Mongolodiaptomus nakhonphanomensis, Watiroyram & Monongdern & Koompoot, 2025

Mongolodiaptomus nakhonphanomensis sp. nov.

Figs 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4 , 5 View Figure 5 , 6 View Figure 6 , 7 View Figure 7

Type locality.

A pond in the Nong Hua Ngua Village   GoogleMaps (Fig. 1 D View Figure 1 ), Na Khun Yai Sub-district, Na Wa District, Nakhon Phanom Province, north-eastern Thailand; coordinates: 17°30'01.47"N, 104°08'03.35"E, altitude: 153 m above sea level.

Material examined.

Holotype: one adult male dissected and mounted on one slide ( THNHM -IV-21117 ) GoogleMaps ; allotype: one adult female dissected and mounted on one slide ( THNHM -IV-21118 ) GoogleMaps ; paratypes: three adult males and three adult females dissected and mounted on one slide each ( NPU 2025–01-04 ) GoogleMaps . All specimens collected from the type locality on 30 July 2023 by Piyathida Monongdern.

Etymology.

The specific name nakhonphanomensis refers to Nakhon Phanom Province in north-eastern Thailand, where the new species was discovered. The Latin suffix “-ensis” denotes origin or place.

Description.

Adult male. Body length excluding caudal setae 2.1 mm ( holotype) (other males: mean = 2.0, n = 3) (Fig. 2 A View Figure 2 ). Rostrum (Fig. 1 B View Figure 1 ) with two spiniform processes. Pedigers 4 and 5 incompletely fused laterally (Fig. 1 A View Figure 1 ). Lateral wings (Fig. 2 A View Figure 2 ) asymmetrical: left wing prolonged downwards, the right wing expanded distally in lateral direction; both tipped with thin spine. Urosome (Fig. 2 E View Figure 2 ) orientated obliquely posteriad towards right side. Genital somite short, asymmetrical, with small seta on outer distal margin on right side. Urosomites 2–3 each with long hairs on mid-ventral surface; former somite longer than latter. Urosomite 4 with right posterolateral margin dilated; dorsoposterior margin expanded, overlapping part of following somite. Anal somite symmetrical; anal operculum small, with posterior margin slightly concave. Caudal rami (Fig. 2 A, E View Figure 2 ) symmetrical; each ramus expanded distally, with setules along both inner and outer margins; with six setae (setae II – VII): setae II – VI plumose, seta VII bare. Right ramus without chitinous processes or ventral prominences.

Antennules asymmetrical, with the right antennule transformed and geniculated, exhibiting sexual dimorphism. Right side antennula (Fig. 2 C, D View Figure 2 ) 22 - segmented. Setal formula: 1 + a (I), 3 + a (II), 1 + a (III), 1 + a (IV), 1 + a (V), 1 (VI), 1 + a (VII), 1 + s (VIII), 2 + a (VIX), 1 + s (X), 1 + s (XI), 1 + a + s (XII), 1 + a + s (XIII), 2 + a + s (XIV), 2 + a + s (XV), 2 + a + s (XVI), 2 + s (XVII), 1 + s (XVIII), 2 + s (XIX), 3 + s (XX), 2 (XXI), 4 + a (XXII). Segments 13 to 20 enlarged and elongated; segments 18 and 19 geniculated; segment 20 (antepenultimate) with comb-like process (four teeth). Left side antennula (Fig. 4 A View Figure 4 ) 25 - segmented, reaching beyond the caudal setae. Setal formula as follows: 1 + a (I), 3 + a (II), 1 + a (III), 1 (IV), 1 + a (V), 1 (VI), 1 + a (VII), 1 + s (VIII), 2 + a (IX), 1 (X), 1 (XI), 1 + a + s (XII), 1 (XIII), 1 + a (XIV), 1 (XV), 1 + a (XVI), 1 (XVII), 1 (XVIII), 1 + a (XIX), 1 (XX), 1 (XXI), 2 (XXII), 2 (XXIII), 2 (XXIV), 4 + a (XXV).

Antenna (Fig. 4 B View Figure 4 ): coxa with one seta on inner side; basis with two setae on inner distal margin. Exp seven-segmented, with 1, 3, 1, 1, 1, 1, 1 setae laterally, three setae apically. Enp two-segmented; Enp - 1 with two setae at 1 / 2 length, Enp - 2 with nine setae along inner margin and seven setae apically, accompanied by short row of spinules on distal outer margin.

Mandible (Fig. 4 C View Figure 4 ): coxa with five bi-cuspidate teeth and one blunt tooth on gnathobase; with small dorsal seta on distolateral corner. Basis with four setae along inner margin. Enp two-segmented; Enp - 1 with four setae on distal inner corner. Enp - 2 with nine setae apically, accompanied by row of spinules along outer margin. Exp 4 - segmented, with 1, 1, 1, and 3 setae, respectively.

Maxillule (Fig. 4 D View Figure 4 ): praecoxal arthrite with ten robust setae apically and four fine setae on dorsal side. Coxal endite with three fine setae; coxal epipodite with eight robust setae. Basis with two endites, each armed with four setae; basal exite with one small seta. Enp reduced, represented by eight setae apically. Exp with seven apical setae.

Maxilla (Fig. 4 E View Figure 4 ): proximal and distal praecoxal endites with four and three setae, respectively. Two coxal endites with three setae each. Allobasis with three setae on basal endite. Enp two-segmented, each with three setae.

Maxilliped (Fig. 4 F View Figure 4 ): coxa with four endites, bearing 1, 2, 3 and 4 setae, respectively. Basis with three setae distally plus row of strong spinules along inner margin. Enp six-segmented, with 2, 3, 2, 2, 2 and 4 setae, respectively.

P 1 – P 4 (Fig. 5 A – D View Figure 5 ). P 1 with two-segmented Enp and three-segmented Exp; P 2 – P 4 with three-segmented Enp and Exp; Exp longer than Enp. Coxa on P 1 – P 4 with pinnate seta at distal inner corner. P 4 basis with small seta at distal outer margin. Exp - 1 P 1 – P 4 with one robust spine on outer margin and pinnate seta on inner margin. Exp - 2 as Exp - 1, but P 1 without spine on outer margin. Exp - 3 with three pinnate setae on inner margin and three pinnate setae apically on P 2 – P 4, but two on P 1 inner margin. Enp - 1 P 1 – P 4 with one pinnate seta on inner margin. P 1 Enp - 2 with three setae on inner margin, two setae apically, one pinnate seta on outer margin. P 2 – P 4 Enp - 2 with two pinnate setae on inner margin. Enp - 3 P 2 – P 4 with three setae on inner margin, two setae apically and two pinnate setae on outer margin.

P 5 (Figs 3 View Figure 3 , 5E, F View Figure 5 ) asymmetrical, with right leg markedly enlarged. Intercoxal plate with rounded distal margin. Right side of P 5: coxa with spiniform seta on posterior lobe, not reaching mid-length of basis. Basis approximately twice as long as wide, with narrow hyaline lamella along proximal inner margin and hyaline prominence at mid-distal region; with small seta at 3 / 4 length of outer margin. Exp three-segmented: Exp - 1 shorter than wide, with unproduced distal outer corner and semicircular hyaline prominence distally. Exp - 2 elliptical, with distal portion broader than proximal one, about 2.5 times as long as wide; with strong blunt spine at 1 / 2 length of outer margin and blunt process distally. Spine curved backwards, slightly shorter than half segment length. Exp - 3 as sickle-shaped claw, about 1.5 times as long as Exp - 2; with inner margin serrated. Enp 1 - segmented, conical, gradually tapering distally, reaching the mid-length of Exp - 2; with spinulated tip. Left side of P 5: coxa with thin seta at distal inner margin, reaching beyond mid-half of basis. Basis with narrow hyaline lamella along distal inner margin; with short, thin posterolateral seta on outer margin. Exp three-segmented (Fig. 5 E, F View Figure 5 ): Exp - 1 longer than wide, gradually tapering in posterior end; with a hair field at distal half of inner margin. Exp - 2 oval, smaller than Exp - 1; with inner robust seta, accompanied by spinular field along inner margin. Exp - 3 reduced to a short, bare segment with rounded tip. Enp one-segmented, conical, gradually tapering distally; reaching end of Exp - 1, with spinulate tip.

Adult female. Body length excluding caudal setae 2.5 mm ( allotype) (other females: mean = 2.3, n = 3) (Fig. 6 A View Figure 6 ). Antennules symmetrical, with setal formula identical to that of the left antennule of male. Antenna and mouth appendages as in male. Cephalosome and pediger 1, as well as pedigers 4 and 5, completely fused. Pediger 5 (Figs 6 A View Figure 6 , 7 B View Figure 7 ) with asymmetrical posterolateral wings: right wing short, rounded, with strong large spine dorsally, tiny spine on posterior margin; left wing longer, subtriangular, with tiny spine dorsally, larger spine posteriorly. Urosome (Fig. 7 A View Figure 7 ) three-segmented; genital double-somite longer than two subsequent urosomites and caudal rami combined. Genital double-somite (Fig. 7 A View Figure 7 ) asymmetrical; left side broadly expanded laterally at the proximal part, with strong spine; right side with proximal part slightly expanded laterally. Both spines articulated, inserted on somite prominence. Urosomite 2 symmetrical, shorter than wide, partly covered by posterior end of genital double-somite. Anal somite and caudal rami as in male (Fig. 7 A View Figure 7 ).

P 5 (Figs 6 B, C View Figure 6 , 7 C, D View Figure 7 ) asymmetrical. Coxa with a stout spine on a prominence at the distolateral corner in dorsal view; coxal spine reaching proximal margin of Exp - 1. Basis with thin seta at 1 / 2 length of outer margin. Exp three-segmented, Enp two-segmented. Exp - 1 rectangular, about twice as long as wide. Exp - 2 triangular: right side shorter and stouter than left side (Fig. 6 C 1 View Figure 6 – 2 View Figure 2 ); inner margin with row of strong spinules; two longitudinal ridges ventrally; distal lateral seta strongly modified into short, stout spine (Fig. 6 D View Figure 6 ). Exp - 3 reduced to short, stout spine and long, thin seta. Enp cylindrical, extending beyond half-length of Exp - 1. Enp - 1 shorter than Enp - 2; Enp - 2 with circular row of spinules at narrowed apical end.

Variations.

In addition to body size differences, segment 20 of the right antennule in males have a comb-like process with two to five teeth (Fig. 2 D View Figure 2 ). The female P 5 Enp varies in length, extending from the middle to the distal end of Exp - 1. The size of the hyaline lamella on the right male P 5 basis also varies, appearing in long and narrow on the inner margin and rounded (Fig. 5 E View Figure 5 ) in the proximal-distal region.

Ecology and distribution.

At present, the new species has been recorded in seven samples, all collected from the Nawa District, Nakhon Phanom Province. It occurs in both temporary and permanent waterbodies. Physical and chemical parameters during sampling were: pH 6.2–7.01, temperature 27.2–31.2 ° C, conductivity 14.73–108.6 µS / cm, total dissolved solids ( TDS) 7.34–52.5 mg / l. The co-occurring copepod species include Dentodiaptomus javanus (Grochmalicki, 1915) , Eodiaptomus draconisignivomi Brehm, 1952 , E. phuphanensis Sanoamuang, 2001 , Heliodiaptomus elegans Kiefer, 1935 , Mongolodiaptomus dumonti Sanoamuang, 2001 , M. malaindosinensis ( Lai & Fernando, 1978) and Neodiaptomus yangtsekiangensis Mashiko, 1951 .