Redescription of Viviparus sphaeridius Bourguignat 1880 with an identification key of the European Viviparus species ( Gastropoda : Viviparidae )

Dilian Georgiev found topotypes of Viviparus sphaeridius Bourguignat, 1880, which has not been mentioned in the West European literature since its original description, except one citation by Westerlund (1886: 7). The rediscovery of this species is provided. As a result, V. sphaeridius is considered to represent a species in its own rights well distinguishable from the other European species in the genus Viviparus. Additionally, a key to the Viviparus species from Europe is given to facilitate future identification and prevent further misidentifications.

Before 1959 the names V. contectus and V. viviparus have been partly used in reverse sense (e.g.Zilch 1955: V. contectus = V. viviparus, V. viviparus = V. fasciatus), thus many old citations in the literature cannot be trusted (Glöer 2002).On the other hand there are many misidentifications because species of the genus Viviparus are not easy to identify.Falniowski et al. (1996aFalniowski et al. ( , 1996bFalniowski et al. ( , 1997Falniowski et al. ( , 1998) ) examined the morphological and anatomical characters of the European Viviparus spp.and discussed the taxonomical status as well as the phylogeny and could show that all species have a wide morphological plasticity and thus it is hard to identify the species.
Only Viviparus viviparus can be easily distinguished by the blunt apex from all the other Viviparus spp.which have an acute apex, a feature which can be tested with the fingertip (Glöer 2002).From Russia many more Viviparus spp.are listed, especially Viviparus sphaeridius (Bourguignat, 1880) (Starobogatov et al. 2004, Kantor et al. 2009).The identity of V. sphaeridius mentioned by Starobogatov 2004 (p. 267, pl. 95.2) could only be compared by the drawing and the given distribution range by Kantor et al. (2009: "rivers and lakes of the basins of Danube, Dnieper and Dniester rivers ..."), both coincides with our findings.

Research Article
In the Danube near Marten, Bulgaria, Dilian Georgiev found topotypes of Viviparus sphaeridius Bourguignat, 1880 a Viviparus sp.different from the other Viviparus spp.known from this region.This paper is intended to redescribe this species and to expand the knowledge of the mollusk fauna of Bulgaria and the Danubian region.

Material and Methods
The living snails were collected by sieve and preserved in 75% ethanol.The measurements were carried out by using a stereo microscope (Zeiss) with an eye-piece micrometer, the photographs were made with a Leica digital camera system.Voucher material is stored in the Zoological Museum Hamburg (ZMH) and in the collections of the authors.

Results
Unfortunately, Bourguignat does not mention a locality in his original description.In his oeuvres publication from 1891 in the register (p.254), he mentioned the locality "Valachie" for sphaeridia; going to the collection, MHNG 4861 is recorded from "Giurgewo", and thus from what at his time could be considered the "Valachie".The collection houses two other lots under this name, i.e.MHNG 4743 and MHNG 4744, these two lots, however, come from the Uluabat Gölü and the Sapanca Gölü in Turkey.For this reason, they are not considered to be type specimens, because they do not come from "Valachie".It is for this reason that the type locality can be restricted to "Giurgewo" (=Giurgiu, Romania).Because the recent sampling site Marten is opposite to Giurgiu the collected Viviparus sphaeridius can be accepted as topotypes (Fig. 1).
Bourguignat's original description (Fig. 2) and the syntypes, which are housed in the Bourguignat collection in the Muséum d'histoire naturelle de Genève MNHG (Fig. 3A), revealed, that the newly collected specimens of Viviparus belong to V. sphaeridius.We here compared this species with all other European Viviparus spp.known so far and found that V. sphaeridius is distinct from all other species.Redescription: Shell oval conical, thick and yellowish brown (Fig 3B) with three brownish bands (Fig. 3E), not visible in the adults.The 5-6 whorls are slightly convex with a flat suture and an acute apex (Fig. 3D,  3E).The body whorl is very bulbous, the umbilicus is scarcely visible.The first two whorls are very small in height, the others are regularly fast growing.Spire height about a fifth of shell height.Shell height 24-28 mm, width 18-20 mm.Differentiating features: V. sphaeridius belongs to the smaller Viviparus spp. of Europe, together with V. viparus and V. hellenicus (Fig. 4).Independent of the shell height it can be distinguished by the acute apex from V. viviparus which has a blunt apex.It differs from V. hellenicus in the form of the body whorl, which is canted in this species while the body whorl in V. sphaeridius is rounded.From V. acerosus, which also occurs in this region it can be distinguished by the first whorls, which are more flattened in V. sphaeridius and less convex than in V. acerosus.In addition the spire is less higher than in V. acerosus.

Identification of European Viviparus species
While in females both tentacles are acute, in males the right tentacle is transformed to function as a penis.At a first glance the differences between the European Viviparus spp.seem to be very scarce.To distinguish between the Viviparus species it is better to compare the juveniles.The apex of V. viviparus is obtuse (Fig. 5D), the others are acute (Fig. 5).The juvenile shells of V. ater and V. hellenicus are canted, the others are rounded.The suture of the first whorls of V. sphaeridius are small with a flat suture and the spire is only about a fifth of the shell height.Body whorl of juveniles slightly canted, embryonic shells without or with very small hairs V. ater 5' Body whorls of juveniles rounded, embryonic shell with hairs 6 6 First whorls flat, and slightly flattened at the suture V. mamillatus 6' Whorls not flattened at the suture V. acerosus

Discussion
When Bourguignat 1870 described Vivipara danubialis, V. amblya, and V. microlena from the same sampling site, Ibraïla (= Braila, Romania), later on in 1880 he added descriptions of V. letourneuxi, V. taciti, and V. sphaeridia, from Giurgewo (= Giurgiu, Romania).Westerlund (1886: 11) believes that the Vivipara microlena is a female of V. amblya.The other species: V. danubialis and V. sphaeridia were considered by him to be juveniles of V. acerosus Westerlund (1886: p. 7).However, none of the syntypes illustrated in Fig. 6 corresponds to Viviparus acerosus.Probably, the species A-D in Fig. 6 are conspecific and represent another distinct species that needs to bear the name V. danubialis Bourguignat, 1870.Next to this species, V. taciti (Fig. 6F) likewise seems to be distinct from V. acerosus and V. sphaeridius as well.At the moment, not enough specimens are available from the area to resolve this problem.
Unfortunately DG could not find V. acerosus at the same sampling site but Angelov (2000: 5) listed this species as being distributed "mainly in the Lower Danube" and thus, however, it is possible that both species, V. acerosus and V. sphaeridius live sympatrically in this Danubian region.