Viviparus ater english

Viviparus ater ater (CRISTOFORI & JAN 1832) – Italian river snail

Superfamily: Ampullarioidea (GRAY 1824)

Family: Viviparidae (GRAY 1847)

Subfamily: Viviparinae (GRAY 1847)

Genus: Viviparus (MONTFORT 1810)

Species: Viviparus ater (CRISTOFORI & JAN 1832)

Subspecies: Viviparus ater ater (CRISTOFORI & JAN 1832)

Description:

The dextrous shells of the Italian river snail grow 35 to 50 mm long and 23 to 35 mm wide. The males stay a little smaller and thinner than the females in the same conditions. There are 5.5 to 6 globose whorls with a distinct suture. They increase evenly, starting at the rather flattish apex (in contrast to those of the Danube river snail . The navel is narrow and open. The shell surface shows a fine structure characterized by growth lines. When there are growth pauses, especially in winter, a distinct growth ring forms. The aperture (and thus also the form of the operculum) is teardrop-shaped. The point is even sharper as that of the common river snail . The growth rings of the corneous operculum are concentric to the excentrical nucleus.

The shell is greenish-brown to blackish with three red-brown bands of varying thickness.

Range, Habitat:

Originally, this species was only found south of the Alps:

In lakes and rivers of Upper Italy from Lago Maggiore to the Isonzo (also e.g. in Lago Sebino/Lombardia, Vernio/Toscana, Lago Alserio, Lago d’Iseo, Lago Garda; delta of the Po river, Lago Caldonazzo and Lago Terlago/Trentino), Slovenia (rarely) France (?), Switzerland (known to be living in Lake Geneva since at least 1900/probably native there, comparably long found in Lake Zurich/possibly not native there; also in other lakes of the Swiss Midland).

The species came to Germany (Lake Constance) via Switzerland probably with shipping traffic before 1956. There is one further isolated habitat in Upper Palatinate.

Viviparus ater ater prefers habitats comparable to those of the pointed river snail (Viviparus contectus) (lentic waters or only a weak current, lots of aquaric vegetation), and where the ranges overlap they are also sympatric. In Lake Constance they are said to be found in masses in shallow water areas.

Water parameters:

The Italian river snail tolerates waters poor in calcium (e.g. Lago Maggiore: 3.4 – 3.9 mg CaCO3/l), however, under these conditions their shells show signs of corrosion, and the snails' life spans are shorter than in waters rich in calcium (e.g. Lake Zurich: 8.3 – 14.5 mg CaCO3/l).

Reproduction:

The reproductive biology of the Italian river snail corresponds mostly to that of the common river snail (Viviparus viviparus).

This species reproduces and its embryos develop all year round if the snails do not hibernate. During this time the individual snails copulate about 60 times. Males search actively for sexual partners and go significantly longer ways than the rather passive females.

The females become sexually active with 1.5 to 2 years.

Every female releases an average of 20 young snails individually over the summer, especially in May and June. The young snails' shells have a diameter of 7 to 11 mm. Smaller offspring compensate the presumed disadvantage by a significantly stronger initial growth within a few months.

The offspring's shells are smooth, shiny and have no short hairs. The frontal mantle rim is smooth or has tiny indentations at best.

Special thanks to: Prof. G. Ribi, Zurich University (source).

Life span: 5 to over 10 years in nature.

Food:

The food biology of the Italian river snail is mostly comparable to that of the common river snail

Behavior:

The behavior of the Italian river snail does not differ substantially of that of the common river snail . In Switzerland (Lake Zurich) this species also hibernates, dug into the sediment in deeper parts of the lake. The duration depends on the length of the winter and the size of the snails. Young snails wander from the shallow zones to deeper areas in this lake from September on. They hibernate from November to April.

In Upper Italy this species does not hibernate.

Keeping and socialization in the aquarium:

Probably nearly identical to Danube river snails (Viviparus acerosus).

Additional Information:

The Italian river snail is listed as endangered in the Swiss Red List.

In natural water bodies there might be hybrids with the pointy river snail (Viviparus contectus), even though they have a different number of chromosomes. The exact way this works is currently being examined.

Experiments showed that when both species are present in equal numbers successful matings of female V. contectus with male V. ater occur significantly more often than matings between female V. ater and male V. contectus. However, if V. ater is in the majority (e.g. 90%), the proportion of in-between-species matings rises from around 15 to 73%. In any case, the offspring are less fertile than homozygous snails – hybrids of female V. contectus and male V. ater are nearly sterile.

KELLER & RIBI (1993, s. web links) observed in Lake Zurich that only 10% of the offspring survive until autumn. The vast majority is eaten by various fish species.

In Europe, the following two subspecies have been described:

Viviparus ater gallensteini (KOBELT 1892)

Range:

Slovenia, Croatia.

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Viviparus ater hellenicus (CLESSIN 1879)

Description:

The rather slim shell only grows to 33.5 mm in length. There are up to 4 weakly globose whorls, the suture between them is flattish. Except for fine lateral stria in accordance with the growth lines the shell surface is smooth.

The shell has a medium to dark brown hue and shows three red-brown bands of varying width.

Range:

Greek mainland (e.g. Lake Trihonida/Etolía region).

Additional information:

Some authors treat it like a species in its own right Viviparus hellenicus (WESTERLUND 1886).

Literature:

GLÖER, P. (2002): Süßwassermollusken Nord und Mitteleuropas. Bestimmungsschlüssel, Lebensweise, Verbreitung. In: Die Tierwelt Deutschlands. Conchbooks, Hackenheim. ISBN 3-925919-60-0.

[information about characteristics, range etc. of the nominate form – in German]

GLÖER, P & MEIER-BROOK, C. (2003): Süßwassermollusken. Ein Bestimmungsschlüssel für die Bundesrepublik Deutschland. Deutscher Jugendbund für Naturbeobachtung, Hamburg. ISBN 3-923376-02-2.

[information about characteristics of the nominate form, range map for Germany – in German]

Web links:

Aquarienschnecken-Forum

[Food thread for Viviparus spec. - in German]

Aquarienschnecken-Forum

[photos of a snail releasing offspring – in German]

Aquarienschnecken-Forum

[Photos – German forum]

Fauna Europaea

[European systematics, information about their range]

FISCHER, W.: Checklist to Austrian Mollusks / European Viviparidae.

[Color photos of Viviparus ater ater shells, information about species locations]

FISCHER, W.: Checklist to Austrian Mollusks / European Viviparidae.

[Color photos of Viviparus ater hellenicus shells, information about species locations]

RIBI, G. & PORTER, A. H. (1995): Mating between two hybridizing species, Viviparus ater and V. contextus (Mollusca: Prosobranchia). Elsevier Anim. Behav.Vol. 49 (5), pp. 1389-1398. ISSN 0003-3472.

[about experimental research about hybridization with Viviparus contectus]

SysTax - a Database System for Systematics and Taxonomy

[information about species locations of collection material]

TRÜB, H. & RIBI, G. (1997): High fecundity of hybrids between the sympathric snail species Viviparus ater and V. contectus (Gastropoda: Prosobranchia). Heredity 79 (1997): 418-423.

[about reproduction in general and hybridization with Viviparus contectus]

WIESE, V: (Red.) (2007): Systematische Übersicht der Land- und Süßwassermollusken Nord- und Mitteleuropas.

[Systematics of European molluscs]

This page was actualized on December 29, 2007

Author: schneckli

Translator: Ulrike Bauer


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