniles consumed conspecific eggs (both of their own clutch and of different clutches), but rejected eggs of other snail species, including other Discus spp. during multiple choice tests (Kuznik-Kowalska, 1999). There is little evidence that D. rotundatus is feeding extensively on eggs of other snail species (Kuznik-Kowalska, 1999).

Associations

D. rotundatus seems to compete with Discus ruderatus at higher altitutes and at the extreme north and east of its range, and the two species do rarely coexist (Welter-Schultes, 2013).

Environmental Requirements

D. rotundatus is a west and central European species reaching 63°N latitude in Norway and 58°N in Sweden. It also inhabits countries with Mediterranean climate in southwest Europe and northeast Africa. The limitations to its climatic range towards southeast Europe are not clearly known, but it is absent from the Balkan and southern Carpathian countries (Kuznik-Kowalska, 1999).

Its upper altitudinal limits are given at 1,200 m a.s.l. in the Carpathians and Sudetes and 2,550 m a.s.l. in Switzerland (Germain, 1930; Kuznik-Kowalska, 1999). In France it has been recorded from 1,400 (rarely above 1,900) m a.s.l. in Savoie and 1,800-2,000 m a.s.l. in the Pyrenees (Germain, 1930).

D. rotundatus tolerates non-calcareous substrate but is usually rare on nutrient poor (dystrophic) soils and rocks, although it sometimes can be found in lagg woodland around the edges of raised bog and often on agriculturally enriched former peatlands (National Museums Northern Ireland, 2010; Welter-Schultes, 2013).

Climate

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ClimateStatusDescriptionRemark
C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Df - Continental climate, wet all year Tolerated Continental climate, wet all year (Warm average temp. > 10°C, coldest month < 0°C, wet all year)
Ds - Continental climate with dry summer Tolerated Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
63

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Abax parallelepipedus Predator not specific N
Columba oenas Predator not specific N
Cosmocercoides dukae Parasite not specific N
Erinaceus europaeus Predator not specific N
Ficedula hypoleuca Predator not specific N
Melinda caerula Parasite not specific N
Myxophyllum steenstrupi Parasite not specific N
Oxychilus helveticus Predator not specific N
Parus major Predator not specific N
Phasmarhabditis hermaphrodita Parasite not specific N
Pherbellia albocostata Parasite not specific N
Pherbellia dubia Parasite not specific N
Platydemus manokwari Predator not specific N
Rhabditis Parasite not specific N
Sorex araneus Predator not specific N
Sturnus vulgaris Predator not specific N
Tetrahymena rostrata Parasite not specific N
Turdus merula Predator not specific N

Notes on Natural Enemies

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Land snails have many natural predators, including mammals (e.g. hedgehogs or mice) and birds, thrushes in particular, also slow worms and toads. Invertebrate predators include other predatory snails, ground and rove beetles, centipedes, leeches, and flatworms. Also harvestmen of the family Ischyropsalidae are known to be specialised snail predators. However, there a few records of natural enemies referring directly to Discus or more specifically to D. rotundatus.

In Europe, predation of D. rotundatus has been recorded for a range of birds and mammals such as Columba oenas (stock dove), Ficedula hypoleuca (pied flycatcher), Parus major (great tit), Sturnus vulgaris (starling), Turdus merula (blackbird), Erinaceus europaeus (European hedgehog), and Sorex araneus (Eurasian shrew) (Allen, 2004).

The remains of Discus spp. were recorded amongst the gut contents of the ground beetle Abax parallelepipedus (Loreau, 1983), and in captivity D. rotundatus has been observed to be preyed upon by the land snail Oxychilus helveticus (Barker and Efford, 2004). Also in captivity, D. rotundatus is preyed upon by larvae of glow worms belonging to the beetle family Lampyridae (Tyler, 2016).

Parasitic Diptera, particularly of the family Sciomyzidae are frequently specialised to develop in gastropods. In Britain members of this family belonging to the genus Pherbellia (e.g. Pherbellia albocostata) have been recorded to parasitize Discus spp. and Pherbellia dubia specifically D. rotundatus (Bratt et al., 1969; Chandler, 1972; Revier, 1982). Equally, the parasitic fly Melinda caerula (Calliphoridae) is recorded to develop in D. rotundatus (Coupland and Barker, 2004).

In Australia, the flatworm Platydemus manokwari (Rhynchodemidae) preys on the genus Discus (Winsor et al., 2004).

Parasitic nematodes such as Cosmocercoides dukae or Rhabditis spp. have been recorded from the genus Discus (Morand et al., 2004), but only Phasmarhabditis hermaphrodita specifically from D. rotundatus (Morand et al., 2004). In France, infection rates of D. rotundatus by P. hermaphrodita can reach almost 40% (mean number per snail 0.5; ranging from 0-10) (Morand et al., 2004).

The ciliophoran parasites Tetrahymena rostrata and Myxophyllum steenstrupi have been recorded from D. rotundatus (Kazubski, 1958, 1959, 1978; Van As and Basson, 2004).

Means of Movement and Dispersal

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Accidental Introduction

D. rotundatus moves actively only over very short distances and usually remains in confined colonies where it can become abundant (Grimm et al., 2016). It can, however, be easily passively transported over long distances and for this reason Robinson (1999) considered it a travelling species. Supporting the fact that this mode of dispersal is commonly taking place are records of snail interceptions at US ports between 1993-1998, when more than one percent of all specimens intercepted belonged to this species (Robinson, 1999),

D. rotundatus has been found in association with forestry enterprises in remote areas of Eastern Cape, South Africa. The most likely explanation for this is that the snails are present in sylviculture nurseries and that they were translocated to remote forestry plantations in the soil around sapling roots (Herbert, 2010). In cases where plantations are close to indigenous forests, native ecosystems are likely to be invaded by D. rotundatus in the long-term.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Breeding and propagationSylviculture nurseries Yes Herbert, 2010
Cut flower tradeNot explicitly mentioned in literature, but likely based on the species’ biology Yes
DisturbanceNot explicitly mentioned in literature, but likely based on the species’ biology Yes
Escape from confinement or garden escapeNot explicitly mentioned in literature, but likely based on the species’ biology Yes
Flooding and other natural disastersNot explicitly mentioned in literature, but likely based on the species’ biology Yes Yes
ForestrySylviculture nurseries Yes Herbert, 2010
Hedges and windbreaksNot explicitly mentioned in literature, but likely based on the species’ biology Yes
HitchhikerNot explicitly mentioned in literature, but likely based on the species’ biology Yes
Horticulture Yes Robinson, 1999
Landscape improvementNot explicitly mentioned in literature, but likely based on the species’ biology Yes Yes
Nursery tradeSylviculture nurseries Yes Herbert, 2010

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
AircraftNot explicitly mentioned in literature, but likely based on the species’ biology Yes
Plants or parts of plantsNot explicitly mentioned in literature, but likely based on the species’ biology Yes
Soil, sand and gravelNot explicitly mentioned in literature, but likely based on the species’ biology Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bark adults; cysts; eggs; juveniles Yes Pest or symptoms usually visible to the naked eye
Bulbs/Tubers/Corms/Rhizomes adults; cysts; eggs; juveniles Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Growing medium accompanying plants adults; cysts; eggs; juveniles Yes Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Roots adults; cysts; eggs; juveniles Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Wood adults; juveniles Yes Pest or symptoms usually visible to the naked eye
Plant parts not known to carry the pest in trade/transport
Leaves
Stems (above ground)/Shoots/Trunks/Branches

Impact Summary

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CategoryImpact
Economic/livelihood Negative
Environment (generally) Positive and negative

Impact: Economic

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D. rotundatus (Müller) has been recorded as a vector of the tobacco mosaic virus (Robinson, undated; Heinze, 1958), and experiments have shown that when the virus is introduced to mouthparts of Discus snails it can be detected two days later in their digestive system (Borkakati et al., 2009). Details about this potential threat are not known, but it is thought that the economic importance of infection with tobacco mosaic virus through molluscs is small (Heinze, 1958).

Impact: Environmental

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Impact on Biodiversity

In the USA, D. rotundatus has been named as a potential threat to the endemic and endangered native Chittenango ovate amber snail (Novisuccinea chittenangoensis), of which only one extant population is known from Chittenango Falls, New York (Breisch and Niver, 2006; USFWS, 2006). However, there is currently no evidence for D. rotundatus impacting negatively on this species. Recent studies on the biology of D. rotundatus by Kuznik-Kowalska (1999) do not support the idea that the species poses a significant threat.

In Canada D. rotundatus is not regarded a pest as it feeds primarily on litter (Grimm et al., 2016).

Herbert et al. (2010) list the status of D. rotundatus in South Africa as "established, locally invasive" (p.5) but also describes its pest status as "probably a detritivore and of little pest significance" (p. 34).

Risk and Impact Factors

Top of page Invasiveness
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Pioneering in disturbed areas
  • Tolerant of shade
  • Capable of securing and ingesting a wide range of food
  • Benefits from human association (i.e. it is a human commensal)

Detection and Inspection

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It is likely that the most common pathway of further spread of this species will be through shipments of ornamental plants, forest nursery stock and horticultural produce. Another possibility is the spread through shipments of tiles (Herbert, 2010). Whereas adult snails can readily be detected through standard phytosanitary inspection methods, small juvenile stages and eggs are much more difficult to detect.

Prevention and Control

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Control

No specific measures for the control of D. rotundatus have been described.

Biological control

No biological control agents have been assessed or used for the control of D. rotundatus. However, fly larvae belonging to the family of Sciomyzidae parasitize inside aquatic and terrestrial snails and slugs, which could turn individual species into potentially suitable control agents. This has been in particular discussed in the context of a possible control of schistosomiasis and other snail-borne diseases in Africa, South America and the Far East (Smith, 1989).

References

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Allen JA, 2004. Avian and mammalian predators of terrestrial gastropods. In: Natural enemies of terrestrial molluscs [ed. by Barker GM]. Wallingford, UK: CABI Publishing, 1-36. http://www.cabi.org/CABeBooks/default.aspx?site=107&page=45&LoadModule=PDFHier&BookID=209

Altaba CR, 1996. Presence of Discus rotundatus (Gastropoda, Endodontidae) on the island of Mallorca. Miscellania Zoologica, 19(1):51-54.

Anderson R, 2005. An annotated list of the non-marine mollusca of Britain and Ireland. Journal of Conchology, 38(6):607-637.

As JGvan; Basson L, 2004. Ciliophoran (Ciliophora) parasites of terrestrial gastropods. In: Natural enemies of terrestrial molluscs [ed. by Barker GM]. Wallingford, UK: CABI Publishing, 559-578. http://www.cabi.org/cabebooks/ebook/20043115153

Balashov I; Gural-Sverlova N, 2012. An annotated checklist of the terrestrial molluscs of Ukraine. Journal of Conchology, 41(1):91-109.

Barker GM; Efford MG, 2004. Predatory gastropods as natural enemies of terrestrial gastropods and other invertebrates. In: Natural enemies of terrestrial molluscs [ed. by Barker GM]. Wallingford, UK: CABI Publishing, 279-403. http://www.cabi.org/CABeBooks/default.aspx?site=107&page=45&LoadModule=PDFHier&BookID=209

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Terrestrial Mollusc Toolhttp://www.idtools.org/id/mollusc

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26/02/2016 Original text by:

Norbert Maczey, CABI, UK

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