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Research Article
A new species of Kerkia Radoman, 1978 (Caenogastropoda, Hydrobiidae) from Bosnia and Herzegovina
expand article infoSebastian Hofman, Aleksandra Rysiewska, Artur Osikowski§, Andrzej Falniowski
‡ Jagiellonian University, Kraków, Poland
§ University of Agriculture, Kraków, Poland
Open Access

Abstract

A new species of Kerkia, K. briani Rysiewska & Osikowski, sp. nov. is described from the spring Polički Studenac Vrelo (Crkvina), adjacent to the Trebišnjica River (Bosnia and Herzegovina) collected with Bou-Rouch technique, pumped from an interstitial habitat 50 cm below the bottom of the spring. The shell, female reproductive organs, and the penis are described and illustrated. Mitochondrial cytochrome oxidase subunit I (COI) and nuclear histone H3 partial sequences confirm the distinctness of the new species, and molecularly based phylogenetic relationships of Kerkia are briefly presented.

Keywords

Balkans, cytochrome oxidase, Gastropoda, histone, interstitial, molecular taxonomy, morphology, stygobiont

Introduction

Mud snails Hydrobiidae are very small or minute snails, whose shells are often approximately 1 mm high. They inhabit surface and subterranean freshwater habitats, although some can also be found in brackish and even marine environments. The family comprises more than 400 extant genera (Kabat and Hershler 1993), many of which are stygobionts. The Balkans, especially their western region, harbours the world’s most diverse stygobiont malacofauna (e.g., Culver and Sket 2000; Culver 2012). The minute dimensions of those snails, coupled with low population densities (e.g., Culver and Pipan 2009, 2014), result in very poor knowledge of their biology, speciation, and taxonomy. A few specimens are sometimes flooded out of the substrate to the surface. Otherwise, extensive pumping of the interstitial habitats, applying the Bou and Rouch technique sometimes result in more numerous living specimens.

Radoman (1978) established the genus Kerkia Radoman, 1978, with the type species Hauffenia kusceri Bole, 1961, known only from the cave Krška jama in Slovenia. He described morphology and anatomy of those minute snails, clinging to the rocks in the underground section of the sinking river Krka (Radoman 1973, 1978, 1983). Later, another species of the genus, K. brezicensis Bodon & Cianfanelli, 1996, was described from a karstic spring at the entry to Dvorce village, southeast of Brežice in Slovenia. Hauffenia jadertina Kuščer, 1933 from the source of the river Jadro near Split in Croatia, as well as H. jadertina sinjana Kuščer, 1933 from a spring Zužino Vrelo in the Cetina valley also in Croatia, based on their anatomy, were synonymised and transferred to the genus Kerkia by Beran et al. (2014), who also described a new species Kerkia kareli Beran, Bodon & Cianfanelli, 2014, from an old well near Povljana on island Pag in Croatia. They provided descriptions and illustrations of the shells, protoconchs, radulae, and soft part morphology and anatomy as well for all the three Croatian taxa. Rysiewska et al. (2017) demonstrated molecular distinctness of those species of Kerkia.

In September of 2019, in the spring Polički Studenac Vrelo (Crkvina), adjacent to the Trebišnjica River, we found Emmericia expansilabris Bourguignat, 1880, Sadleriana sp., Anagastina vidrovani (Radoman, 1973), and Ancylus recurvus Martens, 1873. Pumping of the interstitial fauna from sediments below the spring resulted in the collection of a few most probably stygophilic Radomaniola, but also the typically stygobiont Montenegrospeum Pešić & Glöer, 2013 and Kerkia. The representatives of the latter genus did not belong to any species known so far, and in the present paper we describe this new species and discuss its relationships.

Materials and methods

The snails were collected at the spring Polički Studenac Vrelo (Crkvina), adjacent to the Trebišnjica River (42°42'46.4"N, 18°21'54.5"E), near Trebinje, Bosnia and Herzegovina (Fig. 1). The spring, situated at the right bank of the river (Fig. 2A, B) was in the form of a small shallow pool surrounded by a wall made of stones, with a gravel bottom (Fig. 2C). The Bou–Rouch method (Bou and Rouch 1967) was used to sample interstitial fauna below the spring bottom, at the depth of ca. 50 cm. The tube was inserted in the substrate five times, and 20 litres were pumped each time. Samples were sieved through 500 μm sieve and fixed in 80% analytically pure ethanol, replaced two times, and later sorted. Next, the snails were put in fresh 80% analytically pure ethanol and kept in -20 °C temperature in a refrigerator.

Figure 1. 

Localities of Kerkia used for phylogeny.

Figure 2. 

Type locality of Kerkia briani sp. nov.: A, B River Trebišnjica with the spring Polički Studenac Vrelo at its right bank C the spring from where interstitial snails were pumped.

The shells were photographed with a Canon EOS 50D digital camera, under a Nikon SMZ18 microscope. The dissections were done under a Nikon SMZ18 microscope with dark field, equipped with Nikon DS-5 digital camera, whose captured images were used to draw anatomical structures with a graphic tablet. Measurements of the shell (Fig. 3) were taken using ImageJ image analysis software (Rueden et al. 2017).

Figure 3. 

Measurements of the shell.

Snails for molecular analysis were fixed in 80% ethanol, changed twice, and later stored in 80% ethanol. DNA was extracted from whole specimens; tissues were hydrated in TE buffer (3 × 10 min), total genomic DNA was extracted with the SHERLOCK extraction kit (A&A Biotechnology), and the final product was dissolved in 20 μl of tris-EDTA (TE) buffer. The extracted DNA was stored at -80 °C at the Department of Malacology, Institute of Zoology and Biomedical Research, Jagiellonian University in Kraków (Poland).

DNA coding for mitochondrial cytochrome oxidase subunit I (COI) and nuclear histone 3 (H3) were sequenced. Details of PCR conditions, primers used, and sequencing are given in Szarowska et al. (2016b). Sequences were initially aligned in the MUSCLE (Edgar 2004) programme in MEGA 6 (Tamura et al. 2013) and then checked in BIOEDIT 7.1.3.0 (Hall 1999). Uncorrected p-distances were calculated in MEGA 6. The estimation of the proportion of invariant sites and the saturation test (Xia 2000; Xia et al. 2003) were performed using DAMBE (Xia 2013). In the phylogenetic analysis additional sequences from GenBank were used as reference (Table 1). The data were analysed using approaches based on Bayesian Inference (BI) and Maximum Likelihood (ML). We applied the GTR model whose parameters were estimated by RaxML (Stamatakis 2014). The Bayesian analyses were run using MrBayes v. 3.2.3 (Ronquist et al. 2012) with defaults of most priors. Two simultaneous analyses were performed, each with 10,000,000 generations, with one cold chain and three heated chains, starting from random trees and sampling the trees every 1,000 generations. The first 25% of the trees were discarded as burn-in. The analyses were summarised as a 50% majority-rule tree. The Maximum Likelihood analysis was conducted in RAxML v. 8.2.12 (Stamatakis 2014) using the ‘RAxML-HPC v.8 on XSEDE (8.2.12)’ tool via the CIPRES Science Gateway (Miller et al. 2010). Two species delimitation methods were performed: Poisson Tree Processes (PTP) (Zhang et al. 2013) and Automatic Barcode Gap Discovery (ABGD). The PTP approach was run using the web server https://species.h-its.org/ptp/, with 100 000 MCMC generations, 100 thinning and 0.1 burn-in. We used RAxML output phylogenetic tree. The ABGD approach using the web server (http://www.abi.snv.jussieu.fr/public/abgd/abgdweb.html) and the default parameters.

Table 1.

Taxa used for phylogenetic analyses with their GenBank accession numbers and references.

Species COI/H3 GB numbers References
Agrafia wiktori Szarowska & Falniowski, 2011 JF906762/MG543158 Szarowska and Falniowski 2011/Grego et al. 2017)
Alzoniella finalina Giusti & Bodon, 1984 AF367650 Wilke et al. 2001
Amnicola limosus (Say, 1817) AF213348 Wilke et al. 2000b
Anagastina zetavalis (Radoman, 1973) EF070616 Szarowska 2006
Avenionia brevis berenguieri (Draparnaud, 1805) AF367638 Wilke et al. 2001
Belgrandia thermalis (Linnaeus, 1767) AF367648 Wilke et al. 2001
Belgrandiella kuesteri (Boeters, 1970) MG551325/MG551366 Osikowski et al. 2018
Bithynia tentaculata (Linnaeus, 1758) AF367643 Wilke et al. 2001
Bythinella cretensis Schütt, 1980 KT353689 Szarowska et al. 2016a
Bythinella hansboetersi Glöer & Pešić, 2006 KT381101 Osikowski et al. 2015
Bythiospeum acicula (Hartmann, 1821) KU341350/ MK609536 Richling et al. 2016/Falniowski et al. 2019
Bythiospeum alzense Boeters, 2001 KU341355 Richling et al. 2016
Ecrobia maritima (Milaschewitsch, 1916) KX355835/MG551322 Osikowski et al. 2016/Grego et al. 2017
Daphniola louisi Falniowski & Szarowska, 2000 KM887915 Szarowska et al. 2014c
Dalmatinella fluviatilis Radoman, 1973 KC344541 Falniowski and Szarowska 2013
Emmericia expansilabris Bourguignat, 1880 KC810060 Szarowska and Falniowski 2013a
Erhaia jianouensis (Y.-Y. Liu & W.-Z. Zhang, 1979) AF367652 Wilke et al. 2001
Fissuria boui Boeters, 1981 AF367654 Wilke et al. 2001
Graecoarganiella parnassiana Falniowski & Szarowska, 2011 JN202352 Falniowski and Szarowska 2011
Graziana alpestris (Frauenfeld, 1863) AF367641 Wilke et al. 2001
Grossuana angeltsekovi Glöer & Georgiev, 2009 KU201090 Falniowski et al. 2016
Hauffenia michleri (Kuščer, 1932) KT236156/KY087878 Falniowski and Szarowska 2015/ Rysiewska et al. 2017
Heleobia maltzani (Westerlund, 1886) KM213723/ MK609534 Szarowska et al. 2014b/ Falniowski et al. 2019
Horatia klecakiana Bourguignat 1887 KJ159128 Szarowska and Falniowski 2014
Hydrobia acuta (Draparnaud, 1805) AF278808 Wilke et al. 2000a
Iglica cf. gracilis (Clessin, 1882) MH720985/ MH721003 Hofman et al. 2018
Iglica hellenica Falniowski & Sarbu, 2015 KT825581/MH721007 Falniowski and Sarbu 2015/Hofman et al. 2018
Islamia zermanica (Radoman, 1973) KU662362/MG551320 Beran et al. 2016/Grego et al. 2017
Kerkia jadertina (Kuščer, 1933) KY087868/KY087885 Rysiewska et al. 2017
Kerkia jadertina sinjana (Kuščer, 1933) KY087873-74/ KY087890-91 Rysiewska et al. 2017
Kerkia kareli Beran, Bodon & Cianfanelli, 2014 KY087875-77/ KY087892-94 Rysiewska et al. 2017
Kerkia kusceri (Bole, 1961) KY087867/KY087884 Rysiewska et al. 2017
Kerkia sp. Ljubač KY087872/KY087889 Rysiewska et al. 2017
Littorina littorea (Linnaeus, 1758) KF644330/KP113574 Layton et al. 2014/Neretina 2014, unpublished
Littorina plena Gould, 1849 KF643257 Layton et al. 2014
Lithoglyphus prasinus (Küster, 1852) JX073651 Falniowski and Szarowska 2012
Marstoniopsis insubrica (Küster, 1853) AF322408 Falniowski and Wilke 2001
Moitessieria cf. puteana Coutagne, 1883 AF367635/MH721012 Wilke et al. 2001/ Hofman et al. 2018
Montenegrospeum bogici (Pešić & Glöer, 2012) KM875510/MG880218 Falniowski et al. 2014/Grego et al. 2018
Paladilhiopsis grobbeni Kuščer, 1928 MH720991/MH721014 Hofman et al. 2018
Peringia ulvae (Pennant, 1777) AF118302 Wilke and Davis 2000
Pomatiopsis lapidaria (Say, 1817) AF367636 Wilke et al. 2001
Pontobelgrandiella sp. Radoman, 1978 KU497024/MG551321 Rysiewska et al. 2016/Grego et al. 2017
Pseudamnicola chia (E. von Martens, 1889) KT710656 Szarowska et al. 2016b
Pseudorientalia Radoman, 1973 – Lesvos KJ920490 Szarowska et al. 2014a
Radomaniola curta (Küster, 1853) KC011814 Falniowski et al. 2012
Sadleriana fluminensis (Küster, 1853) KF193067 Szarowska and Falniowski 2013b
Sadleriana robici (Clessin, 1890) KF193071 Szarowska and Falniowski 2013b
Salenthydrobia ferrerii Wilke, 2003 AF449213 Wilke 2003
Sarajana apfelbecki (Brancsik, 1888) MN031432 Hofman et al. 2019
Tanousia zrmanjae (Brusina, 1866) KU041812 Beran et al. 2015
Tricula sp. Benson, 1843 AF253071 Davis et al. 1998

Results

Systematic part

Family Hydrobiidae Stimpson, 1865

Subfamily Sadlerianinae Szarowska, 2006

Genus Kerkia Radoman, 1978

Kerkia briani Rysiewska & Osikowski, sp. nov.

Figures 4, 5, 6A, B, 7

Holotype

Ethanol-fixed specimen (Fig. 4), spring Polički Studenac Vrelo (Crkvina), adjacent to the Trebišnjica River (42°42'46.4"N, 18°21'54.5"E), close to Trebinje (Bosnia and Herzegovina interstitially in the gravel 50 cm below the bottom of the spring. It is deposited in the Museum of Natural History of the University of Wroclaw, Poland, signature: MNHW-1350.

Figure 4. 

Holotype of Kerkia briani. Scale bar: 0.5 mm.

Paratypes

Twelve paratypes, ethanol-fixed, in the collection of the Department of Malacology of Jagiellonian University.

Diagnosis

Shell minute, nearly planispiral, distinguished from K. kusceri by its lower aperture of the shell and smaller non-glandular outgrowth on the left side of the penis, and from K. jadertina and K. kareli by its higher aperture of the shell and bigger the non-glandular outgrowth on the left side of the penis.

Description

Shell (Fig. 4) up to 0.77 mm high and 1.39 mm broad, nearly planispiral, whitish, translucent, thin-walled, consisted of approximately five whorls, growing rapidly and separated by moderately deep suture. Spire low and flat, body whorl large. Aperture prosocline, nearly circular in shape, peristome complete and thin, somewhat swollen, in contact with the wall of the body whorl; umbilicus wide, with the earlier whorls visible inside. Shell surface smooth, growth lines hardly visible.

Measurements of holotype, sequenced, and illustrated shells: see Table 2. Shell variability slight (Fig. 5).

Table 2.

Shell measurements (in mm) of Kerkia briani. For explanation of the symbols A–H, see Fig. 3.

A B C D E F G H
holotype 0.77 1.39 0.87 0.62 0.60 1.09 0.41 0.97
2D44 0.72 1.12 0.73 0.54 0.55 0.93 0.37 0.75
2F59 0.73 1.26 0.82 0.54 0.55 0.95 0.41 0.80
2F62 0.72 1.35 0.86 0.57 0.57 1.03 0.36 0.73
2F70 0.67 1.12 0.72 0.52 0.48 0.97 0.40 0.72
2F71 0.75 1.37 0.85 0.46 0.60 1.02 0.41 0.84
M 0.73 1.27 0.81 0.54 0.56 1.00 0.39 0.80
SD 0.034 0.123 0.067 0.053 0.044 0.059 0.023 0.094
Min 0.67 1.12 0.72 0.46 0.48 0.93 0.36 0.72
Max 0.77 1.39 0.87 0.62 0.60 1.09 0.41 0.97
Figure 5. 

Shell variability of Kerkia briani, labels the same as in the molecular trees. Scale bar: 0.5 mm.

Soft parts morphology and anatomy. Body white, without pigment, with no eyes. The ctenidium with twelve short lamellae, osphradium short and broad. Rectum forming characteristic broad loop (Fig. 6A). The female reproductive organs (Fig. 6A, B) with a long, moderately broad loop of renal oviduct and relatively big spherical bursa copulatrix (Fig. 6A) with a long bent duct (Fig. 6B), and one distal receptaculum seminis, long and worm-shaped. The penis (Fig. 7) elongated triangular, with a rather sharp tip and small non-glandular outgrowth on its left side, the vas deferens inside running in zigzags.

Figure 6. 

Renal and pallial section of the female reproductive organs of Kerkia briani: A the loop of oviduct in its normal position and the loop of the rectum B the loop of oviduct moved to show the receptaculum seminis and duct of bursa. Abbreviations: bc – bursa copulatrix, cbc – duct of bursa, ga – albuminoid gland, gn – nidamental gland, gp – gonoporus, ov – oviduct, ovl – loop of renal oviduct, rec – rectum, rs – receptaculum seminis. Scale bars: 1 mm.

Figure 7. 

Penis of Kerkia briani. Abbreviation: vd – vas deferens.Scale bar: 1 mm.

Derivatio nominis

The specific epithet briani refers to our friend Brian Lewarne, Honorary Science Officer of The Devon Karst Research Society, and the Director for “Proteus Project in the Trebišnjica River Basin”, deeply devoted to the protection of Proteus as well as the study and protection of the subterranean habitats in Bosnia and Herzegovina.

Distribution and habitat

Known from the type locality only.

Molecular distinctness and relationships of Kerkia briani

We obtained six new sequences of COI (479 bp, GenBank Accession Numbers MT780191MT780196), and six new sequences of H3 (309 bp, GenBank Accession Numbers MT786730MT786735). The tests by Xia et al. (2003) for COI and H3 revealed no saturation. Phylograms were constructed for COI, H3 and for combined COI-H3 dataset. In all analyses, the topologies of the resulting phylograms were identical in both the ML and BI. The ABGD and PTP approaches gave the same results (Fig. 8).

Figure 8. 

Maximum Likelihood tree inferred from mitochondrial COI. Bootstrap supports above 60% with corresponding Bayesian probabilities are given.

The sequences of the Kerkia briani formed distinct clade on COI, H3 as well as combined phylograms (Fig. 8). At the same time all Kerkia sequences formed distinct linage with five different species. The p-distance of Kerkia briani with other Kerkia species varied from 0.123 to 0.146 for COI and from 0.007 to 0.023 for H3 (Table 2). The sister clade of Kerkia (bootstrap support 98%) were Islamia Radoman, 1973, Pontobelgrandiella Radoman, 1978, Belgrandiella Wagner, 1927, Montenegrospeum Pešić & Glöer, 2013, Hauffenia Pollonera, 1898, and Agrafia Szarowska & Falniowski, 2011 (Fig. 8, the tree for concatenated COI and H3 sequences).

Table 3.

p-distances between Kerkia mOTUs for the COI (below diagonal) and H3 genes.

mOTU – A mOTU – B mOTU – C mOTU – D mOTU – E
mOTU – A 0.010 0.007 0.010 0.023
mOTU – B 0.135 0.017 0.020 0.033
mOTU – C 0.126 0.124 0.010 0.023
mOTU – D 0.146 0.138 0.124 0.013
mOTU – E 0.123 0.110 0.095 0.093

Discussion

Following the terminology of Hershler and Ponder (1998), the habitus of the shell of Kerkia is depressed valvatiform (trochiform) or just planispiral. However, the latter term should not be used, since there is no planispiral shell in any recent gastropod (e.g., Falniowski 1993). The ctenidium, osphradium, and loop of oviduct are as in the other species of Kerkia (Bodon et al. 2001; Beran et al. 2014). The female reproductive organs are also typical of Kerkia (Radoman 1978, 1983; Bodon et al. 2001; Beran et al. 2014). The single receptaculum seminis is situated distally, in the position of rs1 after Radoman (1973, 1983). The penis is similar to that described and drawn by Radoman (1978, 1983), Bodon et al. (2001), and Beran et al. (2014), but the outgrowth of its left side in K. briani is smaller than in K. kusceri, but larger than that in K. jadertina and K. kareli (in the latter the outgrowth is nearly vestigial).

Falniowski (1987) demonstrated high variability of the shell, but also of the morphology and anatomy of the soft parts in the Truncatelloidea. In the latter, miniaturisation is one more a source of slight morphological diversity, decreasing the number of possible taxonomically useful characters (Falniowski 2018); in this regard, Szarowska and Falniowski (2008) stressed the narrow limits of morphology-based taxonomy within the Truncatelloidea. On the other hand, Szarowska (2006) demonstrated that such simple structures like the outgrowths on the penis and bursae/receptacula in the female reproductive organs are surprisingly evolutionary stable in position, although not in size and shape, whose variability – physiologically, ontogenetically, and artifactually (as a result of fixation of the snails) based – is striking. Moreover, problems can increase with taxa living in habitats of limited accessibility (such as caves and/or interstitial habitats) for which molecular studies often reveal numerous species but only a few or single living specimens of each species could be found. Thus, the anatomy is basic in distinction of the families and even genera, but the stable and reliable differences between congeneric species are hardly observable. However, the molecular distinctness of Kerkia briani is clear.

Finally, it has to be pointed out that K. briani inhabits the southernmost locality of Kerkia, expanding the range of the genus ca. 190 km ESE.

Acknowledgments

The study was supported by a grant from the National Science Centre 2017/25/B/NZ8/01372 to AF.

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