Holotype. Male, 11.5 mm (ESFM-MALI/20–15), Akçakoca District, Düzce Province, Türkiye (41°3'7.01"N, 31°10'38.70"E), 16.xiii.2020; collected by M. Elverici.

Paratypes. 3 males and 5 females, (ESFM-MALI/20–16), same data as holotype.

A medium-large species. Body smooth, pigmentation weak; eyes well-developed, ovoid; extremities not prolonged; second antenna with setose peduncular and flagellar segments; antennal gland cone long; medial palmar spine present; posterior margin of pereopod 3 densely setose; anterior margins of pereopods 5 to 7 armed with spines and a few short setae; epimeral plates not pointed; inner ramus of uropod 3 longer than 0.75 of the outer one; telson weakly armed.

Head : Rostrum absent, inferior antennal sinus deep, rounded. Eyes kidney-shaped; shorter than the diameter of the first peduncular segment of antenna 1 (Figs 1, 5G).

Antennae : Antenna 1 is as long as half of the body length; the length ratio of the peduncular segments is 1:0.67:0.4; peduncle segments bear a few groups of minute setae; the length of the setae is much shorter than the segment where they are implanted; the main flagellum with 32 segments; each segment bears a few short setae in distal side; aesthetasc absent; accessory flagellum 6 segmented (Fig. 3A). Antenna 2 is shorter than antenna 1 (ratio 1:0.67); the antennal gland cone is straight, reaches to the distal end of the third peduncular segment; setation is rich both on peduncular and flagellar segments; peduncular segments 4 and 5 bear many groups of setae; the setae on the ventral part of the peduncle segments are longer than the dorsal ones and can be up to 1.5 times longer than the diameter of the segment; flagellum consists of 15 segments; flagellar segments are setose and swollen; each segment bears many long setae on both dorsal and ventral sides; calceoli absent (Fig. 3B).

Mouthparts : Left mandible (Fig. 2A) with 5-toothed incisor, lacinia mobilis with 3 dentitions, molar triturative. The first article of palp without setae, the second one bears 12 setae; the setae become shorter from distal to proximal. The third segment has 28 D-setae, 4–5 E-setae, one group of A-setae and one group of B-setae. C-setae absent.

Figure 2. 

Gammarus kunti sp. nov., (male holotype). A. Left mandible; B. Right mandible; C. Maxilla 2; D. Lower lip 1; E. Maxilliped; F. Left maxilla 1; G. Right maxilla 1; H. Upper lip.

Right mandible (Fig. 2B) has a 4-toothed incisor and bifurcate lacinia mobilis.

Right maxilla I (Fig. 2G) is asymmetric to the left, it has 14 plumose setae along the inner margin of the inner lobe. The outer lobe bears 11 distal stout serrate spines and some tiny setules on the inner margin. Palp of the outer lobe with no setae in the first segment and six stout spines and two simple setae on the distal part of the second segment, in addition to two marginal setae along the outer margin. The second article of left palp elongated and bears 8 spines and 3 simple setae on its distal part and no setae along the outer margin (Fig. 2F).

Lower lip (Fig. 2D) has no inner lobe and bears numerous small simple setae along the distal margins of both lobes.

Upper lip (Fig. 2H) with numerous minute setules in the distal part.

Maxilla II (Fig. 2C) has 20–25 simple setae in the distal part of the outer lobe and a few tiny hairs along the outer margin. The inner lobe also has 8–10 simple setae in the distal part in addition to 15 plumose setae located in a diagonal row along the inner margin. There are also a few tiny hairs in the proximal part of the inner margin of the lobe.

Maxilliped (Fig. 2E) inner plate has 3 tooth-like spines and a spine in the distal part and the distal corner, respectively. Additionally, there are 7 plumose setae along the inner margin of the lobe. Outer plate armed with 5–6 serrate stout setae in the distal part and 12 spines along its inner margin.

Coxal plates : Coxal plate 1 is rectangular, the distal part slightly widened, the ventral margin slightly convex and bears 4 antero-distal setae and one postero-distal seta in addition to some tiny setules along the ventral margin (Fig. 3C). Coxal plate 2 is in the shape of an elongated rectangle, distal part narrower than the proximal, the ventral margin is highly convex, antero-distal part with 5 setae and postero-distal part with one seta (Fig. 3D). Coxal plate 3 is similar to coxal plate 2 in shape, with 3 and 1 setae in the antero- and postero-distal ends, respectively (Fig. 4A). The ventral edge of the fourth coxal plate is slightly convex and bears 3 and 6 setae along the anteroventral and posterior margins, respectively (Fig. 4B). Coxal plate 5 (Fig. 5A) and Coxal plate 6 exhibit a bilobate structure (Fig. 5B), each having one seta in the anterior lobes and four and one setae in the posterior lobes, respectively. Coxal plate 7 is characterised by the presence of five setae on the postero-ventral margin (Fig. 5C).

Figure 3. 

Gammarus kunti sp. nov., (male holotype). A. Antenna 1; B. Antenna 2; C. Gnathopod 1; C’. Palm of gnathopod 1; D. Gnathopod 2; D’. Palm of gnathopod 2.

Figure 4. 

Gammarus kunti sp. nov., (male holotype). A. Pereopod 3; B. Pereopod 4; C. Uropod 1, D. Uropod 2; E. Uropod 3; F. Telson.

Figure 5. 

Gammarus kunti sp. nov., (male holotype). A. Pereopod 5; B. Pereopod 6; C. Pereopod 7; D. Pleopod 1; E. Pleopod 2; F. Pleopod 3; G. Head; H. Urosomites.

Gnathopods : Basal segment of gnathopod 1 bears many long setae along both margins, the length of the setae can be as long as twice the diameter of the segment. Ischium bears a group of setae in the postero-ventral corner. Carpus is triangular and bears four groups of setae along the anterior margin in addition to many setae groups on both ventral and posterior sides. Propodus pyriform, the length/width ratio is 1: 0.57, anterior margin with two groups of setae, medial palmar spine is present, postero-distal corner armed with two strong spines in addition to some small spines, posterior margin bears 4–5 groups of setae. Dactylus reaches the postero-distal corner and bears a simple seta along the outer margin in addition to a small setule around the distal part of the inner margin (Fig. 3C, C’).

Basis and ischium of gnathopod 2 have a similar setation to that of gnathopod 1. Merus and carpus are more setose than those of gnathopod 1. Carpus triangular, densely setose along the posterior margin in addition to two groups of setae along the anterior margin. Propodus is densely setose and has a sub-rectangular shape, the length/width ratio is 1: 0.53, anterior margin bears 6 groups of setae, posterior margin with many groups of setae, medial palmar spine is present, the postero-distal corner is armed with two strong spines in addition to some small spines. Dactylus reaches the postero-distal corner and bears a simple seta along the outer margin in addition to a small setule around the distal part of the inner margin (Fig. 3D, D’).

Pereopods : Anterior and posterior margins of the basal segment of pereopod 3 bear long setae, the setae along the posterior margin are much longer than those in the anterior margin, posterior margins of the merus, carpus and propodus bear long setae, the setae can be more than three times the diameter of the segment where they are implanted. Dactylus slim, a minute plumose seta occurs on the outer margin; the inner margin with two small setules (Fig. 4A).

The basal segment of pereopod 4 has a similar setation to that of pereopod 3. Ischium, merus, carpus and propodus have groups of setae along their posterior margins, but they are much shorter and less than those in pereopod 3, the length of the setae can be as long as (or slightly longer) than the diameter of the segment where they are implanted. Dactylus slim, a minute plumose seta occurs on the outer margin; the inner margin with two small setules (Fig. 4B).

Posterior margins of the basal segments of pereopods 5 to 7 are more or less convex and bear many short setae, anterior margins with 5–7 small spines and no setae present on the inner surfaces of the basal segments; no spine exists in the postero-ventral corner of the basal segment of pereopod 7. Pereopods 6 and 7 bear no setae along the anterior margins of ischium, merus and carpus, while pereopod 5 has a few setae longer than the accompanying spines along with the mentioned segments. Propodus of pereopods 5 to 7 with 2–3 groups of long setae groups along their outer margins in addition to 5–6 groups of small spines along their inner margins. Dactylus slim, a minute plumose seta occurs on the outer margin; the inner margin with two small setules (Fig. 5A–C).

Epimeral plates : They are neither curved nor sharply pointed. Epimeral plate 1 bears 2 long setae in addition to 4–5 setules along the anterior margin, the postero-ventral corner is angular (Fig. 5D). Epimeral plate 2 bears 5–6 setae in the antero-ventral corner, the ventral margin is armed with 1 spine and two short setae, the posterior margin with 4–5 setules, the postero-ventral corner is angular (Fig. 5E). Epimeral plate 3 is slightly pointed; the antero-ventral corner bears 3–4 setae; the ventral margin is armed with 3 spines; the posterior margin bears 6–7 setules (Fig. 5F).

Urosomites : Not elevated. Each segment bears a median and two dorsolateral groups of armaments; each of them consists of 1–2 spines and 3–4 accompanying setae (Fig. 5H).

Uropods : Uropod 1 has a spine in the disto-ventral corner of the base; the peduncle is longer than the rami; the length ratio is about 1:0.7. Peduncle with a spine in the outer margin of the proximal part in addition to 3 spines along the inner margin and 3 spines in the distal part. The inner ramus is slightly longer than the outer ramus and bears 3–4 spines along their inferior margin in addition to 4–5 distal spines. The outer ramus with 2 spines along the inferior margin in addition to 4–5 distal spines (Fig. 4C).

Uropod 2 is smaller than the first one; the length ratio is about 1:0.6; the peduncle segment is slightly longer than the rami and bears 2+2 spines along the inner margin and the distal part, respectively. The outer margin is bare. The length and armaments of both rami are similar to each other, bearing 2–3 spines along their inner and outer margins in addition to 4–5 longer spines on their distal tips (Fig. 4D).

Uropod 3 is setose and bears simple and plumose setae. The peduncle segment is much shorter than the outer ramus and the length ratio is about 1:0.41. The outer ramus is two articulated and densely setose along both margins; the outer margin bears 2 groups of spines accompanied by groups of long simple setae; the inner margin with plumose setae; the second article is well developed and longer than the surrounding distal spines. The inner ramus is about 0.77× the length of the outer ramus. It bears two spines along the outer margin in addition to groups of simple and plumose setae; the inner margin bears both simple and plumose setae (Fig. 4E).

Telson : Telson lobes cleft, each lobe bears 2 spines and 2–3 simple setae in their distal parts. The setae are longer than the spines. There are 2–3 groups of short setae on the dorsal surface of the lobes in addition to two plumose setules. The length/width ratio of each lobe is about 1:0.5 (Fig. 4F).

The species epithet is derived from the name of scientist Dr. Kadir Boğaç Kunt, who has valuable contributions to the Arachnida species of Türkiye and sent the materials for this study.

Smaller than males. Except for the sexual dimorphism indicated for the genus Gammarus, females do not show obvious differences from males. At first glance, the morphological differences between the female allotype and the male holotype can be listed as follows: less setose antenna 2, not swollen flagellar segments of antenna 2, less setose gnathopod 2 and more setose pereopods 4–7 (Figs 6, 7).

Figure 6. 

Gammarus kunti sp. nov., (female allotype). A. Antenna 1; B. Antenna 2; C. Gnathopod 1; D. Gnathopod 2; E. Pereopod 3; F. Pereopod 4; G. Uropod 3; H. Telson.

Figure 7. 

Gammarus kunti sp. nov., (female allotype). A. Pereopod 5; B. Pereopod 6; C. Pereopod 7.

Variability : Some of the paratypes are immature. The eyes are kidney-shaped or slightly oval. The number of flagella segments in antenna 1 varies between 26 and 29. Similarly, there are 10–11 flagellar segments in antenna 2.

Molecular data analyses

We generated the partial sequences of the COI (573 bp) and 28S (914 bp) genes of the newly-described species, Gammarus kunti. After all sequences were aligned, the total length is 1489 bp including gaps. While no stop codon, insertion, deletion and a gap was detected in the protein-coding mtDNA COI gene, there were insertions and deletions in the nuclear 28S gene. Additionally, newly-generated sequences are deposited in GenBank accession numbers, for COI; OP642558 and 28S; OP650556. Thus, the first genetic record of the newly-described species was created. We performed the genetic comparison of the new species with the reference sequences of the topotype samples of the nominal taxa in GenBank. In the absence of sequences of topotype samples, correct sequences considered representative of the species were preferred (Table 1).

For the COI gene, the pairwise genetic distance amongst the species ranged from a minimum of 5.24% (G. stankokaramani - G. salemaai) to a maximum of 28.62% (G. kesslerianus - G. plaitisi). The pairwise genetic distances between the new species Gammarus kunti sp. nov. and the other species ranged from a minimum of 16.23% (G. tumaf) to a maximum of 28.27% (G. roeselii). For the 28S gene, the pairwise genetic distance amongst the species ranged from a minimum of 0.11% (G. halilicae - G. pljakici) to a maximum of 7.84% (G. rambouseki - G. stojicevici).

The pairwise genetic distances between the new species Gammarus kunti sp. nov. and the other species ranged from a minimum of 0.88% (G. tumaf) to a maximum of 6.81% (G. balcanicus). The genetic distance of the new species to the nearest species is approximately three times greater for the COI gene and eight times greater for the 28S gene than the minimum genetic distance between valid Gammarus species. This indicates that the new species is well differentiated genetically. All pairwise genetic distance values amongst Gammarus species are given in Suppl. material 1.

Phylogenies generated by the NJ and ML methods, based on the concatenated data, yielded fully compatible trees. Except for a few branches (ML:16–67%; NJ:25–69%), the other branches (ML: 82–100%; NJ: 83–100%) in the phylogenies were generally resolved and supported with high bootstrap values. G. tumaf Özbek et al., 2023 and G. baysali Özbek et al., 2013 are the sister taxa of G. kunti sp. nov. The phylogenetic position of the new species, Gammarus kunti sp. nov., indicates an independent lineage supported by high bootstrapping values (for NJ: 95%, for ML: 91%; Fig. 8).

Figure 8. 

Maximum Likelihood (ML) phylogenetic tree generated, based on the concatenated dataset (28S+COI). ML and NJ methods yielded the same topologies and, therefore, only the ML tree is shown. The bootstrap values of NJ and ML are shown on nodes (NJ/ML).

The species delimitation analysis we implemented according to the ASAP method, based on COI data, identified 26 MOTUs (molecular operational taxonomic units) for 27 Gammarus species. The best ASAP score had 1.5 (p = 0.01) at a threshold distance of 0.079053. The analysis identified species G. stankokaramani and G. salemaai as a single MOTU. The new species formed a single MOTU independent of other species.