New helicid in Slovakia

Tomáš Čejka & Juraj Čačaný

The Thessalian snail (Helix thessalica) is one of the newest arrivals of the Slovak and Czech molluscan fauna. The Slovak species name "prehliadaný" (overlooked) suggests that despite its size, this snail has been overlooked and has escaped attention because it has not been distinguished from the very similar and quite common Roman snail (Helix pomatia). Only molecular phylogenetic analyses made it possible to distinguish it from the common garden snail, but in the end, it turned out that it could be well distinguished from the Roman snail by identifying characters on the shell or genitalia.

The Thessalian snail lives mainly in the southwest of the Balkan Peninsula, but along the Carpathian Mountains, its range extends into Slovakia and Moravia. In Slovakia, its range is concentrated in the higher altitudes of central Slovakia (see map below). These are mainly around the municipalities of Zvolen, Rimavská Sobota, Muráň, Liptovský Hrádek and Brezno. An attractive locality is, e.g. the surroundings of the Čiernohronská forest railway; other records come, e.g. from the Ohnište locality in the Low Tatras or the Nemecká locality, where the species lives along the stream near the Slovak National Uprising memorial.

How to distinguish Helix thessalica from H. pomatia

Distinguishing between the two species is difficult and requires previous experience in identifying gastropods. In fact, the best features of a shell are its overall shape, colour and surface texture. The differences are rather subtle, difficult to grasp and, above all, variable, although the agreement with molecular data confirms their reliability. The shell of the overlooked snail is overall more spherical and sort of neat in shape (Fig. 1), has a shallower suture and a relatively larger mouth that has a straight edge or is only slightly curved outward. The basic colouration of the shell is distinguished by the shade of brown, which is more ochre and may be slightly greenish in certain lighting. Most populations have developed four longitudinal bands. These are characterised by their arrangement with two broader bands in the middle and two fainter ones on the sides of the whorls, but they may also be absent; moreover, a similar banding pattern is also found in the garden snail.

Fig. 1. Colour and shape variation in the shells of Helix pomatia (left) and H. thessalica (right).

An important feature is the granular structure of the shell surface (Fig. 2). The surface organic layer (conchine) in place of the small granules is already peeling off during the snail's life so that the shell acquires a typically abraded appearance relatively early.

The Roman snail has porcelain-whitish genitalia; rarely, the penis may be greyish. Helix thessalica has the penis, vagina and other distal parts of the genitalia dark grey (Fig. 3). Czech and Slovak's populations usually differ from the garden snail by the darker colour of the legs, which are also grey.

Fig. 3. The Helix thessalica can be easily distinguished from the garden snail by the dark-coloured distal parts of the genitalia. PE -penis, PŽ - finger glands, SP - spermoviduct, ŠV - arrow sac, TY - right tentacle, VA - vagina, VO - oropharynx, VY - reptaculum seminis. The garden snail has its entire genitalia coloured approximately like the spermoviduct in the top picture. Photo O. Korábek

Assistance with mapping

Because of the little-known distribution in Slovakia, we ask the professional and general public for help in mapping this species. We would especially welcome live specimens. It is a good idea to put the collected specimens in a cloth bag, old silk stockings are also excellent. It is necessary to enclose a locality label (placed in a small plastic bag so that the snails do not eat it) on which the nearest municipality is indicated, ideally with the WGS coordinates, the date of collection and the name of the collector, or other details about the locality (habitat type, habitat). Put the snails in a cool place (fridge, cellar, etc.), if possible rather dry, so that they are not active. Access to air is necessary. Snails can last for several weeks without special care.
Send suspiciously coloured snails to the address below.

Pomoc pri mapovaní

S ohľadom na málo známe rozšírenie na Slovensku, prosíme odbornú aj laickú verejnosť o pomoc pri mapovaní tohto druhu. Uvítame najmä živé jedince. Získané jedince je dobré vložiť do vrecúška z látky, výborne poslúžia aj staré silonové pančuchy. Nutné je priložiť lokalitný lístok (vložený do malého igelitového vrecúška, aby ho slimáky nezožrali), na na ktorom je uvedená najbližšia obec, ideálne je pripísať geografické súradnice, ďalej dátum zberu a meno zberateľa, prípadne ďalšie detaily o lokalite (typ biotopu, stanovišťa). Slimáky dáme do chladu (chladničky, pivnice a pod.), ak je to možné, skôr do sucha, aby neboli aktívne. Nutný je prístup vzduchu. Slimáky takto vydržia bez špeciálnej starostlivosti aj niekoľko týždňov.

Podozrivo sfarbené slimáky posielajte na nasledujúcu adresu:

Tomáš Čejka
Botanický ústav SAV

Dúbravská cesta 9
845 23 Bratislava

t.cejka@gmail.com

Samozrejme, na základe dohody, si radi vyzdvihneme materiál hocikde v Bratislave (kontaktný e-mail: t.cejka@gmail.com, ev. juraj.cacany@gmail.com).

References

Korábek, O., Juřičková, L. and Petrusek, A., 2015. Splitting the Roman snail Helix pomatia Linnaeus, 1758 (Stylommatophora: Helicidae) into two: redescription of the forgotten Helix thessalica Boettger, 1886. Journal of Molluscan Studies, p.eyv048.

Korábek, O., Petrusek, A., Neubert, E. and Juřičková, L., 2015. Molecular phylogeny of the genus Helix (Pulmonata: Helicidae). Zoologica Scripta, 44(3), pp.263-280.

Korábek, O. 2016. Hlemýžď pruhovaný, nový druh pro evropskou i českou faunu. Živa 1: 31. Dostupné online.