A new to science valvatiform hydrobiid, Myrtoessa hyas Radea, gen. n. & sp. n., from southern Greece, is described and illustrated. The new genus is a tiny gastropod thriving in a stream and is differentiated from the other known European and circum-Mediterranean valvatiform hydrobiid genera by a unique combination of the male and female genitalia features i.e. penis long, flat, blunt, with wide wrinkled proximal part and narrow distal part with a sub-terminal eversible papilla on its left side, bursa copulatrix well-developed, pyriform, fully protruding from the posterior end of the albumen gland and two seminal receptacles respectively. The new monotypic and locally endemic genus is narrowly distributed and its single known population nearby a coastal bustling village is vulnerable to anthropogenic stressors.

Endemicity, freshwater diversity, hydrobiids, taxonomy

The freshwater fauna around the Mediterranean Basin comprises a plethora of valvatiform hydrobiids (Bodon et al. 2001). Many of them still have unclear taxonomic status because they were established on the basis of shell characters, which are often convergent, and/or those anatomical characters which are frequently non-diagnostic as for instance, stomach (Arconada and Ramos 2006). However, a more detailed anatomical description of some already known valvatiform taxa initially established from shell characters elucidated their taxonomic status (e.g. Bodon et al. 2001, Arconada and Ramos 2002, 2006).

Moreover, during last ten years, several new valvatiform taxa have been described based on shell and diagnostic anatomical characters and, in several cases, their molecular affinities have been investigated (e.g. Bodon et al. 2001, Arconada and Ramos 2006, Arconada and Ramos 2007, Arconada et al. 2007, Radea 2011, Rolan and Pardo 2011, Falniowski and Szarowska 2011a,b, Callot-Girardi and Boeters 2012, Radea et al. 2013).

In Greece, eight valvatiform-planispiral hydrobiid genera, namely Daphniola Radoman, 1973, Fissuria Boeters, 1981, Graecoarganiella Falniowski & Szarowska, 2011a, Hauffenia Pollonera, 1898, Isimerope Radea & Parmakelis, 2013, Islamia Radoman, 1973, Prespolitorea Radoman, 1983 and Pseudoislamia Radoman, 1979, have been recorded so far (Schütt 1980, Radoman 1983, Reischütz and Reischütz 2004, Falniowski and Szarowska 2011a, Radea et al. 2013). Three of them, i.e. Pseudoislamia, Graecoarganiella and Isimerope, are Greek endemics with a rather limited distribution in a few localities of Etoloakarnania, Phokida (central Greece), Argolida and Arkadia (Peloponnisos, southern Greek mainland).

Herein, a new genus and a new species of a minute valvatiform hydrobiid gastropod collected from Mount Parnon, Arkadia are described, and an identification key provided for the valvatiform hydrobiid genera of Greece based on the character states of male and female genitalia.

Snails in question thrived in a stream at Poulithra village, Parnon Mt., Arkadia (Fig. 1); GPS coordinates were taken using a hand-held unit (Magellan Triton 2000). Specimens were collected by hand from stones, gravel, mosses, and dead leaves. Immediately after collection, the specimens were placed into vials filled with water from the collection site and were transported alive to the lab. A digital picture using a camera (Canon EOS 1000D) attached on a stereomicroscope (Stemi 2000-C, Zeiss, Germany), was taken from each sample prior to the addition of any tissue preservation substances.

Figure 1. 

Map showing the distribution of the locally endemic Truncatelloidea in Peloponnisos, southern Greek mainland. Abbreviations: B.a. Bythinella atypicos, B.b. Bythinella beckmanni, D.h. Daphniola hadei, H.e. Hauffenia edlingeri, I.a. Iglica alpeus, I.s. Isimerope semele, I.w. Iglica wolfischeri, M.h. Myrtoessa hyas gen. n., sp. n., P.e. Pseudamnicola exilis, R.f. Radomaniola feheri, R.s. R. seminula, R.t. R. tritonum.

General and diagnostic shell characters were studied and four shell measurements (shell height and width, aperture height and width) were taken from 14 specimens using the micrometer of the Stemi 2000-C stereomicroscope. Four ratios were generated from the raw data (Sh/Sw, Ah/Aw, Sh/Ah and Sw/Aw).

Ten specimens were dissected and studied anatomically under the stereomicroscope using very fine pins and pointed watchmaker’s forceps. Prior to dissection, the shell of each specimen was removed by soaking in Pereny solution. The soft body features were documented using the digital camera as described above.

To remove tissue remaining and debris, the shell, the radula and the operculum were immersed in KOH solution (5g/l) at room temperature, rinsed in distilled water and air-dried before being mounted on stubs. The protoconch, the operculum and the radula were studied using scanning electron microscopy (SEM, Jeol JSM–35 operating at 25 kV) after being dried and spray-coated in gold–palladium.

The authority of the family Hydrobiidae was based on Bouchet and Rocroi (2005). In the description of the morphological characters and their states, the terminology of Hershler and Ponder (1998) was adopted.

A restricted number of specimens (27 specimens in total) was collected from the sampling locality because the population abundance seemed to be low (no specimen was found during the initial 5 min sampling effort). The collected material was deposited in the Zoological Museum (ZMUA) of the National & Kapodistrian University of Athens (UOA) and in the personal collection of C. Radea deposited in the Department of Ecology & Systematics, UOA.

Twelve locally endemic truncatelloidean species (see Reischütz and Reischütz 2004, 2008, Falniowski and Szarowska 2011b, Falniowski et al. 2012, Georgiev 2013, Radea et al. 2013a) have been described from Peloponnese so far (Fig. 1). The high number of endemic truncatelloideans was being expected since the complex topography and the intense geological history of this mainly mountainous area facilitate and promote the diversity and endemicity of invertebrates (Sfenthourakis and Legakis 2001, Legakis and Maragou 2009).

Myrtoessa hyas gen. n. & sp. n. differs from all the known valvatiform hydrobiids in having a unique combination of shell and anatomical characters that according to the standard hydrobiid taxonomy, does not allow its inclusion in any other known genus of the Hydrobiidae family. Consequently, a new monotypic genus is necessary to accommodate it.

The combination of the features of male and female genitalia followed by Bodon et al. (2001) for distinguishing the known genera of valvatiform Hydrobiidae shows that the new genus is clearly differentiated from the other European and circum-Mediterranean valvatiform genera (Table 2) having bursa copulatrix and two seminal receptacles by the penial characters. These genera are further differentiated from Myrtoessa gen. n. in having, among others, an operculum with peg (Bracenica Radoman, 1973, Gocea Hadzǐšiče 1956), no eyes (Fissuria, Pezzolia Bodon & Giusti, 1986, Sardohoratia Manganelli, Bodon, Cianfanelli, Talenti & Giusti, 1998), different shape of rectum (Corbellaria Callot-Girardi & Boeters, 2012, Fissuria, Graecoarganiella, Horatia Bourguignat, 1887, Iberhoratia Arconada & Ramos, 2007, Pezzolia Bodon & Giusti 1986, Sardohoratia).

The opening of penial duct through a sub-terminal papilla is a novel character recorded for the first time in the valvatiform hydrobiids of Europe and Mediterranean Basin since, up to now, only a terminal papilla has been recorded (Table 2). The other valvatiform genera having a penial papilla, i.e. Fissuria, Graecoarganiella and Isimerope, are distinguished from Myrtoessa gen. n. by the position of the papilla, the different overall shape of the penis, the female genitalia (Isimerope) and other characters detailed in Table 2.

The new genus inhabits a stream with cold and clear fast running water. The rest known valvatiform genera of Greece thrive in various freshwater systems: Islamia and Pseudoslamia in lakes, springs and streams, Isimerope in springs and rivers, Fissuria in subterranean waters, Daphniola, Hauffenia and Graecoarganiella in springs and Prespolittorea in lakes (Radoman 1983, Reischütz 1988, 2004, Bodon et al. 2001, Falniowski and Szarowska 2011a, Radea et al. 2013a,b).

The single population of Myrtoessa hyas gen. n. & sp. n. nearby a coastal touristic village is vulnerable to anthropogenic stressors, in particular during the summer period, due to the numerous tourists, visitors, and hikers as well as to the increased demands for water supply and irrigation.

In last three years, one new locally endemic monotypic truncatelloidean genus, i.e. Isimerope (Radea et al. 2013), and seven new locally endemic species i.e. Radomaniola feheri Georgiev, 2013 (Georgiev 2013), Daphniola magdalenae Falniowski, 2015, Iglica hellenica Falniowski, 2015 (Falniowski and Sarbu 2015), Pseudamnicola ianthe Radea & Parmakelis, 2016, P. ilione Radea & Parmakelis, 2016 (Radea et al. 2016), P. magdalenae Falniowski, 2016 (Falniowski 2016a), and Bythinella walensae Falniowski, 2016 (Falniowski 2016b) were described from Greece. The introduction of one more new locally endemic genus provides clues about the richness and the high endemicity of Greek freshwater bodies, which support some of the most biodiverse and heavily threatened ecosystems of the Mediterranean Basin Biodiversity Hotspot (Szarowska and Falniowski 2004, Darwall et al. 2014).

We wish to thank A. Economou-Amilli for the scanning electron micrographs, Th. Constantinidis, E. Kalpoutzakis for collecting additional material, G. Tryfonopulos and the staff of Management Body of Mount Parnon and Moustos wetlands for their help in the field. The fieldwork was done under a collection permit (ref. no. 111704/1686) issued by the Greek Ministry of Environment, Energy and Climate Change. The manuscript was improved by the useful comments and suggestions of Subject Editor M. Haase and two anonymous reviewers.