Niphargus luxemburgensis Weber, Weigand & Brad, 2025

Niphargus luxemburgensis Weber, Weigand & Brad sp. nov.

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Figs 3–11 View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig

Diagnosis

Medium-sized Niphargus species, poorly setose. Right posteroventral angle of epimeral plates. Outer 6 spines of maxilla I on outer lobe with 1 tooth each; 1 spine with several smaller teeth. Mandibular palp with small number (1–2) of B setae. Gnathopods with 1 seta along outer margin of dactylopodites. Pereiopod VII, the longest leg, almost half of total body length. Pleopods retinaculum with 2 hooks. Uropod I, longer exopodite. Uropod II, longer endopodite. Uropod III sexually dimorphic, exopodite elongated in males. Telson with 3 apical spines on each lobe. The COI marker shows two pure diagnostic sites at positions 55 (C) and 358 (C). Six 28S rDNA alleles are diagnostic (with 13 heterozygous specimens) as well as 79 COI barcodes.

Etymology

The species name derives from the Grand Duchy of Luxembourg, where it was first discovered. In Weber et al. (2023), this species was treated as N. aquilex F, F’.

Material examined

Holotype

LUXEMBOURG • ♂; Girst, Gutland, basin of a spring in the center of the hamlet of Girsterklaus ; 49.7847° N, 6.4989° E; 19 Mar. 2018; Dieter Weber leg.; kept intact in 96% ethanol; 180319-10; MNHNL130574 .

GoogleMaps

Paratypes

LUXEMBOURG • 1 ♂; same collection data as for holotype; 30 Jan. 2018; dissected and appendages drawn; 180130-32; ISER microscope slide DW180130-32 GoogleMaps • 1 ♀; same collection data as for preceding; dissected and appendages drawn; 180130-45; ISER microscope slide DW180130-45 GoogleMaps • 1 ♂; same collection data as for holotype; 27 Mar. 2017; ISER DW170327-02 GoogleMaps • 1 ♀; same collection data as for holotype; 19 Mar. 2018; ISER DW180319-09 GoogleMaps • 1 ♀; same collection data as for holotype; 19 Mar. 2018; ISER DW180319-13 GoogleMaps • 1 ♀; same collection data as for holotype; 27 Mar. 2017; ISER DW 170327-06 ; MNHNL130575 GoogleMaps .

Molecular data

COI and 28S rDNA sequences of specimens belonging to Niphargus luxemburgensis sp. nov. were deposited in GenBank. COI and 28S rRNA accession numbers are present in Supp. file 6 and Supp. file 9, respectively.

Description (male paratype ISER DW 180130-32)

Measurements

Total body length 7.7 mm ( Fig. 3 View Fig ).

Head

Head ( Fig. 3 View Fig ) 8.60% of total body length. Eyes and rostrum absent.

Antennae

Antenna I ( Fig. 4A View Fig ): with the main flagellum formed of 18 articles representing 41% of total body length. Peduncle length ⅓ of total length of antenna I. The accessory flagellum ( Fig. 4B View Fig ) biarticulated; proximal article slightly longer than first article of main flagellum; distal article ¼ of total length of accessory flagellum, with 2 apical setae of different lengths and 1 aesthetasc. Aesthetascs ⅓ of respective flagellum articles ( Fig. 4C View Fig ).

Antenna II ( Fig. 4D View Fig ): flagellum formed of 8 articles and representing 40% of total length of antenna II. Most flagellum articles bear 1 short aesthetasc.

Mouthparts

Labium ( Fig. 5A View Fig ): large inner lobes with no setae. Outer lobes with 1 row of fine setae subapically on inner sides. Labrum (not shown) typical, subovoid shape.

Maxilla I ( Fig. 5B View Fig ): with 4 apical setae on distal article of palp. Six spines of outer lobe with 1 tooth each and 1 spine with several small teeth. Inner lobe with 1 apical seta.

Maxilla II ( Fig. 5C View Fig ): with inner lobe slightly shorter than outer lobe. 1 apical row of setae and 1 subapical seta on each lobe.

Left mandible ( Fig. 5D View Fig ): 5 teeth on incisor process. 5 teeth on lacinia mobilis. 5 serrated setae, alternated with 6 trifid setae, between lacinia mobilis and molar process.

Right mandible ( Fig. 5E View Fig ): 5 teeth on incisor process. 7 small teeth on lacinia mobilis. 3 serrated and 2 trifid setae between lacinia mobilis and molar process. Long seta on molar process.

Mandibular palps ( Fig. 5D–E View Fig ): highly similar and of same length. 3 articles account for 19% (article 1), 39% (article 2) and 42% (article 3) of total length of palp. Proximal article without setae, median article with 6–9 ventral setae. Distal article of palp with one group of 5 A setae, three groups with 1–2 B setae, 14 D setae and 4 E setae.

Maxilliped ( Fig. 6A View Fig ): with palp formed of 4 articles. Article 1 asetose. Article 2 with 18 setae aligned along inner margin. Article 3 with 5 apical setae, one group of 8 dorsal setae and one group of 5 setae on inner margin. Article 4 with 1 seta located on outer margin and 2 setae at nail insertion. Outer lobe with 7 apical setae and 8 flattened setae on inner margin. Inner lobe with 6 apical setae.

Gnathopods

Gnathopod I ( Fig. 6B View Fig ): coxal plate in shape of rectangular trapezoid, with depth larger than width (ratio depth:width 1.0:0.85). Basis length:width ratio 1.0: 0.43. Ischiopodite with one posteroventral group of 5 setae. Basis length: carpus length ratio 1.0: 0.54. Carpus with row of 10 setae of various lengths along ventral margin, group of 4 setae located anterodorsally and two groups of 3–5 setae on carpus surface close to ventral margin. Propodite nearly as long as wide, five groups of 2–4 setae on ventral margin, one group of 2 setae on dorsal margin, one group of 6 anterodorsal setae, one group of 6 anteroapical setae, 1 mesial seta on lateral surface, one group of 2 setae on lateral surface close to ventral margin and one group of 2 setae close to palmar corner. 1 strong palmar spine, 1 supporting spine and 2 denticulate spines present in palmar corner. Dactylopodite with claw 35% of total dactylopodite length and 1 seta along outer margin.

Gnathopod II ( Fig. 6C View Fig ): slightly larger than gnathopod I, with coxal plate in shape of rectangular trapezoid; coxal plate width almost similar in length with depth (ratio width: depth 1.0: 0.95). Ovoid gill. Basis length: width ratio is 1.0: 0.34. Ischiopodite with one posteroventral group of 5 setae. Basis length: carpus length ratio 1.0:0.56. Carpus with row of 12 setae of various lengths along ventral margin, group of 3 setae located anterodorsally and one group of 4 setae on carpus surface close to ventral margin. Propodite as long as wide, 6 groups of 2–5 setae on ventral margin, 1 seta on dorsal margin, one group of 4 anterodorsal setae and 5 anteroapical setae. 1 mesial seta on lateral surface, 2 setae close to palmar corner. 1 strong palmar spine, 1 supporting spine and 2 denticulate spines present in palmar corner. Dactylopodite with claw 37% of total dactylopodite length and 1 seta along outer margin.

Pereopods

Pereopod III ( Fig. 7A View Fig ): coxal plate in shape of rectangular trapezoid, ratio width-depth 1.0: 0.9. Propodite length: dactylus length ratio 1.0:0.4. Dactylus, with nail measuring half of total length of dactylus, 1 dorsal seta with plumose tip. Pereopod III equal in length to pereopod IV (pereopod III length: pereopod IV length ratio 1.0: 1.0).

Pereopod IV ( Fig. 7B View Fig ): relatively rectangular coxal plate, with concavity on posterior margin, width: depth ratio 1.0: 0.82. Propodite length: dactylus length ratio 1.0: 0.46. Robust dactylus, with nail measuring 0.44% of total length of dactylus; 1 dorsal seta with plumose tip and 1 seta at nail base.

Pereopod V ( Fig. 8A View Fig ): coxal plate of irregular shape, with deep concavity on ventral side and 1 anterior seta. Basis ovoid-rectangular shaped, length: width ratio 1.0: 0.66, 6 setae on posterior margin, 4 setae on anterior margin, 3 anteroapical setae of different lengths. Dactylus with one dorsal seta with plumose tip, 1 seta and 1 spine at nail base, which represents ⅓ of total dactylus length. Propodite length:dactylus length ratio 1.0: 0.45.

Pereopod VI ( Fig. 8B View Fig ): coxal plate smaller than that of pereopod V, but highly similar in shape and 1 posterior seta. Basis ovoid-rectangular shaped, length: width ratio 1.0: 0.67, 6 setae on posterior margin, 5 setae on anterior margin, 3 anteroapical setae of different lengths. Dactylus with 1 plumose seta on outer margin and 1 spine near nail base. Nail length slightly more than ⅓ of total dactylus length. Ratio propodite length: dactylus length 1.0:0.4.

Pereopod VII ( Fig. 8C View Fig ): longest leg ( 3.1 mm) of inspected paratype male. Coxal plate trapezoidal, with 1 seta on posterior margin. Basis ovoid-rectangular, ratio length: width 1.0: 0.6, 8 setae on posterior margin, 2 setae on anterior margin and 3 anteroapical setae of different lengths. Dactylus with 1 plumose seta on outer margin and 1 spine near nail base. Nail length slightly more than ⅓ of total dactylus length. Ratio propodite length: dactylus length 1.0: 0.36.

Pereopods V: VI: VII ratio 1.0: 1.34: 1.49.

Pleopods

Similar in shape and size (pleopod I depicted in Fig. 9A View Fig ), with unequal rami and 2 hooks on retinaculum.

Epimeral plates ( Fig. 9B View Fig )

Epimeral plate I with right postero-ventral angle, relatively straight ventral margin, convex posterior margin with 5 setae. Epimeral plate II with right postero-ventral angle, relatively straight ventral margin with 2 spines, convex posterior margin with 6 setae. Epimeral plate III with right posteroventral angle, relative straight ventral margin with 1 spine, convex posterior margin with 6 setae.

Uropods

Uropod I ( Fig. 10A View Fig ): with two dorso-lateral rows of 4 spines on peduncle. Exopodite slightly longer than endopodite, and ratio of exopodite length:endopodite length 1.0: 0.85. 1 strong spine at base of uropod I.

Uropod II ( Fig. 10B View Fig ): with 1 dorsal spine and 3 apical spines. Endopodite longer than exopodite, endopodite length:exopodite length ratio 1.0:0.81, both rami with low number of spines.

Uropod III ( Fig. 10C View Fig ): sexually differentiated, longer in males. Peduncle with 4 apical spiniform setae. Short endopodite about half the length of peduncle, with 2 apical setae. Proximal segment of exopodite longer than distal segment (ratio 1.0:0.77). Anterior margin of proximal segment of exopodite with 5 groups of 2–3 setae; posterior margin of exopodite with 3 groups of 1–2 setae; one group of 3 posteroapical setae. Distal segment of exopodite with 3 groups of 2 setae on anterior margin, 3 groups of 1–2 setae on posterior margin and 4 apical setae of different lengths.

Telson

Telson ( Fig. 10E View Fig ) nearly as wide as long (width: length ratio 0.95), with 1 subapical and 3 apical spines of different lengths on each lobe. Longest spine almost half of telson length. 2 thin setae of different lengths and plumose tip, 1 seta medially on 1 lobe.

Sexual dimorphism

The examined male and female are highly similar. Besides the usual sexual dimorphism (e.g., slightly smaller gnathopods, presence of oostegites, and slightly deeper coxal plates I– VI in females), in N. luxemburgensis sp. nov., female uropod III ( Fig. 10D View Fig ) is shorter compared to that of male. Female telson similar to that of the male, but smaller ( Fig. 10F View Fig ).

Intraspecific and interspecific variability

The intraspecific morphological variability of N. luxemburgensis sp. nov. appears to be very low. All morphological characters were nearly identical in all inspected specimens (data not shown).

Type locality, ecology and distribution

The type locality is the basin of a spring in the center of the hamlet of Girsterklaus (community of Girst, Gutland, Luxembourg) at 49.7847° N, 6.4989° E (Supp. file 3.2 & 3.3). The artificial basin is made of sandstone. The water contains algae; the bottom of the basin is covered with mud. Specimens of Niphargus luxemburgensis sp. nov. were found in the mud as well as among the algae. The water has a hardness of 15°GH (where one degree equals to 17.9 mg /l CaCO 3) and a slightly acidic pH of 6.7. There is no human access, neither to the actual spring, nor to the groundwater. We confirm the permanent presence of this species in the type locality as it was found on 10 July 2016, 4 September 2016, 30 January 2018, 17 February 2018 and 19 May 2018. In the same basin of the spring, N. schellenbergi sensu stricto was also found. We successfully collected 82 specimens of N. schellenbergi in 15 springs and 1 mine, at a distance of maximum 10 km around the type locality, in Luxembourg and in Germany, but could not find N. luxemburgensis there. The type locality was free of gammarids ( Amphipoda , Gammaridae ) during the periods of collection. Niphargus luxemburgensis seems to be a typical species of the interstitial environment (Supp. file 4.3). It is widely distributed from the UK and North to Central France, Belgium, Germany to the Czech Republic in the East ( Fig. 11 View Fig ). The frequent presence in Luxembourg and bordering Germany ( Rhineland-Palatinate, Saarland) must be most likely attributed to a more intense sampling in those regions.

Niphargus luxemburgensis sp. nov. is the only species described herein with two strongly divided subclades (F and F’). Although the genetic distance is relatively large, the connection in the haplotype network identifies both as belonging to the same species. The two clades cannot be distinguished morphologically. Nevertheless, they are geographically separated with only a small overlap: Clade F’, including the type locality, has its distribution in the North-Eastern half of France, Belgium, Luxembourg and the very West of Germany ( Fig. 11 View Fig ). Clade F is distributed in southern England, the very North of France, Belgium, Luxemburg, all over Germany without the North and the South, up to the Czech Republic ( Fig. 11 View Fig ). The geographic overlap of both clades includes Belgium, Luxembourg, and the very West of Germany. The higher number of sites for clade F might be a sampling artefact, as our dataset comprised many more sites in Germany than in France. It can be assumed that the two subclades of N. luxemburgensis are in the process of ecological speciation.

Niphargus luxemburgensis sp. nov. has a moderate geographical overlap with Niphargus vejdovskyi Wrześniowski, 1890 in the very East of its distribution range, with the latter having been described as N. puteanus var. vejdovskyi from wells in Prague ( Wrześniowski 1890), the village of Bechlín close to Roudnice and from the wells between Kralupy and Vodolka in Bohemia ( Czech Republic). Wrześniowski’s drawings are difficult to understand but show some similarities to the N. aquilex species group. This taxon was re-described as N. aquilex vejdovskyi and synonymised with N. aquilex var. bohemica Ortmann ( Schellenberg 1932) , based on material from Schneeberg in the Ore Mountains ( Saxony, Germany), from Brunersdorf ( Saxony, Germany). Schellenberg assumed that three females from Heligoland ( Schleswig-Holstein, Germany) also belong to this species. The inner lobe of the maxilla I of the specimens from Heligoland has 3 to 6 apical setae ( Schellenberg 1932), while N. luxemburgensis (as well as all other newly described species herein) has 1 apical seta only. Niphargus vejdovskyi is therefore not identical to N. luxemburgensis , but DNA sequences of the former are not yet available.