Archives of Zoological Studies Category: Agriculture Type: Review Article
Species Distinction and Speciation in Hydrobioid Gastropods (Mollusca: Caenogastropoda: Truncatelloidea)
- Andrzej Falniowski1*
- 1 Department Of Malacology, Institute Of Zoology And Biomedical Research, Jagiellonian University, Krakow, Poland
*Corresponding Author:Andrzej Falniowski
Department Of Malacology, Institute Of Zoology And Biomedical Research, Jagiellonian University, Krakow, Poland
Tel:+48 609 111 950,
Received Date: Nov 29, 2017 Accepted Date: Jan 29, 2018 Published Date: Feb 12, 2018
Hydrobioids, known earlier as the family Hydrobiidae, represent a set of truncatelloidean families whose members are minute, world-wide distributed snails inhabiting mostly springs and interstitial waters. More than 1,000 nominal species bear simple plesiomorphic shells, whose variability is high and overlapping between the taxa, and the soft part morphology and anatomy of the group is simplified because of miniaturization, and unified, as a result of necessary adaptations to the life in freshwater habitats (osmoregulation, internal fertilization and eggs rich in yolk and within the capsules). The adaptations arose parallel, thus represent homoplasies. All the above facts make it necessary to use molecular markers in species discrimination, although this should be done carefully, considering genetic distances calibrated at low taxonomic level. There is common believe in crucial place of isolation as a factor shaping speciation in long-lasting completely isolated habitats. However, neither geomorphological facts (springs are rather ephemeral habitats, there is a net of interstitial habitats which may be used as the ways of expansion), nor the actual genetic structure of (Meta) populations of those stygobiont gastropods (not necessarily low intrapopulation polymorphism, not low levels of gene flow) confirm such opinion.
Shells of some of the European representatives of Truncatelloidea: A - Ecrobia, B - Pyrgula, C-D - Dianella, E - Adrioinsulana, F - Pseudamnicola, G - Sadleriana, H - Radomaniola, I - Anagastina, J - Grossuana, K - Hauffenia, L - Graecorientalia, M - Trichonia, N - Daphniola, O -Boleana, P - Graziana, Q - Pontobelgrandiella, R - Paladilhiopsis, S - Litthabitella, T - Pseudobithynia, U - Bythinella, W - Lithoglyphus, X - Emmericia, Y - Marstoniopsis, Z – Heleobia.
MORPHOLOGICAL CHARACTERS IN SPECIES DISTINCTION
Anatomical characters, especially of the reproductive system, became a standard in species-level taxonomy in hydrobioids. The anatomy of the female reproductive system as well as the morphology of the penis was considered in species descriptions and diagnoses [9-23]. On the other hand, there are opinions that between the closely related representatives of the same genus, differences in anatomy are not necessarily present, and, in many cases, would not be expected . The 'lock-and-key' mechanism, known mostly in arthropods, is hardly expected in molluscs, whose copulatory organs lack any sclerotized structures, and are more variable than it is usually noted [1,25-28].
In hydrobioids the anatomy does not offer too many characters useful for taxonomy. It is simplified as a result of miniaturisation and made similar because of inevitable adaptations to osmoregulation, internal fertilization, and embryonic development inside a capsule, all necessary in a freshwater habitat, but not plesiomorphic for the Gastropoda. Thus, anatomical similarities are the result of parallelism, or even convergence, at least in many cases, and need not necessarily reflect the common ancestry. In general, homoplasies are common in the Mollusca [29-31].
SPECIES CONCEPTS APPLIED IN HYDROBIOID; INTRODUCTION OF MOLECULAR DATA
Unfortunately, we often know too little about the ecology and biology of the hydrobioid taxa to apply this concept. Often a few specimens or only empty shells - sometimes even broken, incomplete - can be found, thus the taxonomy is based mostly on the shell morphology and geographic distribution. This, coupled with a popular idea that isolation is the first factor shaping divergence and speciation of the spring/cave fauna, resulted in dozens of nominal species in many genera, the species known only as shells at a given locality. Thus, with well-fixed material available, it became necessary to apply molecular data . Especially the relative range of genotypic differentiation, measured as simple p-distance (or, often, K2P distance which is not justified, but the values are sonly somewhat higher than the ones of p-distance), most often calculated for mitochondrial cytochrome oxidase subunit I (COI, commonly used in phylogenetic studies: Davis et al.,), are used [35,36]. It must be stressed, however, that the values of the distances are applicable only within a group of rather closely related species, since there is no general rule, in some genera the interspecies distances are higher, in some other they are smaller [4,37-45]. For example, Bichain et al., reported that the species threshold value of K2P distance in the west European Bythinella was 0.015 . Several numerical techniques for species distinction applying the genetic distances were introduced [46,47]. Applying mitochondrial DNA one should be careful since there are cases of introgression, although not often .
MORPHOSTATIC MODE OF EVOLUTION
WAYS OF SPECIATION
Undoubtedly the levels of endemism are overestimated, and type specimens stored as empty shells are hardly helpful in solving problems with identification and species boundaries in the hydrobioid snails. In stygobiont hydrobioids living snails can be collected as single specimens, only exceptionally a few specimens can be collected at a place, thus the molecular data, useful in phylogeny as well as in the studies on genetic structure of population, only recently begun to accumulate . It is commonly believed that the springs inhabited by those obligatorily aquatic animals are stable and long lasting habitats. Certainly this cannot be truth: springs are rather ephemeral habitats. Another widely acknowledged idea is that the gene flow among them, if at all present, is very low. In the rich literature covering the phylogeny and population genetic structure and gene flow of the spring fauna, the gastropods are well represented [49,57,58,62-71]. Most of the studies point to low levels of gene flow and high levels of endemism in spring snails, but on the other hand, some of the species the studies deal with are rather widespread, with much gene flow among their populations [57,58,62,63,67,71].
For long the one-species-at-one-locality view was widely accepted concerning spring-dwelling hydrobioids, like Bythinella [1,49]. This argument assumed that: (i) closely phylogenetically related snails have most probably the same or almost the same ecological niche; (ii) there is little or no spatial differentiation inside small and simple habitats like springs. Neither argument need be true. Firstly, the ecological niches of closely related species do not necessarily overlap. Secondly, even the smallest spring may contain more than one microhabitat. On the other hand, one can assume that two species whose ecological niches overlap will coexist if their densities are limited not by their competition, but some other factors (e.g. parasites). Falniowski et al., found an evident case of sympatric occurrence of two Bythinella species in Romania: striking morphological differences coupled with the molecular ones [40,49]. Two molecularly distinct sympatric taxa of Bythinella were found also in Greece and morphologically different - in Slovenia [24,26,72].
ISOLATION VS GENE FLOW
The several cases of presumed long-distance passive transportation (the sea included), reflected by genetic identity/similarity, were reported in several studies [26,74,75]. They confirm that passive dispersal, most probably by birds is an important factor that moulds the geographical distribution of haplotypes [76-79]. There are no observations on the bird transport of spring snails, but the data on snails transported by birds are numerous. Lyell mentioned the possibility of transport by waterfowl to distant islands for a land snail Succinea putris through the attachment of eggs to feathers and Darwin observed ducks emerging from a pond with duckweed adhering to their backs [80,81]. For the hydrobioids, Bondesen & Kaiser mentioned a possibility for Potamopyrgus antipodarum and other prosobranchs of attaching themselves to feathers by trapping them between operculum and shell. Cadée observed living Peringia ulvae emerging from faeces of the shelduck, Tadorna tadorna, indicating that they survived the passage of the digestive tract [82-84]. The numbers of Peringia observed alive in the shelduck’s faeces were considerable: three droppings contained in total 140 living specimens and 960 empty and/or broken Peringia shells .
Animals adapted to cave environments are also thought to be highly geographically isolated because of their limited dispersal ability, resulting from limited physiological tolerances and, especially in the case of snails, physical limitations of their locomotion [85,86]. However, this isolation is not obvious. In fact, there are many subterranean habitats which are not caves, but also harbour eyeless, depigmented animals, especially unconsolidated sediments bordering and underlying streams and rivers. They are parts of the interstitial habitat, neither rare nor discontinuous, making thus possible migration between caves [87-91].
And, last but not least, nearly all the debate concerns the isolation as the only factor shaping speciation in stygobiont snails. This need not to be justified: at first, even in isolation, speciation need not to proceed, in a habitat which is stable but not necessarily favourable for an animal, there would be either no mutation or each mutation would be eliminated by strong selection. Extremely low level of genetic diversity in stygobiont Pontobelgrandiella throughout Bulgaria may be an example. On the other hand, sympatric speciation must be also considered in the debate on the stygobiont species and speciation [92-94].
- Falniowski A (1987) Hydrobioidea of Poland (Prosobranchia: Gastropoda). Folia Malacol 1: 11-122.
- Falniowski A (1990) Anatomical characters and SEM structure of radula and shell in the species-level taxonomy of freshwater prosobranchs (Mollusca: Gastropoda: Prosobranchia): a comparative usefulness study. Folia Malacol 4: 53-
- Wilke T, Falniowski A (2001) The genus Adriohydrobia (Hydrobiidae: Gastropoda): polytypic species or polymorphic populations? J Zool Syst Evol Res 39: 227-234.
- Falniowski A, Beran L (2015) Belgrandiella J. Wagner, 1928 (Caenogastropoda: Truncatelloidea: Hydrobiidae): how many endemics? Folia Malacol 23:187-191.
- Roszkowski W (1914) Contribution à l’etude des Limnées du lac Léman. Rev Suis Zool 22: 453-539.
- Hubendick B (1951) Recent Lymnaeidae, their variation, morphology, taxonomy, nomenclature, and distribution. Almqvist publisher, Sweden. 3: 1- 223.
- Muus BJ (1963) Some Danish Hydrobiidae with the description of a new species Hydrobia neglecta. Proc Malac Soc Lond 35: 131-138.
- Muus BJ (1967) The fauna of Danish estuaries and lagoons: distribution and ecology of dominating species in the shallow reaches of the mesohaline zone. University of California, California, USA. 5: 1-316.
- Giusti F, Pezzoli E (1977) Primo contributo alla revisione del genere Bythinella in Italia. Nat Bresc Ann Mus Civ St Nat Brescia 14: 3-80.
- Giusti F, Pezzoli E (1980) Gasteropodi, 2 (Gastropoda: Prosobranchia; Hydrobioidea, Pyrguloidea). Guide per ilriconoscimentodelle specie animalidelleacque interne, NHBS, UK.
- Jungbluth JH, Boeters HD (1977) ZurArtabgren zungbei Bythinella dunkeriund bavarica (Prosobranchia). Malacologia 16: 143-147.
- Boeters HD (1970) Die Gattung Microna Clessin, 1890 (Prosobranchia, Hydrobiidae). Arch Molluskenk 100: 113-145.
- Boeters HD (1998) Mollusca: Gastropoda: Superfamilie Rissooidea. In: Brauer A, Schwoerbel J, Zwick P (eds.). Süsswasserfauna von Mitteleuropa. Cornell Univeristy, Cornell, USA.
- Bodon M (1988) Note anatomischesu “Belgrandiella” hartwigschuetti Reischütz e revision della sua posizione sistematica (Gastropoda: Prosobranchia: Hydrobiidae). Arch Molluskenk 119: 55-63.
- Haase M (1993) Hauffeniakerschneri (Zimmermann 1930): zweiArtenzweier Gattungen (Caenogastropoda: Hydrobiidae). Arch Molluskenk 121: 91-109.
- Haase M (1993) Belgrandiella ganslmayri, a new hydrobiid species from Upper Austria (Caenogastropoda). Ann Naturh Mus Wien 94/95: 181-186.
- Haase M (1994) Differentiation of selected species of Belgrandiella and the redefined genus Graziana (Gastropoda: Hydrobiidae). Zool J Linn Soc Lond 111: 219-246.
- Haase M (1996) The radiation of spring snails of the genus Belgrandiella in Austria (Mollusca: Caenogastropoda: Hydrobiidae). Hydrobiologia 319: 119-129.
- Bernasconi R (1994) Le genre Moitessieria BGT, 1863 en France. Revision, inventaire et description de corsica n. sp. (Mollusca Gasteropoda Prosobranchia Hydrobiidae). Mém Biospéol 21: 7-20.
- Bernasconi R (2000) Révision du Genre Bythinella (Moquin-Tandon, 1855) (Gastropoda Prosobranchia Hydrobiidae: Amnicolinae Bythinellini) de la France du Centre-Ouest, du Midi et des Pyréné University of California, California, USA. 1: 1-126.
- Haase M, Weigand E, Haseke H (2000) Two new species of the family Hydrobiidae (Mollusca: Caenogastropoda) from Austria. Veliger 43: 179-189.
- Bodon M, Manganelli G, Giusti F (2001) A survey of the European valvatiform hydrobiid genera, with special reference to Hauffenia Pollonera, 1898 (Gastropoda: Hydrobiidae). Malacologia 43: 103-215.
- Glöer P (2002) Süsswassergastropoden Nord- und Mitteleuropas. Bestimmungsschlüssel, Lebensweise, Verbreitung: Part 73 of Die Tierwelt Deutschlands und der angrenzenden Meeresteile nach ihren Merkmalen und nach ihrer Lebensweise (edn2). ConchBooks, Hackenheim, Germany.
- Radoman P (1983) Hydrobioidea a superfamily of Prosobranchia (Gastropoda). Systematics (Vol 1). Srpska akademija nauka i umetnosti, Belgrade, Serbia.
- Masly JP (2012) 170 Years of “Lock-and-Key”: Genital Morphology and Reproductive Isolation. Int J Evol Biol 2012: 247352.
- Falniowski A, Szarowska M (2011) Radiation and phylogeography in a spring snail Bythinella(Mollusca: Gastropoda: Rissooidea) in continental Greece. Ann Zool Fenn. 48: 67-90.
- Falniowski A, Szarowska M (2012) Sequence-based species delimitation in the Balkan BythinellaMoquin-Tandon, 1856 (Gastropoda: Rissooidea) with general mixed Yule coalescent model. Folia Malacologica 20: 111-120.
- Szarowska M, Falniowski A (2008) There is no philosopher’s stone: coup de grace for the morphology-based systematics in the rissooidean gastropods? 5th Congress of the European Malacological Societies, Ponta Delgada 28.
- Fretter V, Graham A (1962) British Prosobranch Molluscs. Their functional anatomy and ecology. Ray Society. University of California, California, USA.
- Haszprunar G (1988) On the origin and evolution of major gastropod groups, with special reference to the Streptoneura. J Moll Stud 54: 367-441.
- Szarowska M (2006) Molecular phylogeny, systematics and morphological character evolution in the Balkan Rissooidea (Caenogastropoda) Folia Malacol 14: 99-168.
- Templeton AR (1989) The meaning of species and speciation: a genetic perspective. In: Otte D, Endler JA (eds.). Speciation and its consequences. Sinauer Associates Inc., Sunderland (MA, USA. Pg No: 3-27.
- Mayr E (1942) Systematics and the Origin of Species. Columbia University Press, New York, USA.
- Avise JC (2000) Phylogeography, the history and formation of species. Harvard University Press, Cambridge,USA.
- Davis GM, Wilke T, Spolsky C, Qiu C-P, Qiu D-C, et al. (1998) Cytochrome Oxidase I-based Phylogenetic Relationships among the Pomatiopsidae, Hydrobiidae, Rissoidae and Truncatellidae Gastropoda: Caenogastropoda:Rissoacea). Malacologia 40: 251-266.
- Bichain JM, Gaubert P, Samadi S, Boisselier-Dubayle MC (2007) A gleam in the dark: phylogenetic species delimitation in the confusing spring-snail genus Bythinella Moquin-Tandon, 1856 (Gastropoda: Rissooidea: Amnicolidae).Mol Phyl Evol 45: 927-941.
- Wilke T, Davis GM (2000) Infraspecific mitochondrial sequence diversity in Hydrobia ulvae and Hydrobia ventrosa (Hydrobiidae: Rissooidea: Gastropoda): Do their different life histories affect biogeographic patterns and gene flow? Biol J Linn Soc 70: 89-105.
- Wilke T (2003) Salenthydrobia nov. (Rissooidea: Hydrobiidae): a potential relict of the Messinian salinity crisis. Zool J Linn Soc 137: 319-336.
- Falniowski A, Szarowska M, Grzmil P (2007) Daphniola Radoman, 1973 (Gastropoda: Hydrobiidae): shell biometry, mtDNA, and the Pliocene flooding. J Nat Hist 41: 2301-2311.
- Falniowski A, Szarowska M, Sirbu I (2009) Bythinella Moquin-Tandon, 1856 (Gastropoda: Rissooidea: Bythinellidae) in Romania: species richness in a glacial refugium. J Nat Hist 43: 2955-
- Szarowska M, Grzmil P, Falniowski A, Sirbu I (2007) Grossuana codreanui (Grossu, 1946) and the phylogenetic relationships of the East Balkan genus Grossuana (Radoman, 1973) (Gastropoda: Rissooidea). Hydrobiologia 579: 379-391.
- Falniowski A, Szarowska M, Glöer P, Peši? V (2012) Molecules vs morphology in the taxonomy of the Radomaniola/Grossuana group of Balkan Rissooidea (Mollusca: Caenogastropoda). J Conchol 41: 19-36.
- Szarowska M, Falniowski A (2013) Species distinctness of Sadleriana robici (Clessin, 1890) (Gastropoda: Rissooidea). Folia Malacol 21: 127-133.
- Szarowska M, Falniowski A (2014) Ventrosia maritima (Milaschewitsch, 1916) and ventrosa(Montagu, 1803) in Greece: molecular data as a source of information about species ranges within the Hydrobiinae (Caenogastropoda: Truncatelloidea). Folia Malacol 22: 61-67.
- Szarowska M, Hofman S, Osikowski A, Falniowski A (2014) Heleobia malzani (Westerlund, 1886) (Caenogastropoda: Truncatelloidea: Cochliopidae) from Crete and species-level diversity of HeleobiaStimpson, 1865 in Europe. J Nat Hist 48: 2487-
- Falniowski A, Szarowska M, Glöer P, Peši? V, Georgiev D, et al. (2012) Radiation in BythinellaMoquin-Tandon, 1856 (Mollusca: Gastropoda: Rissooidea) in the Balkans. Folia Malacol 20: 1-10.
- Falniowski A, Szarowska M (2012) Phylogenetic position of Boleana umbilicata (Kuš?er, 1932) (Caenogastropoda: Rissooidea). Folia Malacol 20: 265-270.
- Rysiewska A, Prevor?nik S, Osikowski A, Hofman S, Beran L, et al. (2017) Phylogenetic relationships in Kerkia and introgression between Hauffenia and Kerkia (Caenogastropoda: Hydrobiidae). J Zool Syst Evol Res 55: 106-
- Falniowski A, Szarowska M, Sirbu I (2009) Bythinella Moquin-Tandon, 1856 (Gastropoda: Rissooidea: Bythinellidae) in Romania: its morphology with description of four new species. Folia Malacol 17: 21-
- Davis GM (1992) Evolution of prosobranch snails transmitting Asian Schistosoma: coevolution with Schistosoma: a review. Prog Clin Parasitol 3: 145-204.
- Gittenberger E (1991) What about non-adaptive radiation? Biol J Linn Soc 43: 263-272.
- Cameron RAD (1992) Land snail faunas of the Napier and Oscar ranges, Western Australia: diversity, distribution and speciation. Biol J Linn Soc 45: 271-286.
- Cameron RAD, Cook LM, Hallows JD (1996) Land snails on Porto-Santo: adaptive and non adaptive radiation. Phil Trans Roy Soc Lond B 351: 309-327.
- Szarowska M (1996) The egg capsules of Bythinella austriaca (Frauenfeld, 1856) with observations on the veliger and embryonic shell. J Moll Stud 62: 546-549.
- Boeters HD (1979) Species concept of prosobranch freshwater molluscs in Western Europe, 1. Malacologia 18: 57-60.
- Georgiev D (2013) Catalogue of the stygobiotic and troglophilous freshwater snails (Gastropoda: Rissooidea: Hydrobiidae) of Bulgaria with descriptions of five new species. Ruthenica 23: 59-67.
- Falniowski A, Szarowska M, Fia?kowski W, Mazan K (1998) Unusual geographic pattern of interpopulation variation in a spring snail Bythinella (Gastropoda, Prosobranchia). J Nat Hist 32: 605-616.
- Falniowski A, Mazan K, Szarowska M (1999) Homozygote excess and gene flow in the spring snail Bythinella (Gastropoda: Prosobranchia). J Zool Syst Evol Res 37: 165-175.
- Barton NH (1989) Founder effect speciation. In: Otte D, Endler JA (eds.). Speciation and its consequences. Sinauer Associates, Sunderland (MA), USA. Pg No: 229-256.
- Schütt H (1980) Zur Kenntnisgriechischer Hydrobiiden. Arch Molluskenk 110: 115-
- Richling I, Malkowsky Y, Kuhn Y, Niederhöfer H-J, Boeters HD (2016) A vanishing hotspot-impact of molecular insights on the diversity of Central European Bythiospeum Bourguignat, 1882 (Mollusca: Gastropoda: Truncatelloidea). Org Div Evol 17: 67-85.
- Colgan DJ, Ponder WF (1994) The evolutionary consequences of restrictions on gene flow: Examples from Hydrobiid snails. Nautilus 2: 25-
- Ponder WF, Eggler P, Colgan DJ (1995) Genetic differentiation of aquatic snails (Gastropoda: Hydrobiidae) from artesian springs in arid Australia. Biol J Linn Soc 56: 553-596.
- Bohonak AJ (1999) Dispersal, gene flow, and population structure. Q Rev Biol 74: 21-45.
- Bilton DT, Freeland J R, Okamura B (2001) Dispersal in freshwater invertebrates. Ann Rev Ecol Sys 32: 159-181.
- Myers MJ, Sperling FAH, Resh VH (2001) Dispersal of two species of Trichoptera from desert springs: Conservation implications for isolated vs connected populations. J Insect Cons 5: 207-215.
- Finston TL, Johnson MS (2004) Geographic patterns of genetic diversity in subterranean amphipods of the Pilbara, Western Australia. Mar Freshw Res 55: 619-628.
- Hershler R, Liu H-P (2004) Taxonomic reappraisal of species assigned to the North American freshwater gastropod subgenus Natricola (Rissooidea: Hydrobiidae). Veliger 47: 66-81.
- Hershler R, Liu H-P (2004) A molecular phylogeny of aquatic gastropods provides a new perspective on biogeographic history of the Snake River region. Mol Phylogenet Evol 32: 927-937.
- Brändle M, Westermann I, Brandl R (2005) Gene flow between populations of two invertebrates in springs. Freshw Biol 50: 1-9.
- Hershler R, Mulvey M, Liu H-P (2005) Genetic variation in the Desert Springsnail (Tryoniaporrecta): implications for reproductive mode and dispersal. Mol Ecol 14: 1755-1765.
- Radoman P (1976) Speciation within the family Bythinellidae on the Balkans and Asia Minor. J Zool Syst Evol Res 14: 130-152.
- Falniowski A (1992) The genus Bythinella Moquin-Tandon, 1855, in Poland (Gastropoda, Prosobranchia, Hydrobiidae). In: Gittenberger E & Goud J (eds.), Proceedings of the 9th International Malacological Congress: 135- Unitas Malacologica, Leiden, Netherland.
- Szarowska M, Osikowski A, Hofman S, Falniowski A (2016) Do diversity patterns of the spring-inhabiting snail Bythinella (Gastropoda, Bythinellidae) on the Aegean Islands reflect geological history? Hydrobiologia 765: 225-
- Szarowska M, Osikowski A, Hofman S, Falniowski A (2016) Pseudamnicola Paulucci, 1878 (Caenogastropoda: Truncatelloidea) from the Aegean Islands: a long or short story? Org Divers Evol 16: 121-139.
- Rees WJ (1965) The aerial dispersal of Mollusca. J Moll Stud 36: 269-282.
- Wesselingh FP, Cadée GC, Renema W (1999) Flying high: on the airborne dispersal of aquatic organisms as illustrated by the distribution histories of the gastropod genera Tryonia and Planorbarius. Geol Mijnbouw 78: 165-174.
- Charalambidou I, Santamaria L (2002) Waterbirds as endozoochorous dispersers of aquatic organisms: a review of experimental evidence. Acta Oecol 23: 165-
- Figuerola J, Green AJ (2002) Dispersal of aquatic organisms by waterbirds: a review of past research and priorities for future studies. Freshwater Biol 47: 483-
- Lyell C (1832) Principles of Geology. John Murray, London UK.
- Darwin C (1859) The origin of species. General Press, Pennsylvania USA.
- Bondesen P, Kaiser EW (1949) Hydrobia (Potamopyrgus) jenkinsi Smith in Denmark illustrated by its ecology. Oikos 1: 252-281.
- Cadée GC (1988) Levendewadslakjes in bergeend faeces. Nederl Malacol Vereenig 243: 443-444.
- Cadée GC (1994) Eider, shellduck and other predators, the main producers of shellfragments in the Wadden Sea: palaeoecological implications. Palaeontology 37: 181-202.
- Purchon RD (1977) The Biology of the Mollusca: International Series of Monographs in Pure and Applied Biology: Division: Zoology (Vol 57). Elsevier Science Limited. Massachusetts, USA. Pg no: 560.
- Trueman ER (1983) Locomotion in Molluscs. In: Saleuddin ASM, KM Wilbur (eds.). The Mollusca (Vol 4). Academic Press Inc., Massachusetts, USA. Pg No: 155-198.
- Lamoreaux J (2004) Stygobites are more wide-ranging than troglobites. J Cave Karst Stud 66: 18-19.
- Culver DC, Pipan T, Schneider K (2009) Vicariance, dispersal and scale in the aquatic subterranean fauna of karst regions. Freshwater Biol 54: 918-929.
- Culver DC, Sket B (2011) Hotspots of Subterranean Biodiversity in Caves and Wells. J Cave Karst Stud 62: 11-17.
- Culver DC (2012) Mollusks. Encyclopedia of Caves (2nd). In: White WB, Culver DC (eds.). Academic Press, New York. Pg no: 512-517.
- Osikowski A, Hofman S, Georgiev D, Rysiewska A, Falniowski A (2017) Unique, Ancient Stygobiont Clade of Hydrobiidae (Truncatelloidea) in Bulgaria: the Origin of Cave Fauna. Folia Biol 65: 79-93.
- Rysiewska A, Georgiev D, Osikowski A, Hofman S, Falniowski A (2016) Pontobelgrandiella Radoman, 1973 (Caenogastropoda: Hydrobiidae): a recent invader of subterranean waters. Journal of Conchology 42: 1-11.
- Gittenberger E (1988) Sympatric speciation in snails: a largely neglected model. Evolution 42: 826-828.
- Tauber CA, Tauber MJ (1989) Sympatric speciation in insects: perception and perspective. In: Otte D, Endler JA (eds.). Speciation and its consequences. Sinauer Associates Inc., Sunderland (MA), USA. Pg no: 307-344.
Citation:Andrzej Falniowski (2018) Species Distinction and Speciation in Hydrobioid Gastropods (Mollusca: Caenogastropoda: Truncatelloidea). Archiv Zool Stud 1: 003.
Copyright: © 2018 Andrzej Falniowski, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.