With over 300 described species and subspecies, the genus Niphargus Schiödte, 1847 (Amphipoda: Niphargidae) is the largest genus of freshwater amphipods (Väinölä et al. 2008). Most of the species inhabit subterranean waters and constitute a substantial part of Europe’s groundwater biodiversity (Sket 1999a, b). The genus is distributed across most of Europe, mainly – but not exclusively – south of the Pleistocene ice sheet boundary (Ruffo 1953; Karaman & Ruffo 1986; Proudlove et al. 2003). Few species are known from the Arabian Peninsula, Turkey and Iran (Karaman 1986, 1998; Bat et al. 2001). Over most of the Pyrenean Peninsula only its presumed relative Haploginglymus Mateus & Mateus, 1958 can be found.
Most of the species are narrow endemics, even those occurring in surface waters. Recent molecular study suggests that nominal species with large ranges consist of several cryptic species that are not necessarily closely related. The upper estimation of a species range size is approximately 200 km.
The origin of the genus Niphargus remains an enigma. The highest species diversity coupled with the highest degree of ecological and morphological differentiation in the northern parts of Balkan Peninsula and in Danubian-Carpathian region evoked the hypothesis that the genus differentiated during upper Tertiary in the basins of the Paratethys and from that region subsequently colonized European freshwaters. However, this hypothesis has recently been questioned by three fossilized specimens (see N. groehni) preserved in Eocene Baltic amber suggesting that the group may be as old as 30-50 Mys.
Different species inhabit virtually all types of subterranean waters like the interstitial and different types of cave waters including subterranean flows and lakes, fissure systems (including epikarst), wells and springs, as well as brackish, mineral and thermal waters. In addition, about a dozen species live in surface waters such as forest ditches, Sphagnum moss or small streams.
Niphargus shows an extremely diverse morphology (for review see online supplement) caused mainly by highly variable body parts combined in many different combinations. The high number of character combinations differing in only one or few details often make taxonomic decisions difficult if not impossible without additional information, for example through molecular phylogeny.
In addition, some appendages of several species appear in late ontogeny in a remarkably modified form, such that juvenile specimens of these species can look more similar to adults of only distantly related species than to adults of their own species (review in Fišer et al. 2008). An important viewpoint introduced by recent molecular studies (Mathieu et al. 1997; Lefébure et al. 2006, 2007; Trontelj et al. in press) suggest that either there exists a high level of cryptic species diversity or that morphology is – at least in some “species” – heavily understudied. Hopefully, this online morpho-database will clarify and improve future taxonomy of the group.
Beside Niphargus, seven other genera with only one to three species each constitute the family Niphargidae. The position of the family among the amphipods is not clear. Some recent studies consistently offer arguments that niphargids are a monophyletic group in a sister relationship with crangonyctids (Englisch & Koenemann 2001; Englisch et al. 2003; Fišer et al. in press). By contrast, the justification the generic subdivision of the Niphargidae has recently been questioned. Both, morphological and molecular data imply that acceptance of Niphargopsis turns Niphargus paraphyletic. Finally, although the deep splits within Niphargus remain unidentified, a recent molecular study identified several well supported groups. Most of these groups are morphologically rather heterogeneous. In spite of extensive study of their morphology they cannot be diagnosed. The species structure of these clades largely disagrees with subgeneric classifications proposed by earlyer researchers, invalidating all proposals of taxonomic subdivision.
A revision of the group is urgently needed. Niphargus has several properties that could make it an important model-group in the fields of taxonomy, phylogeny, evolution, development, functional morphology, biogeography, ecology, and applied environmental studies.
A BRIEF HISTORY OF TAXONOMY
The description of “Gammarus puteanus Koch” published by Panzer in “Faunae Insectorum Germanicae Initia” in 1836 is the first unambiguous record of a Niphargus . A year later, Koch (the author of the species!) published the identical description and drawings in “Deutschlands Crustaceen, Myriapoden und Arachniden”. The genus Niphargus was established 13 years later when Schiödte re-examined his own description of Gammarus stygius from the cave Postojnska jama in Slovenia.
Till 1900, altogether 13 taxa had been described. The most fruitful period of taxonomy was 1930-1960 with approximately 170 described new taxa. The number of newly described taxa decreased significantly in the past two to three decades.
Most remarkable is the contribution of the Karaman family. Stanko Karaman and his son Gordan described 118 taxa (Stanko 63, Gordan 50, five co-authored descriptions); apart from those Gordan in co-authorship described another 10 taxa. Other important workers are Birštejn (17 taxa), Dobreanu & Manolache (12), Ruffo (10 alone and 6 in co-authorship), Schellenberg (33) and Sket (20 alone and 11 in co-authorship). The list of niphargid species today counts over 300 names.
The family Niphargidae was designated by S. Karaman in 1962 and later accepted by Bousfield (1978, 1983). The family consists of the genus Niphargus and some smaller genera (but see above for problems with non-monophyly): Carinurella Sket 1964 (1 species), Foroniphargus Karaman G. 1985 (1 species), Haploginglymus Mateus in Mateus 1958 (4 species), Martynovia Deržavin 1945 (1 species), Niphargobates Sket 1981 (2 species), Niphargopsis Pratz 1866 (1 species), Niphargellus Schellenberg 1933 (2-3(?) species) and Pontoniphargus Dancău 1970 (2 species).
In order to accelerate progress in the field of Niphargus taxonomy, five international meetings were organized. The first, known as “Ier Colloque International sur le genre Niphargus” was held in 1969 in Verona, and was followed by the meetings in Lyon (1973), Schiltz (1975), Blacksburg (1978) and Lødz (1980). However, apart form few publications little progress has been made in this field. Judging from the number of publications, the interest for the group seriously declined by the end of last century. The introduction of molecular techniques provided some remarkable taxonomic and phylogenetic insights that revived the interest for the group all over the Europe. Apart from the Ljubljana laboratory, several researchers showed an interest for the group including (in alphabetical order) T. Brad [Romania], B. Çamour-Elipek [Turkey], C. O. Coleman, A. Fuchs, R. Gerecke [all Germany], S. Gottstein Matočec [Croatia], V. Ianilli [Italy], S. Matthijs [Belgium], G. Karaman [Montenegro], L. Kenderov [Bulgaria], S. Koenemann [Germany], T. Lefébure [France], O. Moldovan [Romania], J. Notenboom [Netherlands], G. Proudlove [GB], F. Stoch [Italy] and P. Wood [GB].